Include cstdint and Point.hpp where the new code uses uint8_t and Vec2f

The clang-tidy job checks include-what-you-use on changed lines, and the three
files it named relied on a transitive include for a symbol the new code
introduced.

resources/images/texture_displacement_map_model_uv.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16"><path d="M2.5,2.5h11v11h-11z" style="fill:none;stroke:#949494;stroke-linecap:round;stroke-linejoin:round"/><path d="M8,2.5v11M2.5,8h11" style="fill:none;stroke:#949494;stroke-dasharray:1.5,1.5"/><path d="M4.5,11.5l3.5-6l3.5,6z" style="fill:#009688"/></svg>

src/libslic3r/Model.cpp

@@ -353,6 +353,24 @@ Model Model::read_from_file(const std::string&
         ObjInfo                 obj_info;
         ObjParser::MtlData      mtl_data;
         result = load_obj(input_file.c_str(), &model, obj_info, message, nullptr, &mtl_data);
+        // Keep the model's own UV channel on the volume, whatever the colour import then does with
+        // the mesh: it is what TextureProjectionMethod::ModelUV maps a texture-displacement layer
+        // through, so a model that arrives with a UV layout is textured on that layout instead of on
+        // a fresh unwrap. load_obj() fills obj_info.uvs per face of the mesh it built, in the same
+        // order (and only when every face named a known material, hence the size check). V is flipped
+        // on the way in, to the convention DecodedHeightTexture samples in - the same flip
+        // obj_to_textured_mesh() does for the colour importer.
+        if (result && !obj_info.uvs.empty() && !model.objects.empty() && !model.objects.back()->volumes.empty()) {
+            ModelVolume                &volume = *model.objects.back()->volumes[0];
+            const indexed_triangle_set &its    = volume.mesh().its;
+            if (obj_info.uvs.size() == its.indices.size()) {
+                volume.texture_uv.resize(its.indices.size() * 3);
+                for (size_t fi = 0; fi < obj_info.uvs.size(); ++fi)
+                    for (int k = 0; k < 3; ++k)
+                        volume.texture_uv[fi * 3 + size_t(k)] =
+                            Vec2f(obj_info.uvs[fi][size_t(k)].x(), 1.f - obj_info.uvs[fi][size_t(k)].y());
+            }
+        }
         if (result && obj_info.has_uv_png && !obj_info.uvs.empty() && !model.objects.empty()) {
             // Textured OBJ: hand the mesh + materials to the texture-to-color importer
             // instead of the flat per-face colour dialog.
@@ -2133,6 +2151,10 @@ void ModelVolume::reset_extra_facets()
     // than left referring to a mesh that no longer matches it.
     for (int i = 0; i < int(TEXTURE_DISPLACEMENT_MAX_LAYERS); ++i)
         this->texture_displacement_facet(i).reset();
+    // Same reasoning for the model's own UV channel: it is indexed by triangle, so against a mesh
+    // this no longer matches it would map the texture by another mesh's triangle numbering. A caller
+    // that can carry it across - see transfer_uv_channel() - puts it back after this.
+    this->reset_texture_uv();
 }
 
 std::optional<TriangleSelector::SavedPainting> ModelVolume::save_painting() const

src/libslic3r/Model.hpp

@@ -974,6 +974,26 @@ public:
     // they are not a property of any single layer.
     TextureDisplacementOptions texture_displacement_options;
 
+    // The model's own texture coordinates, as the file it was imported from carried them: three per
+    // triangle of mesh().its, in its triangle order (corner k of triangle i at 3i+k), V already
+    // flipped to the sampling convention (V = 0 is the image's top row). Empty when the source had
+    // none, which is every STL and every 3mf - only a textured OBJ brings one in today.
+    //
+    // Per corner rather than per vertex because that is what a UV layout is: the two sides of a seam
+    // are the same vertex with two different coordinates, and collapsing them would smear the texture
+    // across every island boundary. TextureProjectionMethod::ModelUV maps through it, which is what
+    // lets a model that already carries a UV channel be textured on the artist's own layout instead
+    // of on a fresh unwrap.
+    //
+    // Indexed by triangle, so anything that *replaces* the mesh has to bring it across (or drop it):
+    // see transfer_uv_channel(), and reset_texture_uv() for the cases that cannot.
+    std::vector<Vec2f> texture_uv;
+
+    bool has_texture_uv() const { return !texture_uv.empty() && texture_uv.size() == mesh().its.indices.size() * 3; }
+    // Forgets the channel. For a mesh change that nothing can carry it across - a split, a boolean -
+    // where leaving it would map the texture by another mesh's triangle numbering.
+    void reset_texture_uv() { texture_uv.clear(); }
+
     // Save painting data before reset_extra_facets() discards it.
     // Used for replacing mesh without losing painting data.
     // Only for model parts (not modifiers/connectors).
@@ -1236,6 +1256,7 @@ private:
         texture_displacement_facets_6(other.texture_displacement_facets_6), texture_displacement_facets_7(other.texture_displacement_facets_7),
         texture_displacement_layers(other.texture_displacement_layers),
         texture_displacement_options(other.texture_displacement_options),
+        texture_uv(other.texture_uv),
         cut_info(other.cut_info), text_configuration(other.text_configuration), emboss_shape(other.emboss_shape)
     {
 		assert(this->id().valid());
@@ -1334,7 +1355,7 @@ private:
             cereal::load_by_value(ar, f);
             mesh_changed |= tf != f.timestamp();
         }
-        ar(texture_displacement_layers, texture_displacement_options);
+        ar(texture_displacement_layers, texture_displacement_options, texture_uv);
         cereal::load_by_value(ar, config);
         cereal::load(ar, text_configuration);
         cereal::load(ar, emboss_shape);
@@ -1358,7 +1379,7 @@ private:
         cereal::save_by_value(ar, fuzzy_skin_facets);
         for (int i = 0; i < int(TEXTURE_DISPLACEMENT_MAX_LAYERS); ++i)
             cereal::save_by_value(ar, texture_displacement_facet(i));
-        ar(texture_displacement_layers, texture_displacement_options);
+        ar(texture_displacement_layers, texture_displacement_options, texture_uv);
         cereal::save_by_value(ar, config);
         cereal::save(ar, text_configuration);
         cereal::save(ar, emboss_shape);

src/libslic3r/TextureDisplacement.cpp

@@ -157,33 +157,12 @@ struct SmoothedTextureCache
     {
         std::weak_ptr<const std::vector<unsigned char>> source;
         float                                           smoothing = 0.f;
-        // Part of the key, not of the result: smoothing is applied *after* the panel's adjustments, so a
-        // blur computed over one set of adjustments is not the blur another set would give.
-        TextureAdjustments                              adjust;
         DecodedHeightTexture                            texture;
     };
     std::mutex                                   mutex;
     std::unordered_map<const void *, Entry>      entries;
 };
 SmoothedTextureCache g_smoothed_texture_cache;
-
-// The adjusted copy, cached between the raw decode and the smoothed one. Needed for the same reason the
-// smoothed cache is: while a slider in the image-adjustment panel moves, the thumbnail, the shaded
-// preview's height and colour textures, the UV editor backdrop and the displacement preview job all ask
-// for the same (image, adjustments) pair within one frame, and each of them running a full-size resample
-// of its own is what would make the panel unusable on a large texture.
-struct AdjustedTextureCache
-{
-    struct Entry
-    {
-        std::weak_ptr<const std::vector<unsigned char>> source;
-        TextureAdjustments                              adjust;
-        DecodedHeightTexture                            texture;
-    };
-    std::mutex                              mutex;
-    std::unordered_map<const void *, Entry> entries;
-};
-AdjustedTextureCache g_adjusted_texture_cache;
 } // namespace
 
 namespace {
@@ -359,34 +338,6 @@ DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer
         entries[key] = { std::weak_ptr<const std::vector<unsigned char>>(layer.image_data), result };
     }
 
-    // The image-adjustment panel's live edits, on top of the decode and before the smoothing. Before,
-    // because `preview_adjust` is an edit to the image while `smoothing` is a live low-pass over whatever
-    // the image is - the same order the panel presents them in, and the same order a commit bakes in.
-    //
-    // Nothing applies here once the panel has closed: it resets preview_adjust to identity, and identity
-    // is a no-op that costs one comparison.
-    if (!layer.preview_adjust.identity()) {
-        bool have_adjusted = false;
-        {
-            std::lock_guard<std::mutex> lock(g_adjusted_texture_cache.mutex);
-            auto it = g_adjusted_texture_cache.entries.find(key);
-            if (it != g_adjusted_texture_cache.entries.end() && it->second.adjust == layer.preview_adjust &&
-                it->second.source.lock() == layer.image_data) {
-                result        = it->second.texture;
-                have_adjusted = true;
-            }
-        }
-        if (!have_adjusted) {
-            result = apply_texture_adjustments(result, layer.preview_adjust);
-            std::lock_guard<std::mutex> lock(g_adjusted_texture_cache.mutex);
-            auto &entries = g_adjusted_texture_cache.entries;
-            for (auto it = entries.begin(); it != entries.end();)
-                it = it->second.source.expired() ? entries.erase(it) : std::next(it);
-            entries[key] = { std::weak_ptr<const std::vector<unsigned char>>(layer.image_data),
-                             layer.preview_adjust, result };
-        }
-    }
-
     // Smoothing radius scales with the texture so the same slider value blurs the same *fraction* of
     // the image whatever resolution it came in at, and stays continuous in the slider - see
     // smooth_height_pixels(). The cap is a cost limit, not part of the mapping: the blur is
@@ -397,7 +348,7 @@ DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer
             std::lock_guard<std::mutex> lock(g_smoothed_texture_cache.mutex);
             auto it = g_smoothed_texture_cache.entries.find(key);
             if (it != g_smoothed_texture_cache.entries.end() && it->second.smoothing == layer.smoothing &&
-                it->second.adjust == layer.preview_adjust && it->second.source.lock() == layer.image_data)
+                it->second.source.lock() == layer.image_data)
                 return it->second.texture;
         }
         const float span   = 0.05f * float(std::min(result.width, result.height));
@@ -421,70 +372,12 @@ DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer
         auto &entries = g_smoothed_texture_cache.entries;
         for (auto it = entries.begin(); it != entries.end();)
             it = it->second.source.expired() ? entries.erase(it) : std::next(it);
-        entries[key] = { std::weak_ptr<const std::vector<unsigned char>>(layer.image_data), layer.smoothing,
-                         layer.preview_adjust, result };
+        entries[key] = { std::weak_ptr<const std::vector<unsigned char>>(layer.image_data), layer.smoothing, result };
     }
     return result;
 }
 
 namespace {
-// Fraction of the short side that TextureAdjustments::blur == 1 blurs over, and the cost cap on it.
-// Deliberately the same pair decode_height_texture() uses for the Smoothing slider - see
-// adjustment_blur_radius().
-constexpr float SOURCE_BLUR_SPAN   = 0.05f;
-constexpr float SOURCE_BLUR_MAX_PX = 48.f;
-
-// Radius of the unsharp mask's blurred reference, in texels. Small and only mildly resolution-dependent:
-// a sharpen is meant to act on the finest detail the image holds, so its radius tracks the texel grid
-// rather than the picture's size. 1024x1024 gives ~2 texels, the usual photo-editor default.
-float unsharp_radius(int width, int height)
-{
-    return std::max(1.f, 0.002f * float(std::min(width, height)));
-}
-
-// Brightness as a *lift* toward white (or toward black) rather than an additive offset: positive b maps
-// v to v + b*(1 - v), negative to v*(1 + b). Both reach the endpoint exactly at |b| == 1 while staying
-// monotonic and non-clipping in between, which an additive shift does not - it drives a whole region to
-// a flat 255 and, because this image is also the height map, that region bakes as flat relief rather
-// than as bright relief. Keeping the curve injective keeps the detail in it.
-float apply_brightness(float v, float b)
-{
-    return b >= 0.f ? v + b * (1.f - v) : v * (1.f + b);
-}
-
-// Contrast about the 0.5 pivot. Gain is 1/(1-c) going up (c == 1 would be an infinite-slope threshold, so
-// the caller's clamp keeps it finite) and 1+c going down, reaching a flat mid-grey at c == -1.
-float apply_contrast(float v, float c)
-{
-    const float gain = c >= 0.f ? 1.f / std::max(1e-3f, 1.f - c) : 1.f + c;
-    return (v - 0.5f) * gain + 0.5f;
-}
-
-// Blur then sharpen one 8-bit channel in place. Shared by the grayscale path and by each of a colour
-// image's three channels, so every channel gets the identical spatial treatment and a colour image's
-// hue cannot shift just because its channels were filtered differently.
-void adjust_channel_spatial(std::vector<uint8_t> &channel, int width, int height, float blur, float sharpness)
-{
-    if (blur > 0.f)
-        smooth_height_pixels(channel, width, height, adjustment_blur_radius(blur, width, height));
-
-    if (sharpness <= 0.f)
-        return;
-
-    // Unsharp mask: push each texel away from its local average by `amount` times the difference. The
-    // blurred reference is a copy, so the sharpen reads the un-sharpened neighbourhood everywhere rather
-    // than its own partly-written output.
-    std::vector<uint8_t> base = channel;
-    smooth_height_pixels(base, width, height, unsharp_radius(width, height));
-    const float amount = 1.5f * std::clamp(sharpness, 0.f, 1.f);
-    tbb::parallel_for(tbb::blocked_range<size_t>(0, channel.size()), [&](const tbb::blocked_range<size_t> &r) {
-        for (size_t i = r.begin(); i < r.end(); ++i) {
-            const float v = float(channel[i]) + amount * (float(channel[i]) - float(base[i]));
-            channel[i]    = uint8_t(std::lround(std::clamp(v, 0.f, 255.f)));
-        }
-    });
-}
-
 struct TextureDetailCache
 {
     std::mutex mutex;
@@ -493,150 +386,6 @@ struct TextureDetailCache
 TextureDetailCache g_texture_detail_cache;
 } // namespace
 
-float adjustment_blur_radius(float blur, int width, int height)
-{
-    if (blur <= 0.f || width <= 0 || height <= 0)
-        return 0.f;
-    const float span = SOURCE_BLUR_SPAN * float(std::min(width, height));
-    return std::clamp(blur, 0.f, 1.f) * std::min(span, SOURCE_BLUR_MAX_PX);
-}
-
-DecodedHeightTexture downscale_height_texture(const DecodedHeightTexture &src, int max_px)
-{
-    if (src.empty() || max_px <= 0 || (src.width <= max_px && src.height <= max_px))
-        return src;
-
-    const int  scale = std::max(1, (std::max(src.width, src.height) + max_px - 1) / max_px);
-    const int  w     = std::max(1, src.width / scale);
-    const int  h     = std::max(1, src.height / scale);
-    const bool color = src.has_color();
-
-    DecodedHeightTexture out;
-    out.width  = w;
-    out.height = h;
-    out.pixels.resize(size_t(w) * size_t(h));
-    if (color)
-        out.rgb.resize(size_t(w) * size_t(h) * 3);
-
-    tbb::parallel_for(tbb::blocked_range<int>(0, h), [&](const tbb::blocked_range<int> &r) {
-        for (int y = r.begin(); y < r.end(); ++y)
-            for (int x = 0; x < w; ++x) {
-                // The source block this destination texel covers. The max() keeps the block non-empty
-                // when rounding would otherwise collapse it.
-                const int x0 = x * src.width / w, x1 = std::max(x0 + 1, (x + 1) * src.width / w);
-                const int y0 = y * src.height / h, y1 = std::max(y0 + 1, (y + 1) * src.height / h);
-                uint32_t  sum_h = 0, sum_c[3] = { 0, 0, 0 }, n = 0;
-                for (int sy = y0; sy < y1 && sy < src.height; ++sy)
-                    for (int sx = x0; sx < x1 && sx < src.width; ++sx, ++n) {
-                        const size_t si = size_t(sy) * size_t(src.width) + size_t(sx);
-                        sum_h += src.pixels[si];
-                        if (color)
-                            for (int c = 0; c < 3; ++c)
-                                sum_c[c] += src.rgb[si * 3 + size_t(c)];
-                    }
-                const size_t di = size_t(y) * size_t(w) + size_t(x);
-                out.pixels[di]  = n > 0 ? uint8_t(sum_h / n) : 0;
-                if (color)
-                    for (int c = 0; c < 3; ++c)
-                        out.rgb[di * 3 + size_t(c)] = n > 0 ? uint8_t(sum_c[c] / n) : 0;
-            }
-    });
-    return out;
-}
-
-DecodedHeightTexture apply_texture_adjustments(const DecodedHeightTexture &src, const TextureAdjustments &adj)
-{
-    DecodedHeightTexture out = src;
-    if (src.empty() || adj.identity())
-        return out;
-
-    const int    w = out.width;
-    const int    h = out.height;
-    const size_t n = size_t(w) * size_t(h);
-
-    const float brightness = std::clamp(adj.brightness, -1.f, 1.f);
-    // Short of 1, so apply_contrast()'s gain stays finite; at this value it is already a 1000x slope,
-    // i.e. a threshold in all but name.
-    const float contrast   = std::clamp(adj.contrast, -1.f, 0.999f);
-    const float blur       = std::clamp(adj.blur, 0.f, 1.f);
-    const float sharpness  = std::clamp(adj.sharpness, 0.f, 1.f);
-
-    // The tonal pass: a 256-entry lookup table, because brightness and contrast are the same scalar
-    // curve for every texel and every channel. Building it once beats evaluating two curves a few
-    // million times, and it is what keeps this pass off the panel's critical path.
-    std::array<uint8_t, 256> tone{};
-    for (int i = 0; i < 256; ++i) {
-        float v = float(i) / 255.f;
-        v       = apply_brightness(v, brightness);
-        v       = apply_contrast(v, contrast);
-        tone[size_t(i)] = uint8_t(std::lround(std::clamp(v, 0.f, 1.f) * 255.f));
-    }
-
-    if (!out.has_color()) {
-        // Grayscale: one channel, and hue has nothing to turn.
-        tbb::parallel_for(tbb::blocked_range<size_t>(0, n), [&](const tbb::blocked_range<size_t> &r) {
-            for (size_t i = r.begin(); i < r.end(); ++i)
-                out.pixels[i] = tone[out.pixels[i]];
-        });
-        adjust_channel_spatial(out.pixels, w, h, blur, sharpness);
-        return out;
-    }
-
-    // Colour: tone each channel through the same table, then rotate the hue about the luminance axis.
-    //
-    // The rotation is feColorMatrix's hueRotate matrix (SVG filters), which holds Rec.709 luma fixed.
-    // The height below is taken with decode_height_texture()'s Rec.601 coefficients instead, so a hue
-    // turn is not perfectly height-neutral - a few levels at full saturation. Reconciling the two would
-    // mean a different rotation than every other tool's, which is the worse trade: the user is watching
-    // the colour, and the height follows the colour by construction either way.
-    const float  theta = adj.hue_deg * float(M_PI) / 180.f;
-    const float  c     = std::cos(theta);
-    const float  s     = std::sin(theta);
-    const float  m[9]  = {
-        0.213f + c * 0.787f - s * 0.213f, 0.715f - c * 0.715f - s * 0.715f, 0.072f - c * 0.072f + s * 0.928f,
-        0.213f - c * 0.213f + s * 0.143f, 0.715f + c * 0.285f + s * 0.140f, 0.072f - c * 0.072f - s * 0.283f,
-        0.213f - c * 0.213f - s * 0.787f, 0.715f - c * 0.715f + s * 0.715f, 0.072f + c * 0.928f + s * 0.072f,
-    };
-    const bool turn_hue = adj.hue_deg != 0.f;
-
-    tbb::parallel_for(tbb::blocked_range<size_t>(0, n), [&](const tbb::blocked_range<size_t> &r) {
-        for (size_t i = r.begin(); i < r.end(); ++i) {
-            const float rr = float(tone[out.rgb[i * 3]]);
-            const float gg = float(tone[out.rgb[i * 3 + 1]]);
-            const float bb = float(tone[out.rgb[i * 3 + 2]]);
-            const float nr = turn_hue ? m[0] * rr + m[1] * gg + m[2] * bb : rr;
-            const float ng = turn_hue ? m[3] * rr + m[4] * gg + m[5] * bb : gg;
-            const float nb = turn_hue ? m[6] * rr + m[7] * gg + m[8] * bb : bb;
-            out.rgb[i * 3]     = uint8_t(std::lround(std::clamp(nr, 0.f, 255.f)));
-            out.rgb[i * 3 + 1] = uint8_t(std::lround(std::clamp(ng, 0.f, 255.f)));
-            out.rgb[i * 3 + 2] = uint8_t(std::lround(std::clamp(nb, 0.f, 255.f)));
-        }
-    });
-
-    // The spatial pass wants one channel at a time (smooth_height_pixels() is a single-channel blur, and
-    // reusing it is what keeps this consistent with Smoothing), so de-interleave, filter, re-interleave.
-    if (blur > 0.f || sharpness > 0.f) {
-        std::vector<uint8_t> channel(n);
-        for (int ch = 0; ch < 3; ++ch) {
-            for (size_t i = 0; i < n; ++i)
-                channel[i] = out.rgb[i * 3 + size_t(ch)];
-            adjust_channel_spatial(channel, w, h, blur, sharpness);
-            for (size_t i = 0; i < n; ++i)
-                out.rgb[i * 3 + size_t(ch)] = channel[i];
-        }
-    }
-
-    // Height is the luminance of the colour that came out, not the toned luminance of the colour that
-    // went in: the two differ once hue rotation or a per-channel clamp has moved the channels around,
-    // and a height that disagrees with the colour it is stored next to is the bug this avoids.
-    tbb::parallel_for(tbb::blocked_range<size_t>(0, n), [&](const tbb::blocked_range<size_t> &r) {
-        for (size_t i = r.begin(); i < r.end(); ++i)
-            out.pixels[i] = uint8_t(std::lround(0.299 * out.rgb[i * 3] + 0.587 * out.rgb[i * 3 + 1] +
-                                                0.114 * out.rgb[i * 3 + 2]));
-    });
-    return out;
-}
-
 TextureDetail analyze_texture_detail(const TextureDisplacementLayer &layer)
 {
     TextureDetail out;
@@ -1923,6 +1672,165 @@ std::vector<Vec2f> compute_lscm_corner_uvs(const indexed_triangle_set &patch, co
     return corner;
 }
 
+// Barycentric weights of `p` inside triangle (a, b, c), as the pair that belongs with the edges
+// (b - a) and (c - a): p ~= (1 - w1 - w2) * a + w1 * b + w2 * c. `p` is projected onto the triangle's
+// plane, so a point a hair off the surface still reports the weights of its foot point. A degenerate
+// triangle reports its centroid, the only coordinate that means anything there.
+static void barycentric_weights(const Vec3f &a, const Vec3f &b, const Vec3f &c, const Vec3f &p, float &w1, float &w2)
+{
+    const Vec3f e0 = b - a, e1 = c - a, ep = p - a;
+    const float d00 = e0.dot(e0), d01 = e0.dot(e1), d11 = e1.dot(e1), dp0 = ep.dot(e0), dp1 = ep.dot(e1);
+    const float den = d00 * d11 - d01 * d01;
+    if (std::abs(den) <= 1e-20f) {
+        w1 = w2 = 1.f / 3.f;
+        return;
+    }
+    w1 = (d11 * dp0 - d01 * dp1) / den;
+    w2 = (d00 * dp1 - d01 * dp0) / den;
+}
+
+std::vector<Vec2f> compute_model_corner_uvs(const indexed_triangle_set &base_mesh,
+                                            const std::vector<Vec2f>   &model_uv,
+                                            const indexed_triangle_set &patch,
+                                            const std::vector<int>     &patch_source)
+{
+    if (patch.indices.empty() || model_uv.size() != base_mesh.indices.size() * 3 ||
+        patch_source.size() != patch.indices.size())
+        return {};
+
+    std::vector<Vec2f> corner(patch.indices.size() * 3, Vec2f::Zero());
+    for (size_t j = 0; j < patch.indices.size(); ++j) {
+        const int S = patch_source[j];
+        if (S < 0 || size_t(S) >= base_mesh.indices.size())
+            continue; // no source triangle: leave (0, 0), which the callers read as "no placement"
+        const stl_triangle_vertex_indices &src = base_mesh.indices[size_t(S)];
+        const Vec3f &a = base_mesh.vertices[size_t(src[0])];
+        const Vec3f &b = base_mesh.vertices[size_t(src[1])];
+        const Vec3f &c = base_mesh.vertices[size_t(src[2])];
+        const Vec2f *uv = &model_uv[size_t(S) * 3];
+        const stl_triangle_vertex_indices &tri = patch.indices[j];
+        for (int k = 0; k < 3; ++k) {
+            // An unsplit patch triangle is its source triangle, so its corners land exactly on a, b
+            // and c and this reproduces their uvs unchanged; a sub-triangle the brush cut gets the
+            // interpolated coordinate, which is the whole point of going through the barycentric.
+            float w1 = 0.f, w2 = 0.f;
+            barycentric_weights(a, b, c, patch.vertices[size_t(tri[k])], w1, w2);
+            corner[j * 3 + size_t(k)] = (1.f - w1 - w2) * uv[0] + w1 * uv[1] + w2 * uv[2];
+        }
+    }
+    return corner;
+}
+
+std::vector<Vec2f> collapse_corner_uvs(const indexed_triangle_set &patch, const std::vector<Vec2f> &corner)
+{
+    if (patch.indices.empty() || corner.size() != patch.indices.size() * 3)
+        return {};
+
+    std::vector<Vec2f> per_vertex(patch.vertices.size(), Vec2f::Zero());
+    std::vector<char>  seen(patch.vertices.size(), 0);
+    for (size_t j = 0; j < patch.indices.size(); ++j)
+        for (int k = 0; k < 3; ++k) {
+            const int vi = patch.indices[j][k];
+            if (vi < 0 || size_t(vi) >= per_vertex.size() || seen[size_t(vi)])
+                continue;
+            seen[size_t(vi)]       = 1;
+            per_vertex[size_t(vi)] = corner[j * 3 + size_t(k)];
+        }
+    return per_vertex;
+}
+
+std::vector<Vec2f> transfer_uv_channel(const indexed_triangle_set &src_mesh,
+                                       const std::vector<Vec2f>   &src_uv,
+                                       const indexed_triangle_set &dst_mesh,
+                                       float                       max_distance)
+{
+    if (src_mesh.indices.empty() || dst_mesh.indices.empty() || src_uv.size() != src_mesh.indices.size() * 3)
+        return {};
+
+    const AABBTreeIndirect::Tree3f tree =
+        AABBTreeIndirect::build_aabb_tree_over_indexed_triangle_set(src_mesh.vertices, src_mesh.indices);
+    const float limit2 = max_distance >= 0.f ? max_distance * max_distance : std::numeric_limits<float>::max();
+
+    std::vector<Vec2f> out(dst_mesh.indices.size() * 3, Vec2f::Zero());
+    tbb::parallel_for(tbb::blocked_range<size_t>(0, dst_mesh.indices.size()),
+                      [&](const tbb::blocked_range<size_t> &range) {
+        for (size_t j = range.begin(); j < range.end(); ++j) {
+            const stl_triangle_vertex_indices &tri = dst_mesh.indices[j];
+            for (int k = 0; k < 3; ++k) {
+                const Vec3f &p = dst_mesh.vertices[size_t(tri[k])];
+                size_t       hit = 0;
+                Vec3f        foot;
+                const float  d2 = AABBTreeIndirect::squared_distance_to_indexed_triangle_set(
+                    src_mesh.vertices, src_mesh.indices, tree, p, hit, foot);
+                if (d2 < 0.f || d2 > limit2 || hit >= src_mesh.indices.size())
+                    continue; // nowhere near the source surface: (0, 0), as documented
+                const stl_triangle_vertex_indices &st = src_mesh.indices[hit];
+                float w1 = 0.f, w2 = 0.f;
+                barycentric_weights(src_mesh.vertices[size_t(st[0])], src_mesh.vertices[size_t(st[1])],
+                                    src_mesh.vertices[size_t(st[2])], foot, w1, w2);
+                const Vec2f *uv        = &src_uv[hit * 3];
+                out[j * 3 + size_t(k)] = (1.f - w1 - w2) * uv[0] + w1 * uv[1] + w2 * uv[2];
+            }
+        }
+    });
+    return out;
+}
+
+std::vector<uint8_t> transfer_facet_paint(const indexed_triangle_set                    &src_mesh,
+                                         const TriangleSelector::TriangleSplittingData &src_paint,
+                                         const indexed_triangle_set                    &dst_mesh)
+{
+    if (src_mesh.indices.empty() || dst_mesh.indices.empty() || src_paint.bitstream.empty())
+        return {};
+
+    const TriangleMesh src(src_mesh);
+    TriangleSelector   selector(src);
+    selector.deserialize(src_paint, false);
+
+    // Every sub-triangle of the source, each carrying its own state - NONE included, so the soup
+    // covers the whole surface and a foot point always lands on something. One soup rather than one
+    // tree per state: a foot point has one nearest triangle, and that triangle's state is the answer.
+    std::vector<indexed_triangle_set> per_state;
+    selector.get_facets(per_state);
+    indexed_triangle_set soup;
+    std::vector<uint8_t> label;
+    for (size_t st = 0; st < per_state.size(); ++st) {
+        const indexed_triangle_set &part = per_state[st];
+        if (part.indices.empty())
+            continue;
+        const int base = int(soup.vertices.size());
+        soup.vertices.insert(soup.vertices.end(), part.vertices.begin(), part.vertices.end());
+        for (const stl_triangle_vertex_indices &t : part.indices) {
+            soup.indices.emplace_back(t[0] + base, t[1] + base, t[2] + base);
+            label.push_back(uint8_t(st));
+        }
+    }
+    if (soup.indices.empty())
+        return {};
+
+    const AABBTreeIndirect::Tree3f tree =
+        AABBTreeIndirect::build_aabb_tree_over_indexed_triangle_set(soup.vertices, soup.indices);
+
+    std::vector<uint8_t> out(dst_mesh.indices.size(), 0);
+    tbb::parallel_for(tbb::blocked_range<size_t>(0, dst_mesh.indices.size()),
+                      [&](const tbb::blocked_range<size_t> &range) {
+        for (size_t j = range.begin(); j < range.end(); ++j) {
+            const stl_triangle_vertex_indices &t = dst_mesh.indices[j];
+            // The centroid, not a corner: a facet takes one state, and its middle is the point that
+            // is inside it whatever the triangle looks like.
+            const Vec3f centroid = (dst_mesh.vertices[size_t(t[0])] + dst_mesh.vertices[size_t(t[1])] +
+                                    dst_mesh.vertices[size_t(t[2])]) / 3.f;
+            size_t      hit = 0;
+            Vec3f       foot;
+            const float d2 = AABBTreeIndirect::squared_distance_to_indexed_triangle_set(soup.vertices, soup.indices,
+                                                                                        tree, centroid, hit, foot);
+            if (d2 >= 0.f && hit < label.size())
+                out[j] = label[hit];
+        }
+    });
+    return out;
+}
+
 namespace {
 // apply_uv_transform()'s per-layer constants, worked out once. Triplanar sampling runs the transform
 // three times per point, and recomputing the rotation's cos/sin and the tiling reciprocal on every one
@@ -1932,13 +1840,16 @@ struct UVTransform
     float scale, cs, sn, aspect;
     Vec2f offset;
 
-    UVTransform(const TextureDisplacementLayer &layer, float aspect_)
+    // `normalized_uv` drops the two steps that only mean something for a coordinate measured on the
+    // model - the millimetre tiling scale and the non-square aspect correction - and keeps the
+    // rotation and offset. See apply_uv_transform(); TextureProjectionMethod::ModelUV is what needs it.
+    UVTransform(const TextureDisplacementLayer &layer, float aspect_, bool normalized_uv = false)
     {
-        scale = (layer.tiling_scale > 1e-6f) ? (1.f / layer.tiling_scale) : 1.f;
+        scale = (normalized_uv || layer.tiling_scale <= 1e-6f) ? 1.f : (1.f / layer.tiling_scale);
         const float rad = layer.rotation_deg * float(M_PI) / 180.f;
         cs     = std::cos(rad);
         sn     = std::sin(rad);
-        aspect = aspect_;
+        aspect = normalized_uv ? 1.f : aspect_;
         offset = layer.offset;
     }
     Vec2f operator()(const Vec2f &planar) const
@@ -1963,9 +1874,11 @@ inline Vec3f triplanar_weights(const Vec3f &normal)
 }
 } // namespace
 
-Vec2f apply_uv_transform(const Vec2f &planar, const TextureDisplacementLayer &layer, float aspect)
+Vec2f apply_uv_transform(const Vec2f &planar, const TextureDisplacementLayer &layer, float aspect, bool normalized_uv)
 {
-    const float scale = (layer.tiling_scale > 1e-6f) ? (1.f / layer.tiling_scale) : 1.f;
+    // A uv that is already normalized has no millimetre scale to divide by and no aspect to correct -
+    // see the header. UVTransform does the same, and the two must stay in step.
+    const float scale = (normalized_uv || layer.tiling_scale <= 1e-6f) ? 1.f : (1.f / layer.tiling_scale);
     const Vec2f scaled = planar * scale;
 
     const float rad = layer.rotation_deg * float(M_PI) / 180.f;
@@ -1983,7 +1896,7 @@ Vec2f apply_uv_transform(const Vec2f &planar, const TextureDisplacementLayer &la
     // Applied after the rotation, not before: scaling one axis of an already-rotated coordinate is a
     // shear, and doing it the other way round would make "Rotation" skew the pattern instead of
     // turning it.
-    if (aspect > 0.f && aspect != 1.f)
+    if (!normalized_uv && aspect > 0.f && aspect != 1.f)
         rotated.y() *= aspect;
 
     return rotated + layer.offset;
@@ -2008,6 +1921,9 @@ float blend_displacement(float accumulated, float value, TextureBlendMode mode)
                                                                         value;
         return accumulated / divisor;
     }
+    // Replaces instead of combining, so `accumulated` is deliberately unused: whatever the layers
+    // below put here is gone where this one is painted.
+    case TextureBlendMode::Override: return value;
     case TextureBlendMode::Add:
     default: return accumulated + value;
     }
@@ -2037,14 +1953,21 @@ float sample_layer_height(const DecodedHeightTexture &texture, const TextureDisp
     // apply_uv_transform()). Every projection except the projective "from view" one funnels through
     // here, so this one line is what makes them all aspect-correct.
     const float       aspect = (texture.height > 0) ? float(texture.width) / float(texture.height) : 1.f;
-    const UVTransform xf(layer, aspect);
+    // A ModelUV layer's precomputed uv is the model's own, already normalized; every other coordinate
+    // reaching the transform - the unwrap's, and every analytic projection's - is in millimetres. The
+    // `lscm_uv` test is what keeps the two apart: a ModelUV layer with no channel gets none, falls
+    // through to the millimetre methods below, and must be scaled like them.
+    const bool        normalized_uv = layer.projection_method == TextureProjectionMethod::ModelUV &&
+                                      lscm_uv != nullptr;
+    const UVTransform xf(layer, aspect, normalized_uv);
     auto sample_at = [&](const Vec2f &planar) {
         return texture.sample(xf(planar), layer.tile_enabled, layer.tile_method);
     };
 
-    // Precomputed per-patch LSCM solve wins over the layer's own method (see the header): the
-    // caller only passes it when the patch actually parameterized successfully, so a patch that
-    // failed to unwrap falls through to the analytic methods below as its documented fallback.
+    // A precomputed per-patch uv - the LSCM solve, or the model's own channel - wins over the layer's
+    // own method (see the header): the caller only passes it when the patch actually has one, so a
+    // patch that failed to unwrap, or a volume with no UV channel, falls through to the analytic
+    // methods below as its documented fallback.
     if (lscm_uv != nullptr)
         return sample_at(*lscm_uv);
 
@@ -2067,7 +1990,8 @@ float sample_layer_height(const DecodedHeightTexture &texture, const TextureDisp
         // Flat projection onto the captured projector plane. Single-valued per point, so unlike
         // blended triplanar it is one sample, and it is what "project from view" places.
         return sample_at(Vec2f(position.dot(layer.view_project_right), position.dot(layer.view_project_up)));
-    case TextureProjectionMethod::LSCM: // no usable unwrap for this patch - fall back to Triplanar
+    case TextureProjectionMethod::LSCM:    // no usable unwrap for this patch - fall back to Triplanar
+    case TextureProjectionMethod::ModelUV: // the volume carries no UV channel - same fallback
     case TextureProjectionMethod::Triplanar:
     default: break;
     }
@@ -2102,8 +2026,12 @@ bool sample_layer_color(const DecodedHeightTexture &texture, const TextureDispla
     // the two differ in what "nothing here" means. Height returns 0, which is a perfectly good height
     // (no displacement); colour has no such neutral value - black is a colour - so every path that
     // returns 0 there has to report false here instead, and the caller leaves the triangle uncoloured.
-    const float       aspect = (texture.height > 0) ? float(texture.width) / float(texture.height) : 1.f;
-    const UVTransform xf(layer, aspect);
+    const float       aspect        = (texture.height > 0) ? float(texture.width) / float(texture.height) : 1.f;
+    // Same reasoning as sample_layer_height(), and it has to match it exactly or a layer's colour and
+    // its relief would be read from different places in the image.
+    const bool        normalized_uv = layer.projection_method == TextureProjectionMethod::ModelUV &&
+                                      lscm_uv != nullptr;
+    const UVTransform xf(layer, aspect, normalized_uv);
     auto sample_at = [&](const Vec2f &planar) {
         return texture.sample_color(xf(planar), layer.tile_enabled, layer.tile_method);
     };
@@ -2117,6 +2045,8 @@ bool sample_layer_color(const DecodedHeightTexture &texture, const TextureDispla
     };
 
     if (lscm_uv != nullptr) {
+        // The coverage test goes through the same transform, so an untiled ModelUV layer is "there"
+        // exactly where the model's own uv lands inside the image.
         if (!covered(*lscm_uv))
             return false;
         out = sample_at(*lscm_uv);
@@ -2156,7 +2086,8 @@ bool sample_layer_color(const DecodedHeightTexture &texture, const TextureDispla
             out = sample_at(p);
             return true;
         }
-    case TextureProjectionMethod::LSCM: // no usable unwrap for this patch - fall back to Triplanar
+    case TextureProjectionMethod::LSCM:    // no usable unwrap for this patch - fall back to Triplanar
+    case TextureProjectionMethod::ModelUV: // the volume carries no UV channel - same fallback
     case TextureProjectionMethod::Triplanar:
     default: break;
     }
@@ -2461,9 +2392,10 @@ indexed_triangle_set build_texture_displacement_v2(const indexed_triangle_set
                                                    const TextureColorRequest                   *color,
                                                    bool                                         flip_normals,
                                                    BakeStageRecorder                           *debug,
-                                                   TextureBakeStats                            *stats)
+                                                   TextureBakeStats                            *stats,
+                                                   const std::vector<Vec2f>                    *model_uv)
 {
-    HeightFieldSampler combined = make_combined_displacement_sampler(mesh, layers, facets_data);
+    HeightFieldSampler combined = make_combined_displacement_sampler(mesh, layers, facets_data, model_uv);
     if (!combined)
         return mesh; // nothing decodable to displace with
 
@@ -2633,7 +2565,8 @@ indexed_triangle_set build_texture_displacement_v2(const indexed_triangle_set
     // part of it (half a tile in the neighbour's colour, a tile edge that wanders).
     const bool              want_color = color != nullptr && color->out_triangle != nullptr && bool(color->quantize);
     const ColorFieldSampler color_sampler =
-        want_color ? make_combined_color_sampler(mesh, layers, facets_data, color->quantize, color->quantize_pure) : ColorFieldSampler{};
+        want_color ? make_combined_color_sampler(mesh, layers, facets_data, color->quantize, color->quantize_pure, model_uv) :
+                     ColorFieldSampler{};
     //
     // The *palette* index, not the printed filament. The decimation treats any edge whose two faces
     // differ as a crease (TextureBakeDecimate.cpp), so it must only ever see where the **perceived**
@@ -2765,7 +2698,8 @@ static indexed_triangle_set build_texture_displacement_in_place(
     const TextureColorRequest                   *color,
     bool                                         flip_normals,
     BakeStageRecorder                           *debug,
-    TextureBakeStats                            *stats)
+    TextureBakeStats                            *stats,
+    const std::vector<Vec2f>                    *model_uv)
 {
     // The classic path moves the vertices the mesh already has, so there is no budget to report on.
     (void) stats;
@@ -2802,7 +2736,7 @@ static indexed_triangle_set build_texture_displacement_in_place(
 
     if (options.pipeline_v2)
         return build_texture_displacement_v2(mesh, layers, facets_data, options, progress, color, flip_normals,
-                                             debug, stats);
+                                             debug, stats, model_uv);
 
     // Layers are combined in slot order, like stacked layers in an image editor: each one folds its
     // own displacement into the running total via its blend mode (see TextureBlendMode).
@@ -2920,13 +2854,19 @@ static indexed_triangle_set build_texture_displacement_in_place(
         selector_dirty = true;
 
         const bool       color_this_layer = want_color && layer->color_enabled;
+        // The model's own channel is per base-mesh *triangle*, so reading it needs to know which base
+        // triangle each (possibly brush-split) patch triangle came from - the colour pass's map, asked
+        // for here as well.
+        const bool       model_uv_layer   = layer->projection_method == TextureProjectionMethod::ModelUV &&
+                                            model_uv != nullptr && model_uv->size() == mesh.indices.size() * 3;
         // A flat-colour image is matched against the filaments alone (see TextureColorRequest).
         const ColorQuantizeFn &layer_quantize =
             (color_this_layer && color->quantize_pure && analyze_texture_detail(*layer).flat_colors) ? color->quantize_pure
                                                                                                      : color->quantize;
-        std::vector<int> patch_source; // sub-triangle -> base mesh triangle, only built when colouring
+        std::vector<int> patch_source; // sub-triangle -> base mesh triangle; built when colouring or mapping by ModelUV
         const indexed_triangle_set patch =
-            selector.get_facets_strict(EnforcerBlockerType::ENFORCER, color_this_layer ? &patch_source : nullptr);
+            selector.get_facets_strict(EnforcerBlockerType::ENFORCER,
+                                       (color_this_layer || model_uv_layer) ? &patch_source : nullptr);
         if (patch.indices.empty())
             continue;
         // get_facets_strict() returns the same vertex array whichever state is asked for (only the
@@ -2957,18 +2897,25 @@ static indexed_triangle_set build_texture_displacement_in_place(
         // A real unwrap of the whole patch, computed once here rather than per vertex - it is a
         // per-chart solve over the whole patch, not a per-point formula. Cached, so repeating this
         // for every slider tweak costs a hash rather than a re-solve (see compute_patch_unwrap()).
-        const std::vector<Vec2f> lscm_uvs = (layer->projection_method == TextureProjectionMethod::LSCM) ?
+        // ModelUV takes its corners from the volume's own channel instead of solving anything, and
+        // collapses them to one per vertex the same way the unwrap does.
+        const std::vector<Vec2f> model_corner_uvs = model_uv_layer ?
+                                                        compute_model_corner_uvs(mesh, *model_uv, patch, patch_source) :
+                                                        std::vector<Vec2f>{};
+        const std::vector<Vec2f> patch_uvs = model_uv_layer ? collapse_corner_uvs(patch, model_corner_uvs) :
+                                             (layer->projection_method == TextureProjectionMethod::LSCM) ?
                                                  compute_lscm_uvs(patch, *layer) :
                                                  std::vector<Vec2f>{};
         // The colour pass below samples per *triangle*, so it takes the per-corner unwrap instead: the
         // per-vertex collapse above would hand a triangle at a seam the island layout did not join its
         // neighbour's placement, painting one triangle per face from the wrong part of the texture.
-        // (The displacement itself stays on lscm_uvs - a vertex has one position, so one height.)
-        const std::vector<Vec2f> lscm_corner_uvs = (layer->projection_method == TextureProjectionMethod::LSCM) ?
+        // (The displacement itself stays on patch_uvs - a vertex has one position, so one height.)
+        const std::vector<Vec2f> patch_corner_uvs = model_uv_layer ? model_corner_uvs :
+                                                    (layer->projection_method == TextureProjectionMethod::LSCM) ?
                                                         compute_lscm_corner_uvs(patch, *layer) :
                                                         std::vector<Vec2f>{};
-        const bool               corner_uv_ok    = !lscm_corner_uvs.empty() &&
-                                                   lscm_corner_uvs.size() == patch.indices.size() * 3;
+        const bool               corner_uv_ok     = !patch_corner_uvs.empty() &&
+                                                    patch_corner_uvs.size() == patch.indices.size() * 3;
 
         // Colour, if this layer carries any. Area-weighted over each base triangle's *painted* part,
         // so a triangle the brush only clipped a corner off takes the colour of that corner rather
@@ -2998,7 +2945,7 @@ static indexed_triangle_set build_texture_displacement_in_place(
                     // the per-vertex height sampling uses, evaluated at the centroid instead.
                     Vec3f n = Vec3f::Zero();
                     Vec2f uv = Vec2f::Zero();
-                    bool  have_uv = !lscm_uvs.empty();
+                    bool  have_uv = !patch_uvs.empty();
                     for (int k = 0; k < 3; ++k) {
                         const int vi = t[k];
                         if (vi < int(vertex_normals.size()))
@@ -3006,9 +2953,9 @@ static indexed_triangle_set build_texture_displacement_in_place(
                         if (!have_uv)
                             continue;
                         if (corner_uv_ok)
-                            uv += lscm_corner_uvs[j * 3 + size_t(k)];
-                        else if (size_t(vi) < lscm_uvs.size())
-                            uv += lscm_uvs[size_t(vi)];
+                            uv += patch_corner_uvs[j * 3 + size_t(k)];
+                        else if (size_t(vi) < patch_uvs.size())
+                            uv += patch_uvs[size_t(vi)];
                         else
                             have_uv = false;
                     }
@@ -3082,7 +3029,7 @@ static indexed_triangle_set build_texture_displacement_in_place(
                           [&](const tbb::blocked_range<size_t> &range) {
             for (size_t k = range.begin(); k < range.end(); ++k) {
                 const size_t vi      = size_t(layer_vertices[k]);
-                const Vec2f *lscm_uv = lscm_uvs.empty() ? nullptr : &lscm_uvs[vi];
+                const Vec2f *lscm_uv = patch_uvs.empty() ? nullptr : &patch_uvs[vi];
                 const float  h       = sample_layer_height(height, *layer, mesh.vertices[vi], vertex_normals[vi],
                                                             patch_centroid, patch_axis, lscm_uv);
                 // midlevel is the height that means "stay put", so anything below it displaces
@@ -3215,7 +3162,8 @@ indexed_triangle_set build_texture_displacement(const indexed_triangle_set
                                                  const TextureColorRequest                   *color,
                                                  const Transform3d                           &volume_to_world,
                                                  BakeStageRecorder                           *debug,
-                                                 TextureBakeStats                            *stats)
+                                                 TextureBakeStats                            *stats,
+                                                 const std::vector<Vec2f>                    *model_uv)
 {
     // An untransformed volume on an untransformed instance is by far the common case, and the round
     // trip costs two matrix multiplies per vertex on a mesh that can carry millions of them - so take
@@ -3225,7 +3173,7 @@ indexed_triangle_set build_texture_displacement(const indexed_triangle_set
     const Transform3d frame = texture_displacement_bake_frame(volume_to_world);
     if (frame.matrix().isApprox(Transform3d::Identity().matrix()))
         return build_texture_displacement_in_place(base_mesh, layers, facets_data, options, progress, color,
-                                                   false, debug, stats);
+                                                   false, debug, stats, model_uv);
 
     const Transform3d to_local = frame.inverse();
     // A mirroring placement leaves the positions correct but every winding-derived normal pointing
@@ -3239,8 +3187,10 @@ indexed_triangle_set build_texture_displacement(const indexed_triangle_set
         v = (frame * v.cast<double>()).cast<float>();
 
     const size_t         debug_mark = (debug != nullptr) ? debug->mark() : 0;
+    // The UV channel rides along untouched: a uv is a coordinate in the texture, not on the model, so
+    // the frame the mesh is measured in does not reach it.
     indexed_triangle_set out = build_texture_displacement_in_place(world, layers, facets_data, options,
-                                                                   progress, color, mirrored, debug, stats);
+                                                                   progress, color, mirrored, debug, stats, model_uv);
     // Everything the bake recorded is in world millimetres, like `out` itself. The debug view draws in
     // the volume's local frame, so the stages are brought back the same way the result is.
     if (debug != nullptr)
@@ -3312,7 +3262,8 @@ indexed_triangle_set build_texture_displacement(const ModelVolume &volume)
 
     return build_texture_displacement(volume.mesh().its, volume.texture_displacement_layers, facets_data,
                                       volume.texture_displacement_options, {}, nullptr,
-                                      texture_displacement_volume_to_world(volume));
+                                      texture_displacement_volume_to_world(volume), nullptr, nullptr,
+                                      volume.has_texture_uv() ? &volume.texture_uv : nullptr);
 }
 
 void smooth_mesh_vertices(indexed_triangle_set &mesh, const std::vector<uint8_t> &movable, float strength,
@@ -3376,16 +3327,18 @@ void smooth_mesh_vertices(indexed_triangle_set &mesh, const std::vector<uint8_t>
 namespace {
 // One decoded texture + placement per sampleable layer, in blend (slot) order. Held by shared_ptr so
 // the returned closure owns it for as long as the subdivider keeps calling back.
-// An unwrap turned into something a *point* sampler can use. LSCM has no formula from position to
-// uv - it is a per-triangle map - so a point is placed on the painted patch (the nearest patch
-// triangle, and its barycentric coordinates there) and the uv is interpolated from that triangle's own
-// per-corner uvs. Exact for a point on the base surface, which is where both samplers are queried: the
-// displacement samples refined positions before moving them, and the colour pass samples the foot
-// point on the painted pieces.
+// A per-triangle uv map turned into something a *point* sampler can use. Neither of the two maps that
+// are not a formula from position to uv - the LSCM unwrap and the model's own UV channel - can be
+// evaluated at an arbitrary point directly, so a point is placed on the painted patch (the nearest
+// patch triangle, and its barycentric coordinates there) and the uv is interpolated from that
+// triangle's own per-corner uvs. Exact for a point on the base surface, which is where both samplers
+// are queried: the displacement samples refined positions before moving them, and the colour pass
+// samples the foot point on the painted pieces.
 struct LscmLookup {
-    indexed_triangle_set    patch;  // the layer's painted patch, as the unwrap was solved on
+    indexed_triangle_set    patch;  // the layer's painted patch, as the uvs were computed on
     AABBTreeIndirect::Tree3f tree;
-    std::vector<Vec2f>      corner; // compute_lscm_corner_uvs(patch, layer)
+    // compute_lscm_corner_uvs(patch, layer), or compute_model_corner_uvs() for a ModelUV layer
+    std::vector<Vec2f>      corner;
 
     // False when `pos` is not on this layer's patch (farther than `tol`): there is no uv there, so the
     // layer contributes nothing - the same as a non-tiled texture outside its placement.
@@ -3398,15 +3351,9 @@ struct LscmLookup {
         if (d2 < 0.f || d2 > tol * tol || hit >= patch.indices.size())
             return false;
         const stl_triangle_vertex_indices &t = patch.indices[hit];
-        const Vec3f &a = patch.vertices[size_t(t[0])], &b = patch.vertices[size_t(t[1])], &c = patch.vertices[size_t(t[2])];
-        const Vec3f  e0 = b - a, e1 = c - a, ep = foot - a;
-        const float  d00 = e0.dot(e0), d01 = e0.dot(e1), d11 = e1.dot(e1), dp0 = ep.dot(e0), dp1 = ep.dot(e1);
-        const float  den = d00 * d11 - d01 * d01;
-        float        w1 = 1.f / 3.f, w2 = 1.f / 3.f; // a degenerate triangle takes its centroid's uv
-        if (std::abs(den) > 1e-20f) {
-            w1 = (d11 * dp0 - d01 * dp1) / den;
-            w2 = (d00 * dp1 - d01 * dp0) / den;
-        }
+        float w1 = 0.f, w2 = 0.f; // a degenerate triangle takes its centroid's uv
+        barycentric_weights(patch.vertices[size_t(t[0])], patch.vertices[size_t(t[1])], patch.vertices[size_t(t[2])],
+                            foot, w1, w2);
         const Vec2f *c3 = &corner[hit * 3];
         uv = (1.f - w1 - w2) * c3[0] + w1 * c3[1] + w2 * c3[2];
         return true;
@@ -3465,7 +3412,7 @@ struct PreparedLayer {
 // where a layer is placed. `need_color` additionally drops layers that cannot contribute colour.
 std::shared_ptr<std::vector<PreparedLayer>> prepare_sampleable_layers(
     const indexed_triangle_set &base_mesh, const std::vector<TextureDisplacementLayer> &layers,
-    const TextureDisplacementFacetsData &facets_data, bool need_color)
+    const TextureDisplacementFacetsData &facets_data, bool need_color, const std::vector<Vec2f> *model_uv)
 {
     auto prepared = std::make_shared<std::vector<PreparedLayer>>();
 
@@ -3496,9 +3443,14 @@ std::shared_ptr<std::vector<PreparedLayer>> prepare_sampleable_layers(
         if (tex.empty() || (need_color && !tex.has_color()))
             continue;
 
+        const bool model_uv_layer = layer->projection_method == TextureProjectionMethod::ModelUV &&
+                                    model_uv != nullptr && model_uv->size() == base_mesh.indices.size() * 3;
+
         TriangleSelector selector(selector_mesh);
         selector.deserialize(data, false);
-        const indexed_triangle_set patch = selector.get_facets_strict(EnforcerBlockerType::ENFORCER);
+        std::vector<int>           patch_source; // only the model's own channel needs it; see the classic path
+        const indexed_triangle_set patch =
+            selector.get_facets_strict(EnforcerBlockerType::ENFORCER, model_uv_layer ? &patch_source : nullptr);
         if (patch.indices.empty())
             continue;
 
@@ -3508,12 +3460,16 @@ std::shared_ptr<std::vector<PreparedLayer>> prepare_sampleable_layers(
         texture_displacement_patch_frame(patch, vertex_normals, centroid, axis, average_normal);
 
         std::shared_ptr<const LscmLookup> lscm;
-        if (layer->projection_method == TextureProjectionMethod::LSCM) {
+        if (model_uv_layer || layer->projection_method == TextureProjectionMethod::LSCM) {
             // Solved on the very patch the classic path and the GUI solve it on (same geometry, seam
             // angle and edges), so it hits the unwrap cache and lands exactly where the UV editor
-            // shows it, hand-placed islands and UV edits included.
+            // shows it, hand-placed islands and UV edits included. A ModelUV layer needs no solve at
+            // all - its corners are read straight out of the volume's channel - but it is looked up
+            // through the same per-triangle machinery, for the same reason: there is no formula from a
+            // point to its uv.
             auto l    = std::make_shared<LscmLookup>();
-            l->corner = compute_lscm_corner_uvs(patch, *layer);
+            l->corner = model_uv_layer ? compute_model_corner_uvs(base_mesh, *model_uv, patch, patch_source) :
+                                          compute_lscm_corner_uvs(patch, *layer);
             if (l->corner.size() == patch.indices.size() * 3) {
                 l->patch = patch;
                 l->tree  = AABBTreeIndirect::build_aabb_tree_over_indexed_triangle_set(l->patch.vertices, l->patch.indices);
@@ -3539,11 +3495,12 @@ ColorFieldSampler make_combined_color_sampler(const indexed_triangle_set
                                               const std::vector<TextureDisplacementLayer> &layers,
                                               const TextureDisplacementFacetsData         &facets_data,
                                               ColorQuantizeFn                              quantize,
-                                              ColorQuantizeFn                              quantize_pure)
+                                              ColorQuantizeFn                              quantize_pure,
+                                              const std::vector<Vec2f>                    *model_uv)
 {
     if (!quantize)
         return nullptr;
-    auto prepared = prepare_sampleable_layers(base_mesh, layers, facets_data, /* need_color */ true);
+    auto prepared = prepare_sampleable_layers(base_mesh, layers, facets_data, /* need_color */ true, model_uv);
     if (prepared->empty())
         return nullptr;
     // Per layer: a flat-colour image is matched against the filaments alone, when that quantizer
@@ -3574,9 +3531,10 @@ ColorFieldSampler make_combined_color_sampler(const indexed_triangle_set
 
 HeightFieldSampler make_combined_displacement_sampler(const indexed_triangle_set                  &base_mesh,
                                                       const std::vector<TextureDisplacementLayer> &layers,
-                                                      const TextureDisplacementFacetsData         &facets_data)
+                                                      const TextureDisplacementFacetsData         &facets_data,
+                                                      const std::vector<Vec2f>                    *model_uv)
 {
-    auto prepared = prepare_sampleable_layers(base_mesh, layers, facets_data, /* need_color */ false);
+    auto prepared = prepare_sampleable_layers(base_mesh, layers, facets_data, /* need_color */ false, model_uv);
     if (prepared->empty())
         return nullptr;
 

src/libslic3r/TextureDisplacement.hpp

@@ -86,6 +86,17 @@ enum class TextureProjectionMethod : int
     // that is inherent to view projection and is the user's call, not a bug. The projector's two
     // in-plane axes live in TextureDisplacementLayer::view_project_right/up.
     ViewProjected = 4,
+    // The model's own texture coordinates, as the file it was imported from carried them (see
+    // ModelVolume::texture_uv). Nothing is unwrapped or projected: the artist's layout *is* the
+    // placement, so a texture authored against that layout - the model's own albedo map, say - lands
+    // exactly where it was painted. Automatically picked for a new layer on a volume that has a UV
+    // channel, since re-unwrapping a model that already carries one can only be worse than using it.
+    //
+    // The uv is already normalized, so unlike every method above it is not measured in millimetres:
+    // "Tile size" and the non-square aspect correction do not apply to it (the layer's rotation and
+    // offset still do). Falls back to Triplanar when the volume has no channel, exactly as LSCM falls
+    // back when a patch cannot be flattened.
+    ModelUV       = 5,
 };
 
 // Dihedral angle (degrees) above which an edge between two painted triangles becomes a chart seam
@@ -121,6 +132,11 @@ enum class TextureBlendMode : int
     Subtract = 1, // acc - value          (carve this layer's relief out of the layers below)
     Multiply = 2, // acc * (value / 1mm)  (mask/modulate the layers below by this layer)
     Divide   = 3, // acc / (value / 1mm)  (inverse mask; guarded against a zero/near-zero divisor)
+    // acc = value: this layer replaces what is under it instead of combining with it, so where it is
+    // painted only its own relief remains. The image editor's "Normal" mode, under the name the panel
+    // uses. Note the stack's *colour* already behaves this way - a higher slot's colour overwrites a
+    // lower one's where they overlap - so this is what makes the displacement agree with it.
+    Override = 4,
 };
 
 // Combines one layer's signed displacement `value` (mm) into `accumulated` (mm) per `mode`.
@@ -154,38 +170,6 @@ struct TextureIsland
 // chart to its true mm area, so a freshly unwrapped patch has uniform texel density to begin with.
 void average_island_scales(std::vector<TextureIsland> &islands);
 
-// Photo-style adjustments to a layer's source image, as the gizmo's image-adjustment panel sets them.
-//
-// These are *not* layer parameters: nothing here is stored on TextureDisplacementLayer and nothing here is
-// re-applied at bake time. The panel applies them once, to the image, and the result becomes the layer's
-// image - so the adjusted pixels feed the colour and the displacement together, and a brightness change
-// really does change the relief. That is the intended behaviour: one image, one source of truth, rather
-// than a second set of knobs the bake would have to replay in the right order.
-//
-// Contrast with TextureDisplacementLayer::smoothing, which *is* a layer parameter applied on every decode:
-// `blur` here is a destructive edit of the image, `smoothing` is a live low-pass over whatever the image is.
-struct TextureAdjustments
-{
-    float brightness = 0.f; // [-1, 1]; 0 unchanged, -1 black, +1 white
-    float contrast   = 0.f; // [-1, 1]; 0 unchanged, -1 flat mid-grey, +1 hard threshold
-    float sharpness  = 0.f; // [0, 1];  0 unchanged. Unsharp-mask amount
-    float blur       = 0.f; // [0, 1];  0 unchanged. Fraction of SOURCE_BLUR_SPAN, as `smoothing` is
-    float hue_deg    = 0.f; // [-180, 180]; 0 unchanged. No effect on a grayscale image - grey has no hue
-
-    bool identity() const
-    {
-        return brightness == 0.f && contrast == 0.f && sharpness == 0.f && blur == 0.f && hue_deg == 0.f;
-    }
-    // Exact equality, which is what is wanted: these come straight off sliders, and the question asked of
-    // them is "is this still the value the preview on screen was computed from", not "are these close".
-    bool operator==(const TextureAdjustments &o) const
-    {
-        return brightness == o.brightness && contrast == o.contrast && sharpness == o.sharpness &&
-               blur == o.blur && hue_deg == o.hue_deg;
-    }
-    bool operator!=(const TextureAdjustments &o) const { return !(*this == o); }
-};
-
 // One texture asset plus its projection/displacement parameters. Several layers may be painted
 // onto overlapping areas of the same volume: their displacements are combined per vertex, in slot
 // order, each layer folding into the total via its own TextureBlendMode (see
@@ -325,18 +309,6 @@ struct TextureDisplacementLayer
     // for the boundary to be drawn on.
     bool color_enabled = false;
 
-    // Live, unsaved image adjustments from the gizmo's image-adjustment panel, applied by
-    // decode_height_texture() on top of the decoded image - so while the panel is open the relief, the
-    // colour, the thumbnails and the bake all see the adjusted image, and moving a slider really does
-    // change the displacement. See TextureAdjustments.
-    //
-    // Deliberately *not* serialized, by either save()/load() here or the .3mf: it is the state of an open
-    // editor, not a property of the layer. The panel resets it when it closes, and "Save as copy" resolves
-    // it by writing a new image and pointing the layer at that - which is the only way an adjustment
-    // becomes permanent. A project saved mid-adjustment therefore stores the unadjusted image, which is
-    // the honest answer: nothing was committed.
-    TextureAdjustments preview_adjust;
-
     bool empty() const { return !image_data || image_data->empty(); }
 
     template<class Archive> void save(Archive &ar) const
@@ -533,36 +505,6 @@ DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer
 // texture - cheap enough to ask every frame. Smoothing does not change it, so the raw decode is what is read.
 bool height_texture_has_color(const TextureDisplacementLayer &layer);
 
-// Applies `adj` to `src` and returns the result; `src` is left alone. An empty `src`, or an identity
-// `adj`, gives back a copy.
-//
-// Order is tonal, then spatial: brightness, contrast and hue per texel first, then blur, then sharpness.
-// Sharpness last is what lets the two spatial knobs be used together - blur to kill speckle, then
-// sharpness to put the real edges back - instead of the blur simply undoing the sharpen.
-//
-// Grayscale in, grayscale out (`rgb` stays empty): promoting a grey image to RGB would hand the layer's
-// colour feature a row of identical greys to "colour" the model with, and triple the stored PNG for it.
-// For a colour image the height is recomputed as the luminance of the *adjusted* colour, with
-// decode_height_texture()'s own coefficients, so the relief and the colour can never drift apart.
-DecodedHeightTexture apply_texture_adjustments(const DecodedHeightTexture &src, const TextureAdjustments &adj);
-
-// Blur radius, in texels, that TextureAdjustments::blur == 1 means on a `min(width, height)`-sized image:
-// the same 5%-of-the-short-side span the Smoothing slider uses, under the same 48-texel cost cap, so the
-// two controls bite at the same rate and a user moving between them is not surprised.
-float adjustment_blur_radius(float blur, int width, int height);
-
-// Box-filters `src` down so neither side exceeds `max_px`, preserving aspect; never upscales, and
-// returns a copy when it already fits. Colour and height are filtered the same way, and the height
-// stays the height - it is not recomputed from the filtered colour, because a box filter is linear and
-// luminance is linear in the channels, so the two agree already.
-//
-// This is what lets the adjustment panel's live preview cost depend on the size of the box it is drawn
-// in rather than on the size of the image: adjusting a downscaled copy per slider frame, and the
-// full-size image only once, on commit. A box filter (rather than a plain decimation) is the point -
-// these textures are high-frequency by nature, and dropping texels would alias the preview into
-// showing detail the adjustment is not actually producing.
-DecodedHeightTexture downscale_height_texture(const DecodedHeightTexture &src, int max_px);
-
 // Maps a linear RGB colour in [0, 1] to an index into the caller's palette, or -1 for "no colour".
 //
 // Deliberately a callback rather than a function here: matching a colour to a filament is a
@@ -615,7 +557,13 @@ Vec2f project_planar(const Vec3f &position, const Vec3f &normal);
 // squeezed into a square tile: `tiling_scale` is the tile's size along u, and the tile is
 // `tiling_scale * height / width` mm along v, which keeps texels square. 1 (the default) is the
 // square case and leaves the coordinate exactly as it always was.
-Vec2f apply_uv_transform(const Vec2f &planar, const TextureDisplacementLayer &layer, float aspect = 1.f);
+//
+// `normalized_uv` says the coordinate is already a uv rather than a millimetre measurement on the
+// model - which is what TextureProjectionMethod::ModelUV hands in. Then neither the tiling scale (mm
+// per tile is meaningless for it) nor the aspect correction (the artist's layout already accounts for
+// the image's proportions) applies, and only the rotation and offset are left.
+Vec2f apply_uv_transform(const Vec2f &planar, const TextureDisplacementLayer &layer, float aspect = 1.f,
+                         bool normalized_uv = false);
 
 // Applies a row-major 3x4 projective matrix (see TextureDisplacementLayer::view_project_matrix) to a
 // local-space point, writing the resulting texture uv. Returns false - and leaves `uv` untouched -
@@ -765,6 +713,80 @@ std::vector<Vec2f> compute_lscm_uvs(const indexed_triangle_set &patch, const Tex
 // Returns an empty vector if the patch has no triangles or the unwrap carries no source_face map.
 std::vector<Vec2f> compute_lscm_corner_uvs(const indexed_triangle_set &patch, const TextureDisplacementLayer &layer);
 
+// Three UVs per patch triangle, read out of the model's *own* UV channel - the
+// TextureProjectionMethod::ModelUV counterpart of compute_lscm_corner_uvs(), and laid out the same way
+// (corner k of triangle i at index 3i+k).
+//
+// `model_uv` is the volume's channel: three uvs per triangle of `base_mesh`, in its triangle order
+// (see ModelVolume::texture_uv). `patch_source` maps each patch triangle back to the base-mesh
+// triangle it was cut from - TriangleSelector::get_facets_strict()'s out_source. A patch triangle is
+// always a piece of exactly one base triangle, so each of its corners is interpolated barycentrically
+// inside that triangle's three uvs. That is what keeps a sub-triangle the brush split (whose corners
+// are not base-mesh vertices at all) on the texture, and what keeps the two sides of a UV seam
+// reading from their own island instead of from one averaged coordinate.
+//
+// Returns an empty vector when the channel does not match `base_mesh`, when `patch_source` does not
+// match `patch`, or when either is empty - the callers treat that as "no placement" and fall back,
+// exactly as they do for an unwrap that failed.
+std::vector<Vec2f> compute_model_corner_uvs(const indexed_triangle_set &base_mesh,
+                                            const std::vector<Vec2f>   &model_uv,
+                                            const indexed_triangle_set &patch,
+                                            const std::vector<int>     &patch_source);
+
+// One UV per patch vertex, collapsed from a per-corner array: the first corner to reach a vertex wins.
+// This is the per-corner/per-vertex split compute_lscm_uvs() documents, applied to any corner array -
+// displacement is per-vertex, so a vertex on a seam has to settle on one of its copies.
+// Returns an empty vector if `corner` is not three per patch triangle.
+std::vector<Vec2f> collapse_corner_uvs(const indexed_triangle_set &patch, const std::vector<Vec2f> &corner);
+
+// Resamples a per-corner UV channel from `src_mesh` onto `dst_mesh`, for when something replaces a
+// volume's mesh and the model's own UV channel has to come along: the colour import's painted mesh,
+// the gizmo's remesh/subdivide, the default bake pipeline's rebuild. Each destination corner takes the
+// uv of its closest point on the source surface, interpolated barycentrically inside the source
+// triangle it lands on - the same transfer LscmLookup does per point, run over every corner.
+//
+// Exact wherever the two meshes describe the same surface, which is the case for every caller here
+// (they subdivide, repair or displace it, they do not reshape it). A corner that lands nowhere near
+// the source - farther than `max_distance` (negative: no limit) - takes (0, 0).
+//
+// One thing a positional transfer cannot reproduce: a *seam* vertex, where one position carries a
+// different uv in each island that meets there. Position alone does not say which island a corner
+// belongs to, so corners on a seam all take whichever island the nearest-triangle lookup lands on,
+// and the texture can be off by up to one triangle in a band along the island borders. Doing better
+// needs a triangle-to-triangle correspondence, which only some of the stages that replace a mesh
+// have (a remesh has none at all).
+//
+// Returns an empty vector when `src_uv` is not three per source triangle, or when either mesh is empty.
+std::vector<Vec2f> transfer_uv_channel(const indexed_triangle_set &src_mesh,
+                                       const std::vector<Vec2f>   &src_uv,
+                                       const indexed_triangle_set &dst_mesh,
+                                       float                       max_distance = -1.f);
+
+// Carries a per-facet paint annotation - the colour paint above all - from a mesh onto the mesh a
+// bake produced from it: every triangle of `dst_mesh` takes the state painted at its own foot point on
+// `src_mesh`, i.e. on the nearest point of the surface it was built from. Returned as one
+// EnforcerBlockerType per `dst_mesh` triangle, 0 (NONE) where that foot point carried no paint.
+//
+// ModelVolume::restore_painting() cannot do this. Its remap pairs a source paint triangle with a
+// target triangle that *overlaps* it to within 0.01 mm, which is right for a remesh or a
+// simplification - they leave the surface where it was - and useless after a bake, which moves the
+// surface by the relief depth. Measured on a model displaced by a tenth of its own size, that remap
+// kept a quarter of the colour and left the rest unpainted; this keeps essentially all of it, because
+// a foot point is exactly as far away as the relief is deep and the lookup does not care how far that
+// is.
+//
+// The source's *sub*-triangles are what is looked up, not its triangles, so the part of a triangle a
+// brush stroke only clipped a corner off keeps its own state rather than rounding to the whole
+// triangle's. No distance limit is needed or wanted: the nearest point on the source surface is where
+// a baked triangle came from however far the relief carried it, and an unpainted origin reports NONE
+// on its own.
+//
+// Returns an empty vector when `src_paint` is empty or either mesh is - the caller then has nothing to
+// carry, which is not the same as "carry nothing".
+std::vector<uint8_t> transfer_facet_paint(const indexed_triangle_set                    &src_mesh,
+                                         const TriangleSelector::TriangleSplittingData &src_paint,
+                                         const indexed_triangle_set                    &dst_mesh);
+
 // The TextureDisplacementLayer::lscm_uv_overrides key for one unwrapped vertex (an index into PatchUnwrap::uvs).
 inline int lscm_uv_override_key(int unwrapped_vertex) { return -(unwrapped_vertex + 1); }
 
@@ -823,6 +845,10 @@ using TextureDisplacementFacetsData = std::array<TriangleSelector::TriangleSplit
 //
 // `color`, when given, also reports which filament each triangle should print in - see
 // TextureColorRequest.
+//
+// `model_uv`, when given, is the volume's own UV channel (three uvs per base-mesh triangle, see
+// ModelVolume::texture_uv) and is what a TextureProjectionMethod::ModelUV layer maps through. A layer
+// set to ModelUV without it falls back to Triplanar.
 struct TextureColorRequest
 {
     // RGB -> palette index. Supplied by the GUI, which owns both the perceptual matching and the list
@@ -897,7 +923,9 @@ indexed_triangle_set build_texture_displacement(const indexed_triangle_set
                                                  // stage, already brought back into `base_mesh`'s frame.
                                                  BakeStageRecorder                           *debug = nullptr,
                                                  // When given, receives what the bake spent.
-                                                 TextureBakeStats                            *stats = nullptr);
+                                                 TextureBakeStats                            *stats = nullptr,
+                                                 // The model's own UV channel; see above.
+                                                 const std::vector<Vec2f>                    *model_uv = nullptr);
 
 // `volume`'s mesh coordinates -> world millimetres: its first instance's transform times its own.
 // The mesh is shared by every instance, so a multi-instance object can only be baked for one of
@@ -972,11 +1000,15 @@ ColorFieldSampler make_combined_color_sampler(const indexed_triangle_set
                                               const std::vector<TextureDisplacementLayer> &layers,
                                               const TextureDisplacementFacetsData         &facets_data,
                                               ColorQuantizeFn                              quantize,
-                                              ColorQuantizeFn                              quantize_pure = nullptr);
+                                              ColorQuantizeFn                              quantize_pure = nullptr,
+                                              // The model's own UV channel, for ModelUV layers; see
+                                              // build_texture_displacement().
+                                              const std::vector<Vec2f>                    *model_uv = nullptr);
 
 HeightFieldSampler make_combined_displacement_sampler(const indexed_triangle_set                  &base_mesh,
                                                       const std::vector<TextureDisplacementLayer> &layers,
-                                                      const TextureDisplacementFacetsData         &facets_data);
+                                                      const TextureDisplacementFacetsData         &facets_data,
+                                                      const std::vector<Vec2f>                    *model_uv = nullptr);
 
 // Uniformly subdivides `mesh` (every triangle recursively split into 4 via edge midpoints, using a
 // shared cache so a midpoint is computed once and reused by both triangles on either side of that
@@ -1181,6 +1213,10 @@ struct TextureDisplacementPrepareResult
 {
     indexed_triangle_set          mesh;
     TextureDisplacementFacetsData masks;
+    // The model's own UV channel, resampled onto `mesh` (see transfer_uv_channel()). Empty when the
+    // volume had none. Like the masks it is handed back rather than left to the caller to recompute,
+    // because only the run itself knows which stages replaced the mesh.
+    std::vector<Vec2f>            uv;
     // The remesh landed but no layer's paint survived being carried onto it. Nothing is committed:
     // everything downstream is driven by that paint, so baking on would bake a flat mesh.
     bool                          paint_lost = false;

src/libslic3r/TexturePainting.cpp

@@ -25,6 +25,7 @@
 #include "TextureToColor/ColorUtils.hpp"
 
 #include "Model.hpp"
+#include "TextureDisplacement.hpp"
 #include "TextureToColor/TriMesh.hpp"
 #include "TriangleMesh.hpp"
 #include "TriangleSelector.hpp"
@@ -554,9 +555,29 @@ bool apply_painted_mesh_to_volume(
                 << ", unit_scale=" << unit_scale << ")";
     }
 
+    // The model's own UV channel is indexed by triangle, and this replaces the triangles, so it has
+    // to be resampled onto them. Kept rather than dropped because it is the layout the model was
+    // authored against: a texture-displacement layer set to ModelUV maps through it, and the colour
+    // import is exactly the path a model that carries one arrives by.
+    const indexed_triangle_set old_its = volume.has_texture_uv() ? volume.mesh().its : indexed_triangle_set{};
+    const std::vector<Vec2f>   old_uv  = volume.texture_uv;
+
     volume.set_mesh(std::move(new_mesh));
     volume.calculate_convex_hull();
 
+    // Resampled here and not further down, while the two meshes still share a frame: the painted mesh
+    // was just shifted by the same source.mesh_offset the old one was centred by, so the only thing
+    // between them is whatever drift the repair introduced. The re-centering below translates the mesh
+    // again, and a translation is exactly what a closest-point transfer cannot see through - it would
+    // read every uv off a point that far away. A uv is a coordinate in the texture, so it does not care
+    // about either shift; it just has to be read before the second one happens.
+    if (!old_its.indices.empty())
+        volume.texture_uv = transfer_uv_channel(old_its, old_uv, volume.mesh().its);
+    else
+        // No channel to carry, so make sure none is left behind either: a leftover of the right length
+        // would read as a valid channel against a mesh it was never measured on.
+        volume.reset_texture_uv();
+
     // Re-center the replaced mesh so its bbox center sits at the origin,
     // matching what center_geometry_after_creation did for the original mesh.
     // CGAL repair / subdivision may shift the bbox center (drift); without

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.cpp

@@ -43,7 +43,6 @@
 #include <cstdint>
 #include <functional>
 #include <chrono>
-#include <future>
 #include <cstdio>
 #include <glad/gl.h>
 #include <imgui.h>
@@ -121,14 +120,6 @@ constexpr int THUMBNAIL_MAX_PX = 128;
 // blur of it - which is what made Fast look flatter and softer than the result it was previewing.
 constexpr int HEIGHT_TEX_MAX_PX = 2048;
 
-// Size the image-adjustment panel's live preview is computed and uploaded at. The panel draws the image
-// in a box about 240 px wide, so there is nothing to show above this - and the preview is recomputed on
-// every slider move, which is what makes its cost worth bounding. Measured on a 1024x1024 with every
-// knob engaged, a full-size pass is 13-19 ms grayscale / 40-60 ms in colour (130-190 ms at 2048 in
-// colour); the same pass on a 384 px copy is 3-4 ms / 9-12 ms, and it runs off the UI thread besides.
-// The full-size image is only ever adjusted once, on commit.
-constexpr int ADJUST_PREVIEW_MAX_PX = 384;
-
 // How many rings of vertex-adjacent triangles either side of the paint's edge join the border refine
 // band (see collect_paint_region()). Two is enough to grade the size change without the band's own
 // cost growing to matter: it is a ring around a perimeter, not an area.
@@ -534,10 +525,6 @@ void GLGizmoTextureDisplacement::on_shutdown()
     // progress poll, and its completion handler then finds nothing to do.
     m_preview_generation->fetch_add(1);
     m_preview_job_pending = false;
-    // The adjustment panel holds a full-size decode of its layer's image, which is the largest thing
-    // here; a closed gizmo should not keep it alive. Discards the edit, as closing the gizmo on an open
-    // panel implies.
-    close_image_adjust();
     // The palette caches hold the last volume's images; a closed gizmo should not keep them alive.
     m_palette_cache.clear();
     m_palette_quantizer      = nullptr;
@@ -1234,9 +1221,33 @@ indexed_triangle_set GLGizmoTextureDisplacement::patch_in_world(const indexed_tr
     return world;
 }
 
-std::vector<Vec2f> GLGizmoTextureDisplacement::compute_layer_vertex_uvs(const indexed_triangle_set     &local_patch,
-                                                                       const TextureDisplacementLayer &layer) const
+std::vector<Vec2f> GLGizmoTextureDisplacement::model_uv_corners(const indexed_triangle_set     &local_patch,
+                                                                const TextureDisplacementLayer &layer,
+                                                                const std::vector<int>         *patch_source) const
 {
+    const ModelVolume *mv = texture_volume();
+    if (layer.projection_method != TextureProjectionMethod::ModelUV || patch_source == nullptr || mv == nullptr ||
+        !mv->has_texture_uv())
+        return {};
+    // The channel is indexed against the volume's *local* mesh, and a uv is a coordinate in the
+    // texture rather than on the model, so unlike every projected method this never goes through
+    // patch_in_world() - there is no millimetre measurement here for a world scale to change.
+    std::vector<Vec2f> uv = compute_model_corner_uvs(mv->mesh().its, mv->texture_uv, local_patch, *patch_source);
+    for (Vec2f &p : uv)
+        // Already a uv: no tiling scale, no aspect correction - see apply_uv_transform().
+        p = apply_uv_transform(p, layer, 1.f, /* normalized_uv */ true);
+    return uv;
+}
+
+std::vector<Vec2f> GLGizmoTextureDisplacement::compute_layer_vertex_uvs(const indexed_triangle_set     &local_patch,
+                                                                       const TextureDisplacementLayer &layer,
+                                                                       const std::vector<int>         *patch_source) const
+{
+    if (layer.projection_method == TextureProjectionMethod::ModelUV)
+        // Collapsed to one per vertex the same way the unwrap is - a vertex has one position, so the
+        // displacement can only read one height for it.
+        return collapse_corner_uvs(local_patch, model_uv_corners(local_patch, layer, patch_source));
+
     // The bake maps the texture in world millimetres, so "Tile size (mm)" means the same thing on a
     // scaled instance as it does on an untouched one (see build_texture_displacement()). Everything
     // that has to agree with the bake - the fast preview's uvs, the checker/distortion overlays -
@@ -1296,8 +1307,11 @@ int GLGizmoTextureDisplacement::layer_projection_frame(const indexed_triangle_se
 }
 
 std::vector<Vec2f> GLGizmoTextureDisplacement::compute_layer_corner_uvs(const indexed_triangle_set     &local_patch,
-                                                                        const TextureDisplacementLayer &layer) const
+                                                                        const TextureDisplacementLayer &layer,
+                                                                        const std::vector<int>         *patch_source) const
 {
+    if (layer.projection_method == TextureProjectionMethod::ModelUV)
+        return model_uv_corners(local_patch, layer, patch_source);
     if (layer.projection_method == TextureProjectionMethod::LSCM) {
         const indexed_triangle_set patch  = patch_in_world(local_patch);
         const float                aspect = layer_texture_aspect(layer);
@@ -1307,7 +1321,7 @@ std::vector<Vec2f> GLGizmoTextureDisplacement::compute_layer_corner_uvs(const in
         return uv;
     }
     // Single-valued per point: fan the per-vertex result out over the corners.
-    const std::vector<Vec2f> per_vertex = compute_layer_vertex_uvs(local_patch, layer);
+    const std::vector<Vec2f> per_vertex = compute_layer_vertex_uvs(local_patch, layer, patch_source);
     if (per_vertex.size() != local_patch.vertices.size())
         return {};
     std::vector<Vec2f> corner(local_patch.indices.size() * 3);
@@ -1328,7 +1342,11 @@ void GLGizmoTextureDisplacement::rebuild_shaded_preview_mesh()
     // Uses the *live* selector (not the flushed model facet data), so this reflects an in-progress
     // stroke immediately rather than only once it ends - the point of this preview mode is to be
     // the fast, no-CPU-meshing one.
-    const indexed_triangle_set patch = m_triangle_selectors[0]->get_facets_strict(EnforcerBlockerType::ENFORCER);
+    // The source map comes along because a ModelUV layer's uvs are read per base-mesh triangle; every
+    // other mapping ignores it.
+    std::vector<int>           patch_source;
+    const indexed_triangle_set patch =
+        m_triangle_selectors[0]->get_facets_strict(EnforcerBlockerType::ENFORCER, &patch_source);
     if (patch.indices.empty())
         return;
 
@@ -1352,7 +1370,8 @@ void GLGizmoTextureDisplacement::rebuild_shaded_preview_mesh()
     // Per *corner*, not per vertex: the mesh below is flat (unshared) anyway, so each triangle can
     // carry its own chart's UVs - see compute_layer_corner_uvs().
     const TextureDisplacementLayer *active = active_layer();
-    std::vector<Vec2f> corner_uv = active != nullptr ? compute_layer_corner_uvs(patch, *active) : std::vector<Vec2f>{};
+    std::vector<Vec2f> corner_uv = active != nullptr ? compute_layer_corner_uvs(patch, *active, &patch_source) :
+                                                       std::vector<Vec2f>{};
     m_shaded_preview_uses_vertex_uv = corner_uv.size() == patch.indices.size() * 3;
     if (!m_shaded_preview_uses_vertex_uv)
         corner_uv.clear();
@@ -2009,7 +2028,9 @@ void GLGizmoTextureDisplacement::rebuild_uvcheck_mesh()
     const ModelVolume *mv = texture_volume();
     if (mv == nullptr || m_triangle_selectors.empty())
         return;
-    const indexed_triangle_set patch = m_triangle_selectors[0]->get_facets_strict(EnforcerBlockerType::ENFORCER);
+    std::vector<int>           patch_source; // only ModelUV reads it; see compute_layer_vertex_uvs()
+    const indexed_triangle_set patch =
+        m_triangle_selectors[0]->get_facets_strict(EnforcerBlockerType::ENFORCER, &patch_source);
     if (patch.indices.empty())
         return;
     // Everything below works in the *patch's* vertex space, not the mesh's. Those agree only until a
@@ -2023,7 +2044,7 @@ void GLGizmoTextureDisplacement::rebuild_uvcheck_mesh()
 
     // The checker samples wherever the projection puts it; the projections the shader can't
     // reconstruct (LSCM, ViewProjected) get a precomputed per-vertex uv, the rest project in-shader.
-    std::vector<Vec2f> uv       = compute_layer_vertex_uvs(patch, *layer);
+    std::vector<Vec2f> uv       = compute_layer_vertex_uvs(patch, *layer, &patch_source);
     const bool         have_uvs = uv.size() == patch.vertices.size();
     m_uvcheck_uses_vertex_uv    = have_uvs;
     m_uvcheck_projection_mode   = have_uvs ? 0 :
@@ -2032,7 +2053,7 @@ void GLGizmoTextureDisplacement::rebuild_uvcheck_mesh()
     // different uv in each island it borders, so the shared-vertex form drew one triangle per face from
     // a neighbouring island's placement. Only the *drawing* needs this; the distortion metric below is
     // a per-vertex average by construction and keeps using `uv`.
-    const std::vector<Vec2f> corner_uv = compute_layer_corner_uvs(patch, *layer);
+    const std::vector<Vec2f> corner_uv = compute_layer_corner_uvs(patch, *layer, &patch_source);
     const bool               have_corner_uvs = have_uvs && corner_uv.size() == patch.indices.size() * 3;
 
     // Per-vertex area distortion in [0,1] (0.5 == ideal), only when both requested and possible.
@@ -2308,6 +2329,8 @@ void GLGizmoTextureDisplacement::queue_preview_job()
     if (input.options.pipeline_v2)
         input.options.v2_max_triangles_k = 0;
     input.volume_to_world = texture_displacement_volume_to_world(*mv);
+    if (mv->has_texture_uv())
+        input.model_uv = mv->texture_uv;
     for (int i = 0; i < int(TEXTURE_DISPLACEMENT_MAX_LAYERS); ++i)
         input.facets_data[size_t(i)] = mv->texture_displacement_facet(i).get_data();
     // Captured here rather than read in the handler: the palette is main-thread state, and the preview
@@ -2463,12 +2486,9 @@ void GLGizmoTextureDisplacement::update_uv_editor()
     // before, and independently of, the unwrap - the texture belongs on screen before anything is unwrapped - and
     // only when the choice, the layer's image or its smoothing changed, because the height image is large.
     const UVBackground desired_bg = (m_uv_check_mode == UVCheckMode::Checker) ? UVBackground::Checker : UVBackground::Height;
-    const bool bg_smoothing_changed = (desired_bg == UVBackground::Height) &&
-                                      (m_uv_editor_bg_smoothing != layer->smoothing ||
-                                       !(m_uv_editor_bg_adjust == layer->preview_adjust));
+    const bool bg_smoothing_changed = (desired_bg == UVBackground::Height) && (m_uv_editor_bg_smoothing != layer->smoothing);
     if (desired_bg != m_uv_editor_bg || layer->image_data.get() != m_uv_editor_bg_image || bg_smoothing_changed) {
         m_uv_editor_bg_smoothing = layer->smoothing;
-        m_uv_editor_bg_adjust    = layer->preview_adjust;
         m_uv_editor_bg_image     = layer->image_data.get();
         m_uv_editor_bg           = desired_bg;
         if (desired_bg == UVBackground::Checker) {
@@ -3692,9 +3712,10 @@ void GLGizmoTextureDisplacement::ensure_panel_icons()
         // Paint / Erase, brush cursor shape, mapping, tiling, placement and the dock toggle.
         "texture_displacement_add.svg", "texture_displacement_add_negative.svg", "circle_paint.svg",
         "menu_obj_sphere.svg", "menu_obj_cube.svg", "menu_obj_cylinder.svg", "texture_displacement_map_unwrap.svg",
-        "texture_displacement_map_view.svg", "texture_displacement_tile_repeat.svg", "menu_mirror_x.svg",
+        "texture_displacement_map_view.svg", "texture_displacement_map_model_uv.svg",
+        "texture_displacement_tile_repeat.svg", "menu_mirror_x.svg",
         "texture_displacement_adjust.svg", "canvas_drag.svg", "texture_displacement_move_up.svg",
-        "texture_displacement_move_down.svg", "texture_displacement_drag.svg", "cog.svg",
+        "texture_displacement_move_down.svg", "texture_displacement_drag.svg",
         "texture_displacement_select_all.svg", "texture_displacement_erase_all.svg",
     };
     std::vector<std::string> paths;
@@ -3739,6 +3760,11 @@ void GLGizmoTextureDisplacement::add_texture_layer()
 
     TextureDisplacementLayer layer;
     layer.slot = free_slot;
+    // A model that came with a UV channel is mapped by it. Re-unwrapping such a model throws away the
+    // layout it was authored against and can only be worse than using it, so the default follows the
+    // model rather than the other way round; the Mapping row still offers every other method.
+    if (mv->has_texture_uv())
+        layer.projection_method = TextureProjectionMethod::ModelUV;
     // Start the layer off on the first library texture rather than on nothing at all: a textureless
     // layer looks broken (painting on it appears to do nothing, because there is no height map to
     // displace by). The user swaps it for another from the layer's own picker.
@@ -3998,321 +4024,6 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
         m_picker_open_request = true;
     }
 }
-bool GLGizmoTextureDisplacement::load_image_adjust_source(const TextureDisplacementLayer &layer)
-{
-    if (layer.empty())
-        return false;
-
-    // The *raw* image: neither the layer's Smoothing nor the panel's own preview_adjust, so what the
-    // sliders act on is always the image as it is actually stored rather than the last preview of it.
-    // Without clearing preview_adjust here the adjustment would compound on itself every reload.
-    TextureDisplacementLayer raw = layer;
-    raw.smoothing                = 0.f;
-    raw.preview_adjust           = TextureAdjustments{};
-
-    DecodedHeightTexture decoded = decode_height_texture(raw);
-    if (decoded.empty())
-        return false;
-
-    m_adjust_source         = std::move(decoded);
-    m_adjust_preview_source = downscale_height_texture(m_adjust_source, ADJUST_PREVIEW_MAX_PX);
-    m_adjust_source_image   = layer.image_data.get();
-    // The unadjusted image, so the box is filled now rather than one background pass later. Pairing it
-    // with an identity `shown` is what makes update_image_adjust_preview() relaunch for the sliders'
-    // current values against the new source instead of deciding it is already showing them.
-    m_adjust_preview_shown = TextureAdjustments{};
-    m_adjust_preview_tex   = upload_height_thumbnail(m_adjust_preview_source, ADJUST_PREVIEW_MAX_PX);
-    m_adjust_preview_valid = m_adjust_preview_tex != nullptr;
-    return true;
-}
-
-void GLGizmoTextureDisplacement::open_image_adjust(const TextureDisplacementLayer &layer)
-{
-    if (layer.empty() || layer.slot < 0)
-        return;
-
-    close_image_adjust(); // reverts and clears any previous panel
-
-    if (!load_image_adjust_source(layer))
-        return;
-
-    m_adjust           = TextureAdjustments{};
-    m_adjust_applied   = TextureAdjustments{};
-    m_adjust_slot      = layer.slot;
-    const ModelVolume *mv = texture_volume();
-    m_adjust_volume_id = mv != nullptr ? mv->id().id : 0;
-}
-
-void GLGizmoTextureDisplacement::close_image_adjust()
-{
-    // Revert the layer's live adjustment. Every exit that reaches here is a discard: a commit resets
-    // preview_adjust itself, before pointing the layer at the file that already carries the edit, so this
-    // cannot undo a committed adjustment.
-    //
-    // Found by the id recorded when the panel opened rather than through texture_volume(), which answers
-    // for the *current* selection. One of the ways to get here is the selection having moved on, and
-    // reverting the newly selected object's layer instead would both miss the adjustment that is still
-    // live on the original volume and clear one the user never touched.
-    bool reverted = false;
-    if (m_adjust_slot >= 0 && m_adjust_volume_id != 0)
-        for (ModelObject *mo : wxGetApp().model().objects) {
-            for (ModelVolume *mv : mo->volumes) {
-                if (mv->id().id != m_adjust_volume_id)
-                    continue;
-                for (TextureDisplacementLayer &l : mv->texture_displacement_layers)
-                    if (l.slot == m_adjust_slot && !l.preview_adjust.identity()) {
-                        l.preview_adjust = TextureAdjustments{};
-                        reverted         = true;
-                    }
-            }
-        }
-
-    // std::async's future blocks here until the pass finishes. That is a few milliseconds on an image
-    // this small, and the alternative - a detached thread writing into the members of a closed panel -
-    // is worse.
-    if (m_adjust_preview_job.valid())
-        m_adjust_preview_job.wait();
-    m_adjust_preview_job = {};
-
-    m_adjust_slot           = -1;
-    m_adjust                = TextureAdjustments{};
-    m_adjust_applied        = TextureAdjustments{};
-    m_adjust_source         = DecodedHeightTexture{};
-    m_adjust_preview_source = DecodedHeightTexture{};
-    m_adjust_source_image   = nullptr;
-    m_adjust_volume_id      = 0;
-    m_adjust_preview_tex.reset();
-    m_adjust_preview_valid = false;
-
-    // Only while the gizmo is up: on_shutdown() also comes through here, and rebuilding a preview for a
-    // gizmo that is closing would be work for a model nobody is looking at. The reverted layer data is
-    // what matters there, and that is already done above.
-    if (reverted && m_state == On) {
-        rebuild_preview();
-        m_parent.set_as_dirty();
-    }
-}
-
-void GLGizmoTextureDisplacement::update_image_adjust_preview()
-{
-    if (m_adjust_preview_source.empty())
-        return;
-
-    // Collect a finished pass. wait_for(0) rather than get() outright: this runs inside the frame, and
-    // blocking on the worker here would hand back to the UI thread the very stall the worker exists to
-    // spare it.
-    if (m_adjust_preview_job.valid() &&
-        m_adjust_preview_job.wait_for(std::chrono::seconds(0)) == std::future_status::ready) {
-        const DecodedHeightTexture adjusted = m_adjust_preview_job.get();
-        m_adjust_preview_job                = {};
-        if (std::unique_ptr<GLTexture> tex = upload_height_thumbnail(adjusted, ADJUST_PREVIEW_MAX_PX)) {
-            m_adjust_preview_tex   = std::move(tex);
-            m_adjust_preview_shown = m_adjust_preview_running;
-            m_adjust_preview_valid = true;
-        }
-    }
-
-    // One pass at a time: whatever the sliders did while it ran is picked up by the next launch, so a
-    // drag collapses to the value the sliders ended on instead of queuing one pass per frame.
-    if (!m_adjust_preview_job.valid() && m_adjust != m_adjust_preview_shown) {
-        m_adjust_preview_running = m_adjust;
-        // Captured by value: the pass must not read members the UI thread goes on editing while it runs.
-        m_adjust_preview_job = std::async(std::launch::async,
-                                          [src = m_adjust_preview_source, adj = m_adjust_preview_running] {
-                                              return apply_texture_adjustments(src, adj);
-                                          });
-    }
-
-    // A pass in flight has no other way to get its result on screen: without a redraw request the canvas
-    // can sit idle, and the preview would only catch up on the next unrelated frame.
-    if (m_adjust_preview_job.valid())
-        m_parent.set_as_dirty();
-}
-
-void GLGizmoTextureDisplacement::commit_image_adjust(TextureDisplacementLayer &layer)
-{
-    if (m_adjust_source.empty() || m_adjust.identity()) {
-        // Nothing was changed, so there is nothing to save.
-        close_image_adjust();
-        return;
-    }
-
-    // The full-size pass, once: 13-19 ms grayscale / 40-60 ms colour on a 1024x1024 with every knob
-    // engaged. Run on the UI thread deliberately, unlike the live preview: this is a single click, and the
-    // rebuild that follows it - a CPU mesh displacement of the painted patch - is already an order of
-    // magnitude more work, synchronously, so moving only this off the thread would buy nothing a user
-    // could perceive.
-    const DecodedHeightTexture adjusted = apply_texture_adjustments(m_adjust_source, m_adjust);
-
-    std::string                              error;
-    const std::string                        stem  = layer.name.empty() ? std::string("texture") : layer.name;
-    const std::optional<TextureLibraryEntry> entry = save_texture_to_library(adjusted, stem, error);
-    if (!entry) {
-        show_error(nullptr, error);
-        return; // the panel stays open, and the layer keeps the live adjustment: the edit is not lost
-    }
-
-    // Cleared *before* the layer is pointed at the new file, and this ordering is the whole correctness of
-    // the commit: the saved image already has the adjustment baked into its pixels, so leaving
-    // preview_adjust set would apply brightness, contrast and the rest a second time on top of itself.
-    layer.preview_adjust = TextureAdjustments{};
-    // set_layer_texture() does the rest - the name, the recently-used ordering, a fresh image_data buffer
-    // (which is what invalidates every cache keyed by the old pointer), the undo snapshot and the rebuild.
-    set_layer_texture(layer, *entry);
-
-    close_image_adjust();
-}
-
-void GLGizmoTextureDisplacement::render_image_adjust_window(const ImVec2 &panel_min, const ImVec2 &panel_max)
-{
-    if (m_adjust_slot < 0)
-        return;
-
-    ModelVolume *mv = texture_volume();
-    // A different volume is selected than the one this panel was opened on. Slots are numbered per
-    // volume, so looking m_adjust_slot up here would find an unrelated layer rather than nothing.
-    if (mv == nullptr || mv->id().id != m_adjust_volume_id) {
-        close_image_adjust();
-        return;
-    }
-
-    TextureDisplacementLayer *layer = nullptr;
-    for (TextureDisplacementLayer &l : mv->texture_displacement_layers)
-        if (l.slot == m_adjust_slot)
-            layer = &l;
-    if (layer == nullptr) {
-        // The layer went away under the panel (removed, or merged away by an undo).
-        close_image_adjust();
-        return;
-    }
-
-    // The layer's image can be swapped from the texture picker while this panel is open - the panel is a
-    // window now, so the rest of the gizmo stays usable behind it. Re-read the source when that happens,
-    // keeping the slider positions: the user is adjusting this layer, and the 3D view has already moved to
-    // the new image (decode_height_texture() reads layer.image_data, which changed), so re-reading here is
-    // also what keeps the panel's photo and the model showing the same thing.
-    if (layer->image_data.get() != m_adjust_source_image && !load_image_adjust_source(*layer)) {
-        close_image_adjust(); // the new image cannot be decoded; nothing left to adjust
-        return;
-    }
-
-    const float img_w = std::round(m_imgui->scaled(16.f));
-    const float gap   = m_imgui->scaled(0.5f);
-    // Placed beside the panel on first appearance only, and left wherever the user drags it after that -
-    // it is a window, not a popup, so its position is theirs to keep.
-    const float win_w = img_w + 2.f * ImGui::GetStyle().WindowPadding.x;
-    const bool  left  = panel_min.x - gap - win_w >= 0.f;
-    ImGui::SetNextWindowPos(ImVec2(left ? panel_min.x - gap - win_w : panel_max.x + gap,
-                                   panel_min.y + m_imgui->scaled(4.f)), ImGuiCond_Appearing);
-
-    bool keep_open = true;
-    if (!ImGui::Begin((_u8L("Adjust image") + "##texture_adjust").c_str(), &keep_open,
-                      ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoCollapse)) {
-        ImGui::End();
-        if (!keep_open)
-            close_image_adjust();
-        return;
-    }
-
-    // Collect a finished pass and start one for the current slider values before the image is drawn, so
-    // the newest available result is what lands on screen this frame.
-    update_image_adjust_preview();
-
-    // The photo itself, at the image's own aspect so a non-square texture is not stretched.
-    const float aspect = m_adjust_source.height > 0 ? float(m_adjust_source.width) / float(m_adjust_source.height) : 1.f;
-    const float img_h  = std::round(img_w / std::max(0.05f, aspect));
-    if (m_adjust_preview_valid && m_adjust_preview_tex)
-        ImGui::Image((ImTextureID) (intptr_t) m_adjust_preview_tex->get_id(), ImVec2(img_w, img_h));
-    else
-        ImGui::Dummy(ImVec2(img_w, img_h));
-
-    // The label column is sized off the widest of the five labels, so the tracks line up whatever the
-    // translation does to their lengths.
-    float label_w = 0.f;
-    for (const wxString &l : { _L("Brightness"), _L("Contrast"), _L("Sharpness"), _L("Blur"), _L("Hue") })
-        label_w = std::max(label_w, ImGui::CalcTextSize(into_u8(l).c_str()).x);
-    label_w += m_imgui->scaled(1.2f);
-    // An explicit track width rather than a fill-to-the-right one: this window is AlwaysAutoResize, so its
-    // width comes from its content, and an item asking for "whatever is left" would make the width depend
-    // on itself. The image above sets the content width, and the sliders match it.
-    const float slider_w = std::max(m_imgui->scaled(4.f), img_w - label_w);
-
-    const auto row = [&](const char *id, const wxString &label, float *v, float v_min, float v_max,
-                         const char *format, bool enabled, const std::string &tip) {
-        const float x0 = ImGui::GetCursorPosX();
-        ImGui::AlignTextToFramePadding();
-        m_imgui->text(label);
-        ImGui::SameLine();
-        ImGui::SetCursorPosX(std::max(ImGui::GetCursorPosX(), x0 + label_w));
-        ImGui::SetNextItemWidth(slider_w);
-        m_imgui->disabled_begin(!enabled);
-        ImGui::SliderFloat(id, v, v_min, v_max, format, ImGuiSliderFlags_AlwaysClamp);
-        m_imgui->disabled_end();
-        // Only on an enabled row: a disabled item does not report hover, so a tooltip on one would never
-        // be shown. What has to be said about a disabled slider is written out below it instead.
-        if (enabled && !tip.empty() && ImGui::IsItemHovered())
-            m_imgui->tooltip(tip, ImGui::GetFontSize() * 20.f);
-    };
-
-    row("##adj_brightness", _L("Brightness"), &m_adjust.brightness, -1.f, 1.f, "%.2f", true, {});
-    row("##adj_contrast", _L("Contrast"), &m_adjust.contrast, -1.f, 1.f, "%.2f", true, {});
-    row("##adj_sharpness", _L("Sharpness"), &m_adjust.sharpness, 0.f, 1.f, "%.2f", true,
-        _u8L("Brings out the finest detail in the image. Applied after Blur, so the two can be used "
-             "together: blur away the speckle, then sharpen the edges that remain."));
-    row("##adj_blur", _L("Blur"), &m_adjust.blur, 0.f, 1.f, "%.2f", true,
-        _u8L("Blurs the image itself. The layer's own Smoothing slider softens the relief without altering "
-             "the image, and is the one to reach for first."));
-    // Grey has no hue to turn, and the shipped library is grayscale - so on most textures this is a
-    // slider that would visibly do nothing. Disabled with the reason given, rather than hidden.
-    const bool has_color = m_adjust_source.has_color();
-    row("##adj_hue", _L("Hue"), &m_adjust.hue_deg, -180.f, 180.f, "%.0f°", has_color, {});
-    if (!has_color) {
-        ImGui::PushTextWrapPos(ImGui::GetCursorPosX() + img_w);
-        ImGui::TextDisabled("%s", _u8L("This texture is grayscale, so it has no hue to shift.").c_str());
-        ImGui::PopTextWrapPos();
-    }
-
-    if (m_imgui->button(_L("Reset")))
-        m_adjust = TextureAdjustments{};
-
-    // Hand the sliders to the layer, which is what puts the adjusted image in front of the displacement:
-    // decode_height_texture() applies preview_adjust, so the relief, the colour and the thumbnails all
-    // follow from here. Written every frame rather than only on a change, so an undo snapshot or a
-    // reselection that resets the layer cannot leave the model showing an adjustment the panel has moved
-    // on from.
-    layer->preview_adjust = m_adjust;
-    if (m_adjust != m_adjust_applied) {
-        m_adjust_applied = m_adjust;
-        // Marked dirty rather than rebuilt here: the panel's own flag is consumed by the main panel's
-        // "rebuild once the mouse is released" rule, so dragging a slider recomputes the displacement
-        // once, on release, instead of on every frame of the drag. That is what keeps the UI responsive
-        // while a full-size resample and a mesh displacement happen behind it.
-        m_preview_params_dirty = true;
-        // This window is drawn after the block that consumes that flag, so the rebuild happens on a later
-        // frame - which means there has to *be* one. Cheap insurance: a slider release that generated no
-        // further canvas event would otherwise leave the flag set and the model unchanged until something
-        // unrelated redrew.
-        m_parent.set_as_dirty();
-    }
-
-    ImGui::Separator();
-    m_imgui->text_wrapped(_u8L("The model updates when you release a slider. Save as copy writes the "
-                               "adjusted image to your texture library and points this layer at it."), img_w);
-
-    const bool cancel = m_imgui->button(_L("Cancel"));
-    ImGui::SameLine();
-    // Nothing to save until a slider has actually moved.
-    m_imgui->disabled_begin(m_adjust.identity());
-    const bool as_copy = m_imgui->button(_L("Save as copy"));
-    m_imgui->disabled_end();
-
-    ImGui::End();
-
-    if (cancel || !keep_open)
-        close_image_adjust();
-    else if (as_copy)
-        commit_image_adjust(*layer);
-}
 
 void GLGizmoTextureDisplacement::remove_texture_layer(int slot)
 {
@@ -4371,7 +4082,6 @@ void GLGizmoTextureDisplacement::swap_layer_slots(int slot_a, int slot_b)
     std::swap(m_thumbnails[a], m_thumbnails[b]);
     std::swap(m_thumbnail_source[a], m_thumbnail_source[b]);
     std::swap(m_thumbnail_smoothing[a], m_thumbnail_smoothing[b]);
-    std::swap(m_thumbnail_adjust[a], m_thumbnail_adjust[b]);
     std::swap(m_layer_expanded[a], m_layer_expanded[b]);
     if (m_active_layer_slot == slot_a)
         m_active_layer_slot = slot_b;
@@ -5200,7 +4910,8 @@ ColorQuantizeFn GLGizmoTextureDisplacement::make_palette_quantizer(const std::ve
 
 TextureDisplacementPrepareResult GLGizmoTextureDisplacement::prepare_mesh(
     const indexed_triangle_set &base, const TextureDisplacementFacetsData &masks,
-    const std::vector<TextureDisplacementLayer> &layers, const TextureDisplacementPrepareParams &params,
+    const std::vector<TextureDisplacementLayer> &layers, const std::vector<Vec2f> &model_uv,
+    const TextureDisplacementPrepareParams &params,
     const TextureColorSettings &color_settings, const DisplacementProgressFn &progress,
     BakeStageRecorder *debug)
 {
@@ -5227,6 +4938,13 @@ TextureDisplacementPrepareResult GLGizmoTextureDisplacement::prepare_mesh(
     bool                          had_paint = false;
     for (const TriangleSelector::TriangleSplittingData &m : masks)
         had_paint = had_paint || TriangleSelector::has_facets(m, EnforcerBlockerType::ENFORCER);
+    // The model's own UV channel for whatever `mesh` currently is. Every stage below keeps the input's
+    // surface - it evens out, refines or cuts the triangles lying on it - so each corner reads its uv
+    // straight off `base`'s channel at its own position instead of being carried stage by stage, which
+    // would compound each stage's approximation. Untouched while nothing has replaced the mesh yet.
+    const auto uv_now = [&]() {
+        return (model_uv.empty() || !changed) ? model_uv : transfer_uv_channel(base, model_uv, mesh.its);
+    };
     if (!report(1))
         return out;
 
@@ -5273,9 +4991,11 @@ TextureDisplacementPrepareResult GLGizmoTextureDisplacement::prepare_mesh(
             // Feature-adaptive: sample the combined displacement so refinement follows texture
             // curvature. A null sampler (only LSCM layers, or nothing decodable) falls back to the
             // length baseline alone.
+            const std::vector<Vec2f> uv_stage = uv_now();
+            const std::vector<Vec2f> *uv_ptr  = uv_stage.empty() ? nullptr : &uv_stage;
             HeightFieldSampler sampler;
             if (params.subdiv_feature)
-                sampler = make_combined_displacement_sampler(mesh.its, layers, current);
+                sampler = make_combined_displacement_sampler(mesh.its, layers, current, uv_ptr);
             // Colour boundaries need triangles of their own - the chord test cannot see them, since
             // the height field is perfectly smooth across a change of filament.
             ColorFieldSampler color;
@@ -5283,7 +5003,7 @@ TextureDisplacementPrepareResult GLGizmoTextureDisplacement::prepare_mesh(
             // boundaries are refined where the bake will actually change filament.
             if (params.subdiv_color_edge_mm > 0.f && !color_settings.empty())
                 color = make_combined_color_sampler(mesh.its, layers, current, make_palette_quantizer(color_settings.palette),
-                                                    make_palette_quantizer(color_settings.palette_pure));
+                                                    make_palette_quantizer(color_settings.palette_pure), uv_ptr);
             // The refinement follows perceived colour: a mix is one colour here, however the slicer
             // interleaves its filaments layer by layer.
             // "Min edge" is a feature-mode control (it is the floor the curvature test refines down
@@ -5342,8 +5062,10 @@ TextureDisplacementPrepareResult GLGizmoTextureDisplacement::prepare_mesh(
                 std::vector<uint8_t> cut_region(mesh.its.indices.size(), 0);
                 for (size_t i = 0; i < cut_region.size() && i < source.size(); ++i)
                     cut_region[i] = (region[size_t(source[i])] & REFINE_PAINTED) ? 1 : 0;
+                const std::vector<Vec2f> uv_refined = uv_now();
                 const HeightFieldSampler refined_sampler =
-                    make_combined_displacement_sampler(mesh.its, layers, current);
+                    make_combined_displacement_sampler(mesh.its, layers, current,
+                                                        uv_refined.empty() ? nullptr : &uv_refined);
                 std::vector<int>     cut_source;
                 size_t               cuts = 0;
                 indexed_triangle_set cut = cut_mesh_at_steps(mesh.its, cut_region, refined_sampler,
@@ -5367,6 +5089,7 @@ TextureDisplacementPrepareResult GLGizmoTextureDisplacement::prepare_mesh(
     if (!report(100) || !changed)
         return out; // an empty result: nothing to commit, which is not a failure
 
+    out.uv    = uv_now();
     out.mesh  = std::move(mesh.its);
     out.masks = std::move(current);
     return out;
@@ -5635,7 +5358,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_thumbnail(const TextureDisplace
 
     const size_t slot = size_t(layer.slot);
     if (m_thumbnails[slot] && m_thumbnail_source[slot] == layer.image_data.get() &&
-        m_thumbnail_smoothing[slot] == layer.smoothing && m_thumbnail_adjust[slot] == layer.preview_adjust)
+        m_thumbnail_smoothing[slot] == layer.smoothing)
         return m_thumbnails[slot].get();
 
     // Reuses the already-decoded, already-cached grayscale pixels (see decode_height_texture()'s
@@ -5649,7 +5372,6 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_thumbnail(const TextureDisplace
     m_thumbnails[slot]          = std::move(texture);
     m_thumbnail_source[slot]    = layer.image_data.get();
     m_thumbnail_smoothing[slot] = layer.smoothing;
-    m_thumbnail_adjust[slot]    = layer.preview_adjust;
     return m_thumbnails[slot].get();
 }
 
@@ -5657,8 +5379,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_color_texture(const TextureDisp
 {
     if (layer.empty() || !layer.color_enabled)
         return nullptr;
-    if (m_color_tex && m_color_tex_source == layer.image_data.get() && m_color_tex_smoothing == layer.smoothing &&
-        m_color_tex_adjust == layer.preview_adjust)
+    if (m_color_tex && m_color_tex_source == layer.image_data.get() && m_color_tex_smoothing == layer.smoothing)
         return m_color_tex.get();
 
     std::unique_ptr<GLTexture> texture = upload_color_texture(decode_height_texture(layer), HEIGHT_TEX_MAX_PX);
@@ -5670,7 +5391,6 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_color_texture(const TextureDisp
     m_color_tex           = std::move(texture);
     m_color_tex_source    = layer.image_data.get();
     m_color_tex_smoothing = layer.smoothing;
-    m_color_tex_adjust    = layer.preview_adjust;
     return m_color_tex.get();
 }
 
@@ -5681,8 +5401,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_height_texture(const TextureDis
 
     // One slot, not one per layer: the preview shader only ever shades the *active* layer, so a single
     // full-resolution upload is enough and the VRAM cost stays at one texture rather than eight.
-    if (m_height_tex && m_height_tex_source == layer.image_data.get() && m_height_tex_smoothing == layer.smoothing &&
-        m_height_tex_adjust == layer.preview_adjust)
+    if (m_height_tex && m_height_tex_source == layer.image_data.get() && m_height_tex_smoothing == layer.smoothing)
         return m_height_tex.get();
 
     std::unique_ptr<GLTexture> texture = upload_height_thumbnail(decode_height_texture(layer), HEIGHT_TEX_MAX_PX);
@@ -5692,7 +5411,6 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_height_texture(const TextureDis
     m_height_tex           = std::move(texture);
     m_height_tex_source    = layer.image_data.get();
     m_height_tex_smoothing = layer.smoothing;
-    m_height_tex_adjust    = layer.preview_adjust;
     return m_height_tex.get();
 }
 
@@ -6023,6 +5741,8 @@ void GLGizmoTextureDisplacement::queue_prepare(const TextureDisplacementPrepareP
     input.layers        = mv->texture_displacement_layers;
     input.params        = params;
     input.snapshot_name = snapshot_name;
+    if (mv->has_texture_uv())
+        input.model_uv = mv->texture_uv;
     if (params.subdiv_color_edge_mm > 0.f)
         input.color = color_settings_for(*mv);
 
@@ -6749,7 +6469,7 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                 ImGui::SameLine();
 
                 const std::string not_painted = _u8L("not painted");
-                const float right_w = (painted ? 0.f : ImGui::CalcTextSize(not_painted.c_str()).x + gap_s) + 4.f * frame_h + 3.f * gap_s;
+                const float right_w = (painted ? 0.f : ImGui::CalcTextSize(not_painted.c_str()).x + gap_s) + 3.f * frame_h + 2.f * gap_s;
                 const float name_w  = std::max(frame_h, ImGui::GetWindowContentRegionMax().x - card_pad - ImGui::GetCursorPosX() - gap_s - right_w);
                 ImGui::PushStyleColor(ImGuiCol_HeaderHovered, ImVec4(orca.x, orca.y, orca.z, 0.2f));
                 ImGui::PushStyleColor(ImGuiCol_HeaderActive, ImVec4(orca.x, orca.y, orca.z, 0.35f));
@@ -6763,16 +6483,6 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                     ImGui::SameLine();
                     ImGui::TextDisabled("%s", not_painted.c_str());
                 }
-                // Between the name and the order arrows: it acts on the image the name refers to, so it
-                // belongs with the name rather than with the controls that reorder the stack.
-                ImGui::SameLine();
-                m_imgui->disabled_begin(busy || layer.empty());
-                if (icon_button(613 + layer.slot, "cog.svg", frame_h, _L("Adjust image"),
-                                _u8L("Brightness, contrast, sharpness, blur and hue, shown on the image and on the "
-                                     "model as you set them. Save as copy writes the result to your texture library "
-                                     "and points this layer at it.")))
-                    open_image_adjust(layer);
-                m_imgui->disabled_end();
                 ImGui::SameLine();
                 m_imgui->disabled_begin(busy || li == 0);
                 if (icon_button(611, "texture_displacement_move_up.svg", frame_h, _L("Move up"), _L("Move up - applied earlier"))) {
@@ -6801,10 +6511,22 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
             m_preview_params_dirty |= float_row("##depth", _L("Depth"), &layer.depth_mm, 0.01f, 10.f, "%.3f mm", true, card_pad);
             hover_tip(_u8L("Height of the relief: how far white in the texture lifts the surface, in "
                            "millimetres. Black does not move it at all, unless Midlevel says otherwise."));
-            m_preview_params_dirty |= float_row("##tile_size", _L("Tile size"), &layer.tiling_scale, 0.2f, 200.f, "%.2f mm", true, card_pad);
-            hover_tip(_u8L("How wide one copy of the texture is on the model. Smaller repeats the pattern "
-                           "more often and makes its detail finer; with Tile off, this is the size of the "
-                           "single copy."));
+            // Mapped by the model's own UV layout there is no millimetre scale to set: the layout is the
+            // placement (see TextureProjectionMethod::ModelUV), so the slider would move nothing.
+            const bool tile_size_na = layer.projection_method == TextureProjectionMethod::ModelUV;
+            m_imgui->disabled_begin(tile_size_na);
+            m_preview_params_dirty |= float_row("##tile_size", _L("Tile size"), &layer.tiling_scale, 0.2f, 200.f,
+                                                "%.2f mm", true, card_pad);
+            m_imgui->disabled_end();
+            // AllowWhenDisabled, or the one case that needs explaining is the one that cannot be hovered.
+            if (ImGui::IsItemHovered(ImGuiHoveredFlags_AllowWhenDisabled))
+                m_imgui->tooltip(tile_size_na ?
+                                     _u8L("Mapped by the model's own UV layout, which is already the placement - one "
+                                          "copy of the texture covers it exactly, so there is no tile size to set.") :
+                                     _u8L("How wide one copy of the texture is on the model. Smaller repeats the "
+                                          "pattern more often and makes its detail finer; with Tile off, this is the "
+                                          "size of the single copy."),
+                                 wrap_w);
             m_preview_params_dirty |= float_row("##rotation", _L("Rotation"), &layer.rotation_deg, 0.f, 360.f, "%.0f°", false, card_pad);
             hover_tip(_u8L("Turns the texture on the surface, in degrees - for lining a pattern up with an "
                            "edge of the model."));
@@ -6911,7 +6633,7 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                     }
                 }
 
-                // Mapping, as five icons in TextureProjectionMethod's own order.
+                // Mapping, as one icon per TextureProjectionMethod, in the enum's own order.
                 {
                     const float x0 = ImGui::GetCursorPosX();
                     ImGui::AlignTextToFramePadding();
@@ -6939,13 +6661,26 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                         { "texture_displacement_map_view.svg", _L("From view"),
                           _L("From view - projects straight onto the painted area from where you are looking, like a slide "
                              "projector.") },
+                        { "texture_displacement_map_model_uv.svg", _L("Model UV"),
+                          _L("Model UV - uses the texture coordinates the model itself came with, so a texture made for "
+                             "that model lands exactly where it was painted. Nothing is unwrapped, and Tile size does "
+                             "not apply: the model's own layout is the placement.") },
                     };
+                    // Only a volume that actually carries a UV channel can be mapped by it. Shown
+                    // greyed out rather than hidden, so the reason is visible instead of the control
+                    // simply being missing.
+                    const wxString model_uv_na =
+                        (mv != nullptr && mv->has_texture_uv()) ?
+                            wxString() :
+                            _L("This model carries no texture coordinates of its own. Only a model imported with a UV "
+                               "channel - a textured OBJ, say - can be mapped by them.");
                     for (int mi = 0; mi < int(IM_ARRAYSIZE(mappings)); ++mi) {
                         if (mi > 0)
                             ImGui::SameLine(0.f, gap_s);
                         const auto method = static_cast<TextureProjectionMethod>(mi);
+                        const wxString na = (method == TextureProjectionMethod::ModelUV) ? model_uv_na : wxString();
                         if (icon_toggle(830 + mi, mappings[mi].file, layer.projection_method == method, icon_sm, mappings[mi].label,
-                                        mappings[mi].tip) &&
+                                        mappings[mi].tip, na) &&
                             layer.projection_method != method) {
                             // Capture the current view the moment "From view" is chosen, so it does something
                             // sensible immediately rather than projecting from a stale/default direction.
@@ -7075,18 +6810,33 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                     ImGui::SameLine();
                     ImGui::SetCursorPosX(std::max(ImGui::GetCursorPosX(), x0 + label_w));
                     const std::string blend_add      = _u8L_CONTEXT("Add", "Texture Displacement");
+                    const std::string blend_override  = _u8L_CONTEXT("Override", "Texture Displacement");
                     const std::string blend_subtract = _u8L_CONTEXT("Subtract", "Texture Displacement");
                     const std::string blend_multiply = _u8L_CONTEXT("Multiply", "Texture Displacement");
                     const std::string blend_divide   = _u8L("Divide");
-                    const char *blend_items[] = { blend_add.c_str(), blend_subtract.c_str(), blend_multiply.c_str(), blend_divide.c_str() };
+                    const char *blend_items[] = { blend_add.c_str(), blend_override.c_str(), blend_subtract.c_str(),
+                                                  blend_multiply.c_str(), blend_divide.c_str() };
+                    // The combo's order is the panel's, not the enum's - Override reads as the sibling of Add and
+                    // belongs next to it, while TextureBlendMode's numbering is fixed by what projects already
+                    // store. Hence the explicit mapping rather than a cast of the index.
+                    static const TextureBlendMode blend_modes[] = { TextureBlendMode::Add, TextureBlendMode::Override,
+                                                                    TextureBlendMode::Subtract, TextureBlendMode::Multiply,
+                                                                    TextureBlendMode::Divide };
+                    static_assert(IM_ARRAYSIZE(blend_items) == IM_ARRAYSIZE(blend_modes),
+                                  "every Blend entry needs its mode");
                     // The first layer has nothing before it to combine with - build_texture_displacement() makes it
                     // add regardless - so its combo shows Add and cannot be changed.
                     const bool base_layer = li == 0;
-                    int        blend_mode = base_layer ? 0 : static_cast<int>(layer.blend_mode);
+                    int        blend_mode = 0;
+                    if (!base_layer)
+                        for (int bi = 0; bi < int(IM_ARRAYSIZE(blend_modes)); ++bi)
+                            if (blend_modes[bi] == layer.blend_mode)
+                                blend_mode = bi;
                     ImGui::SetNextItemWidth(-(card_pad + gap_s + icon_sm));
                     m_imgui->disabled_begin(base_layer);
-                    if (scoped_combo("##blend_mode", &blend_mode, blend_items, IM_ARRAYSIZE(blend_items)) && !base_layer) {
-                        layer.blend_mode       = static_cast<TextureBlendMode>(blend_mode);
+                    if (scoped_combo("##blend_mode", &blend_mode, blend_items, IM_ARRAYSIZE(blend_items)) && !base_layer &&
+                        blend_mode >= 0 && blend_mode < int(IM_ARRAYSIZE(blend_modes))) {
+                        layer.blend_mode       = blend_modes[blend_mode];
                         m_preview_params_dirty = true;
                     }
                     m_imgui->disabled_end();
@@ -7094,10 +6844,11 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                         m_imgui->tooltip(base_layer ?
                                              _u8L("The base layer has nothing beneath it to combine with, so it always adds.") :
                                              _u8L("What this layer does where it overlaps the ones below. Add and "
-                                                  "Subtract pile relief on or carve it away. Multiply and Divide scale "
-                                                  "what is underneath, which turns this layer into a mask over it - "
-                                                  "there, Depth acts as a strength, and 1 mm leaves white areas "
-                                                  "untouched."),
+                                                  "Subtract pile relief on or carve it away. Override replaces them, "
+                                                  "so only this layer's relief is left where it is painted. Multiply "
+                                                  "and Divide scale what is underneath, which turns this layer into a "
+                                                  "mask over it - there, Depth acts as a strength, and 1 mm leaves "
+                                                  "white areas untouched."),
                                          wrap_w);
 
                     ImGui::SameLine(0.f, gap_s);
@@ -7572,15 +7323,10 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
         set_active_layer(m_picker_slot);
 
     // In this window's scope, where the popup's open request and the popup itself share one ID stack.
-    ImVec2 panel_rect_min, panel_rect_max;
     {
         const ImVec2 win_min = ImGui::GetWindowPos();
         const ImVec2 win_sz  = ImGui::GetWindowSize();
         render_texture_library_popup(win_min, ImVec2(win_min.x + win_sz.x, win_min.y + win_sz.y));
-        // Only recorded here. The image-adjustment panel is a top-level window rather than a popup, so it
-        // cannot be begun inside this one; it is drawn after GizmoImguiEnd() below.
-        panel_rect_min = win_min;
-        panel_rect_max = ImVec2(win_min.x + win_sz.x, win_min.y + win_sz.y);
     }
 
     // ImGui sliders report "changed" continuously on every frame while being dragged, not just once on
@@ -7817,11 +7563,6 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
         m_parent.request_extra_frame();
     }
     GizmoImguiEnd();
-
-    // Outside the gizmo's window, because it is a window of its own: a floating, non-modal panel that
-    // leaves the 3D view live so the relief can be watched while the sliders move. No-op when closed.
-    render_image_adjust_window(panel_rect_min, panel_rect_max);
-
     ImGuiWrapper::pop_toolbar_style();
 
     // Drawn last, over everything, via the foreground draw list: the +/- add-remove sign next to the 3D

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.hpp

@@ -23,7 +23,6 @@
 #include "libslic3r/Point.hpp"
 #include <imgui.h>
 #include <map>
-#include <future>
 #include <memory>
 #include <optional>
 #include "slic3r/GUI/Gizmos/GLGizmoBase.hpp"
@@ -62,6 +61,12 @@ public:
     static TextureDisplacementPrepareResult prepare_mesh(const indexed_triangle_set                  &base,
                                                          const TextureDisplacementFacetsData         &masks,
                                                          const std::vector<TextureDisplacementLayer> &layers,
+                                                         // `base`'s own UV channel, when it has one
+                                                         // (ModelVolume::texture_uv). Resampled onto
+                                                         // the result and reported back in it, and fed
+                                                         // to the samplers so a ModelUV layer drives
+                                                         // the refinement through its own layout.
+                                                         const std::vector<Vec2f>                    &model_uv,
                                                          const TextureDisplacementPrepareParams      &params,
                                                          const TextureColorSettings                  &color_settings,
                                                          const DisplacementProgressFn                &progress,
@@ -400,68 +405,6 @@ private:
     void set_layer_texture(TextureDisplacementLayer &layer, const TextureLibraryEntry &entry);
     void import_custom_texture(TextureDisplacementLayer &layer);
 
-    // ---- The image-adjustment panel ----
-    //
-    // Brightness/contrast/sharpness/blur/hue over one layer's image, shown on the image itself and
-    // updating as the sliders move. What it produces is not a set of layer parameters: it replaces the
-    // layer's *image*, so the adjusted pixels feed the colour and the displacement together and a
-    // brightness change moves the relief too (see TextureAdjustments).
-    //
-    // An ordinary floating window rather than a popup, and deliberately so. A popup dims the canvas
-    // behind it and closes on any click outside itself, which between them make it impossible to watch the
-    // relief change on the model - which is the whole point of adjusting the image here rather than in an
-    // image editor. A window leaves the 3D view live, clickable and orbitable while the panel is open.
-    void render_image_adjust_window(const ImVec2 &panel_min, const ImVec2 &panel_max);
-    // Opens the panel for `layer`, decoding its image into m_adjust_source. Sliders never re-decode
-    // the PNG.
-    void open_image_adjust(const TextureDisplacementLayer &layer);
-    // Reads `layer`'s stored image into the panel's source buffers and records which image it came from.
-    // Called when the panel opens and again whenever the layer's image is swapped under it, which is why
-    // it leaves the slider values alone. False when the image cannot be decoded.
-    bool load_image_adjust_source(const TextureDisplacementLayer &layer);
-    // Resolves the panel: writes the adjusted image into the user's texture library as a new file and
-    // points `layer` at it, which is the only way an adjustment becomes permanent. Closes the panel.
-    void commit_image_adjust(TextureDisplacementLayer &layer);
-    // Closes the panel and reverts the layer's live preview_adjust to identity, so every exit that is not
-    // a commit - Cancel, the window's close button, the gizmo closing - leaves the layer as it was found.
-    void close_image_adjust();
-    // Collects a finished preview and starts one for the current slider values. One at a time, so a drag
-    // coalesces into "whatever the sliders last said" instead of a queue of superseded frames.
-    void update_image_adjust_preview();
-
-    int                m_adjust_slot = -1; // the layer the panel is open for; -1 when closed
-    TextureAdjustments m_adjust;           // what the sliders currently say
-    // What the layer's live preview_adjust was last set from, so a slider move can be told from a frame in
-    // which nothing happened and only the former asks the displacement to be recomputed.
-    TextureAdjustments m_adjust_applied;
-
-    // The layer's image as it was when the panel opened, and a small copy of it. The sliders are applied
-    // to the small copy for the live preview and to the full-size one exactly once, on commit. Measured on
-    // a 1024x1024 with every knob engaged, a full-size pass costs 13-19 ms grayscale and 40-60 ms in
-    // colour (130-190 ms at 2048 in colour) - far too much to repeat per slider frame. The same pass on a
-    // 384 px copy is 3-4 ms / 9-12 ms, and that is all the preview box can show anyway.
-    DecodedHeightTexture m_adjust_source;
-    DecodedHeightTexture m_adjust_preview_source;
-    // Which image_data the two buffers above were decoded from, so the panel can notice the layer's image
-    // being swapped from the texture picker while it is open and re-read it. Compared, never dereferenced.
-    const void          *m_adjust_source_image = nullptr;
-    // And which volume the panel was opened on. Slot numbers are per volume, so without this a change of
-    // selection would silently rebind the open panel to whichever layer happens to hold the same slot on
-    // the newly selected object - a different image, under a panel the user opened for this one.
-    size_t               m_adjust_volume_id = 0;
-    // The preview image on screen, re-uploaded whenever a background pass finishes.
-    std::unique_ptr<GLTexture> m_adjust_preview_tex;
-
-    // The live preview runs on its own thread rather than on the UI thread or on the plater's job
-    // worker. Not the UI thread because even the small pass is milliseconds and this runs while a slider
-    // is being dragged; not the job worker because that is a single FIFO shared with Bake and the
-    // displacement preview (see queue_preview_job()), where a per-frame image filter would sit behind -
-    // and delay - multi-second mesh work.
-    std::future<DecodedHeightTexture> m_adjust_preview_job;
-    TextureAdjustments                m_adjust_preview_running; // what the in-flight pass is computing
-    TextureAdjustments                m_adjust_preview_shown;   // what m_adjust_preview_tex holds
-    bool                              m_adjust_preview_valid = false;
-
     // Paint / Erase, from the panel. See get_left_button_state_type().
     bool m_erase_mode = false;
     // Per slot: whether the layer's card shows every setting or only Depth, Tile size and Rotation.
@@ -881,18 +824,31 @@ private:
     // Merges chart `b`'s join group into chart `a`'s (materialising `groups` to `chart_count` first).
     static void      join_island_groups(std::vector<int> &groups, int a, int b, int chart_count);
     // Final per-vertex texture uv for the projections the shader can't reconstruct itself - LSCM (an
-    // unwrap) and ViewProjected (a projector plane the shader doesn't know). One entry per patch/base
-    // vertex, already through apply_uv_transform(). Empty for Triplanar/Cylindrical/Spherical, which
-    // the shader projects on its own. Shared by the shaded preview and the UV-check overlay.
+    // unwrap), ModelUV (the model's own channel) and ViewProjected (a projector plane the shader
+    // doesn't know). One entry per patch/base vertex, already through apply_uv_transform(). Empty for
+    // Triplanar/Cylindrical/Spherical, which the shader projects on its own. Shared by the shaded
+    // preview and the UV-check overlay.
+    //
+    // `patch_source` maps each patch triangle back to its base-mesh triangle
+    // (TriangleSelector::get_facets_strict()'s out_source). Only ModelUV needs it - its channel is per
+    // base triangle - and without it a ModelUV layer reports no uvs and the preview falls back.
     std::vector<Vec2f> compute_layer_vertex_uvs(const indexed_triangle_set &patch,
-                                                const TextureDisplacementLayer &layer) const;
+                                                const TextureDisplacementLayer &layer,
+                                                const std::vector<int> *patch_source = nullptr) const;
     // The same, but three UVs per patch triangle (corner 0..2 of triangle i at 3i..3i+2). This is what
     // the flat, unshared-vertex preview meshes actually want: under LSCM a seam vertex has a different
     // UV in each island it borders, so collapsing to one per vertex handed a triangle at an unjoined
     // seam its neighbour's placement - one visibly skewed triangle per face. Every other projection is
     // single-valued per point, so there a corner's UV is just its vertex's.
     std::vector<Vec2f> compute_layer_corner_uvs(const indexed_triangle_set &patch,
-                                                const TextureDisplacementLayer &layer) const;
+                                                const TextureDisplacementLayer &layer,
+                                                const std::vector<int> *patch_source = nullptr) const;
+    // The model's own channel over `local_patch`, already through apply_uv_transform() - three per
+    // patch triangle. Empty when the volume has no channel, or when `patch_source` is missing. Shared
+    // by the two functions above so the per-vertex and per-corner forms can never disagree.
+    std::vector<Vec2f> model_uv_corners(const indexed_triangle_set &local_patch,
+                                        const TextureDisplacementLayer &layer,
+                                        const std::vector<int> *patch_source) const;
     // The in-shader projection for `layer` (0 Triplanar, 1 Cylindrical, 2 Spherical) plus, for the two
     // wrapping ones, the patch centroid and cylinder axis they wrap around - in the texture frame the
     // shaders project in. Taken from the bake's own texture_displacement_patch_frame(), so a preview
@@ -941,7 +897,6 @@ private:
     enum class UVBackground { None, Height, Checker };
     UVBackground m_uv_editor_bg = UVBackground::None;
     float        m_uv_editor_bg_smoothing = -1.f; // smoothing the height backdrop was uploaded at
-    TextureAdjustments m_uv_editor_bg_adjust;        // and the live image adjustment it was uploaded at
     const void  *m_uv_editor_bg_image     = nullptr; // the layer image it was uploaded from
     // Per-chart distortion heatmap colour for the UV pane (#7/#14), computed once when the unwrap is
     // re-solved (relative stretch doesn't change when islands are merely moved), fed to the canvas only
@@ -985,10 +940,6 @@ private:
     std::array<const void *, TEXTURE_DISPLACEMENT_MAX_LAYERS>               m_thumbnail_source{};
     // The smoothing each cached thumbnail was built at, so a smoothing change re-uploads it.
     std::array<float, TEXTURE_DISPLACEMENT_MAX_LAYERS>                      m_thumbnail_smoothing{};
-    // And the live image adjustment each was built at, so moving a slider in the image-adjustment panel
-    // re-uploads it. Part of the key for the same reason smoothing is: preview_adjust changes the pixels
-    // decode_height_texture() hands back, and every one of these textures is a copy of those pixels.
-    std::array<TextureAdjustments, TEXTURE_DISPLACEMENT_MAX_LAYERS>          m_thumbnail_adjust{};
 
     // Full-resolution height texture for the preview shader, keyed the same way (see
     // get_layer_height_texture()). A smoothing change re-uploads it, so the fast preview shows the
@@ -996,14 +947,12 @@ private:
     std::unique_ptr<GLTexture> m_height_tex;
     const void                *m_height_tex_source    = nullptr;
     float                      m_height_tex_smoothing = -1.f;
-    TextureAdjustments         m_height_tex_adjust;
 
     // The same, for the layer's *colour*, which the fast preview quantizes per fragment so it shows
     // the image at texel resolution rather than at the mesh's. Null for a grayscale texture.
     std::unique_ptr<GLTexture> m_color_tex;
     const void                *m_color_tex_source    = nullptr;
     float                      m_color_tex_smoothing = -1.f;
-    TextureAdjustments         m_color_tex_adjust;
 
     // Library textures the picker has shown at least once, keyed by file path (see LibraryTexture).
     std::map<std::string, LibraryTexture> m_library_textures;

src/slic3r/GUI/Jobs/TextureDisplacementBakeJob.cpp

@@ -8,6 +8,7 @@
 #include "libslic3r/TextureDisplacement.hpp"
 #include <exception>
 #include <cstddef>
+#include <cstdint>
 #include "slic3r/GUI/Jobs/Worker.hpp"
 #include <memory>
 
@@ -26,6 +27,7 @@
 #include "slic3r/Utils/UndoRedo.hpp"
 #include "libslic3r/ObjectID.hpp"
 #include "libslic3r/TriangleMesh.hpp"
+#include <array>
 
 namespace Slic3r::GUI {
 
@@ -74,7 +76,8 @@ void TextureDisplacementBakeJob::process(Ctl &ctl)
             }
             return true;
         },
-        color, m_input.volume_to_world, nullptr, &m_stats));
+        color, m_input.volume_to_world, nullptr, &m_stats,
+        m_input.model_uv.empty() ? nullptr : &m_input.model_uv));
 
     // Always finish at 100: this is what closes the notification. Reported even on cancel, where
     // build_texture_displacement() returns an empty mesh and finalize() commits nothing.
@@ -126,10 +129,73 @@ void TextureDisplacementBakeJob::finalize(bool canceled, std::exception_ptr &ept
                                                      { mix.a_percent(), 100 - mix.a_percent() });
             });
 
+        // Whether the bake replaced the triangles or only moved the vertices it was given. The classic
+        // path is topology-preserving by contract, so every per-triangle annotation on the volume still
+        // means what it did; the default pipeline refines, cuts and simplifies, so none of them do.
+        // Both are checked: the flag is what the bake promised, the count is what it delivered. Only
+        // the triangles matter - the annotations are per facet and reference no vertex index - so a
+        // vertex count that changed on its own (the bake compacts unreferenced vertices away) is not a
+        // reason to remap anything.
+        const bool topology_changed = m_input.options.pipeline_v2 ||
+                                      m_result.its.indices.size() != m_input.base_mesh.indices.size();
+
+        // Carry the volume's existing paint - the model's own colours above all - across that rebuild.
+        // Without it a bake left the mmu_segmentation_facets bitstream pointing at a triangle set that
+        // no longer existed, which is what scrambled the colours of an imported coloured model even
+        // with colour switched off on every layer and nothing in the bake that was meant to touch them.
+        //
+        // transfer_facet_paint() rather than ModelVolume::restore_painting(): the latter's remap wants
+        // a target triangle overlapping the source paint to within 0.01 mm, which the baked surface is
+        // nowhere near - it has moved by the relief depth. Nothing to do when the topology is intact:
+        // triangle i is still triangle i, so the paint is already exactly right and carrying it at all
+        // could only lose detail.
+        std::array<TriangleSelector::TriangleSplittingData, 4> before;
+        if (topology_changed) {
+            before[0] = volume->supported_facets.get_data();
+            before[1] = volume->seam_facets.get_data();
+            before[2] = volume->mmu_segmentation_facets.get_data();
+            before[3] = volume->fuzzy_skin_facets.get_data();
+        }
+
         volume->set_mesh(std::move(m_result));
         volume->set_new_unique_id();
         volume->calculate_convex_hull();
 
+        if (topology_changed) {
+            const std::array<FacetsAnnotation *, 4> target{ &volume->supported_facets, &volume->seam_facets,
+                                                            &volume->mmu_segmentation_facets,
+                                                            &volume->fuzzy_skin_facets };
+            for (size_t ch = 0; ch < target.size(); ++ch) {
+                const std::vector<uint8_t> state =
+                    transfer_facet_paint(m_input.base_mesh, before[ch], volume->mesh().its);
+                // Nothing was painted in this channel, or there is nothing to paint it onto: either
+                // way the annotation must not keep describing the mesh that is gone.
+                if (state.empty()) {
+                    target[ch]->reset();
+                    continue;
+                }
+                TriangleSelector selector(volume->mesh());
+                bool             any = false;
+                for (size_t i = 0; i < state.size(); ++i)
+                    if (state[i] != 0) {
+                        selector.set_facet(int(i), EnforcerBlockerType(state[i]));
+                        any = true;
+                    }
+                if (any)
+                    target[ch]->set(selector);
+                else
+                    target[ch]->reset();
+            }
+        }
+
+        // The model's own UV channel. Resampled onto a rebuilt mesh from the surface the bake started
+        // from: a displaced vertex came from its foot point on that surface, which is the position its
+        // uv belongs to - so no distance limit, the relief depth is exactly how far it has moved.
+        if (!m_input.model_uv.empty())
+            volume->texture_uv = topology_changed ? transfer_uv_channel(m_input.base_mesh, m_input.model_uv,
+                                                                        volume->mesh().its) :
+                                                     m_input.model_uv;
+
         // Colour lands in mmu_segmentation_facets, merged *over* whatever is already painted there
         // rather than replacing it: a triangle the texture does not colour keeps its existing filament,
         // and one the user never painted at all stays at NONE, which already means "the volume's own
@@ -159,7 +225,6 @@ void TextureDisplacementBakeJob::finalize(bool canceled, std::exception_ptr &ept
         // pipeline, which rebuilds and then simplifies the mesh. A mask left behind against the old
         // topology is exactly what makes the gizmo reload an empty selector over a non-empty mask and
         // then erase it on the next flush - see GLGizmoTextureDisplacement::update_from_model_object().
-        const bool topology_changed = m_input.base_mesh.indices.size() != volume->mesh().its.indices.size();
         for (int slot = 0; slot < int(TEXTURE_DISPLACEMENT_MAX_LAYERS); ++slot) {
             const auto it = std::find_if(m_input.layers.begin(), m_input.layers.end(),
                                          [slot](const TextureDisplacementLayer &l) { return l.slot == slot; });
@@ -219,6 +284,8 @@ void queue_texture_displacement_bake(const ModelVolume &volume, const TextureCol
     input.take_snapshot = take_snapshot;
     input.volume_id  = volume.id();
     input.base_mesh  = volume.mesh().its;
+    if (volume.has_texture_uv())
+        input.model_uv = volume.texture_uv;
     input.layers     = volume.texture_displacement_layers;
     input.options    = volume.texture_displacement_options;
     input.volume_to_world = texture_displacement_volume_to_world(volume);

src/slic3r/GUI/Jobs/TextureDisplacementBakeJob.hpp

@@ -34,6 +34,9 @@ struct TextureDisplacementBakeInput
     // writes the volume's mmu_segmentation_facets - the same per-triangle filament assignment the MMU
     // paint gizmo writes - alongside the displaced geometry.
     TextureColorSettings                  color;
+    // The volume's own UV channel (ModelVolume::texture_uv), empty when it has none: what a ModelUV
+    // layer maps through, and what the commit puts back on the baked mesh.
+    std::vector<Vec2f>                    model_uv;
     // Whether this job pushes its own undo step when it commits. False when the caller has already
     // taken one that is meant to cover the displacement as well - Standard mode's Bake, which remeshes
     // and subdivides first and has to undo as a single action.

src/slic3r/GUI/Jobs/TextureDisplacementDebugJob.cpp

@@ -17,6 +17,7 @@
 #include "slic3r/GUI/Jobs/Worker.hpp"
 #include <memory>
 #include "libslic3r/ObjectID.hpp"
+#include "libslic3r/Point.hpp"
 #include "libslic3r/TriangleMesh.hpp"
 
 namespace Slic3r::GUI {
@@ -52,13 +53,14 @@ void TextureDisplacementDebugJob::process(Ctl &ctl)
 
     indexed_triangle_set          mesh  = m_input.base_mesh;
     TextureDisplacementFacetsData masks = m_input.facets_data;
+    std::vector<Vec2f>            uv    = m_input.model_uv;
 
     // The default pipeline can only move vertices the mesh already has, so its recipe starts with the
     // preparation - which is where "first it remeshes, then it refines" actually happens. The
     // experimental pipeline refines as part of the bake and has nothing to prepare.
     if (m_input.run_prepare && !m_input.options.pipeline_v2) {
         const TextureDisplacementPrepareResult prepared =
-            GLGizmoTextureDisplacement::prepare_mesh(mesh, masks, m_input.layers, m_input.prepare_params,
+            GLGizmoTextureDisplacement::prepare_mesh(mesh, masks, m_input.layers, uv, m_input.prepare_params,
                                                      m_input.color,
                                                      // Preparation is roughly half the run; the bake
                                                      // takes the progress bar from there.
@@ -77,12 +79,14 @@ void TextureDisplacementDebugJob::process(Ctl &ctl)
         if (!prepared.mesh.indices.empty()) {
             mesh  = prepared.mesh;
             masks = prepared.masks;
+            uv    = prepared.uv; // resampled onto the prepared mesh, as the prepare commit stores it
         }
     }
 
     build_texture_displacement(mesh, m_input.layers, masks, m_input.options,
                                [&report](int pct) { return report(50 + pct / 2); },
-                               /* color */ nullptr, m_input.volume_to_world, &recorder);
+                               /* color */ nullptr, m_input.volume_to_world, &recorder, /* stats */ nullptr,
+                               uv.empty() ? nullptr : &uv);
 
     m_stages = recorder.take();
     ctl.update_status(100, status); // always finish at 100: this is what closes the notification
@@ -115,6 +119,8 @@ void queue_texture_displacement_debug(const ModelVolume &volume, const TextureCo
     input.check_topology  = check_topology;
     input.color           = color;
     input.volume_to_world = texture_displacement_volume_to_world(volume);
+    if (volume.has_texture_uv())
+        input.model_uv = volume.texture_uv;
     for (int i = 0; i < int(TEXTURE_DISPLACEMENT_MAX_LAYERS); ++i)
         input.facets_data[size_t(i)] = volume.texture_displacement_facet(i).get_data();
 

src/slic3r/GUI/Jobs/TextureDisplacementDebugJob.hpp

@@ -47,6 +47,9 @@ struct TextureDisplacementDebugInput
     // Only the quantizer is used, and only by the refinement's colour criterion - the debug run
     // produces no colour of its own.
     TextureColorSettings                  color;
+    // The volume's own UV channel (ModelVolume::texture_uv), so the recipe captured here is the one a
+    // ModelUV layer actually bakes through. Empty when the volume has none.
+    std::vector<Vec2f>                    model_uv;
 
     // The edge scan behind the open / non-manifold counts is a sort over every half-edge, which on a
     // multi-million triangle stage costs more than the stage did. On by default because a stage that

src/slic3r/GUI/Jobs/TextureDisplacementPrepareJob.cpp

@@ -46,7 +46,7 @@ void TextureDisplacementPrepareJob::process(Ctl &ctl)
     // idle loop.
     int last_reported = 1;
     m_result = GLGizmoTextureDisplacement::prepare_mesh(m_input.base_mesh, m_input.masks, m_input.layers,
-                                                        m_input.params, m_input.color,
+                                                        m_input.model_uv, m_input.params, m_input.color,
                                                         [&ctl, &status, &last_reported](int percent) {
                                                             if (ctl.was_canceled())
                                                                 return false;
@@ -106,6 +106,10 @@ void TextureDisplacementPrepareJob::finalize(bool canceled, std::exception_ptr &
         volume->restore_painting(saved_painting);
         for (int i = 0; i < int(TEXTURE_DISPLACEMENT_MAX_LAYERS); ++i)
             volume->texture_displacement_facet(i).set_data(std::move(m_result.masks[size_t(i)]));
+        // The model's own UV channel, resampled onto the new mesh by the run. Also put back after
+        // restore_painting(), which resets it along with the extra facets for the same reason: it is
+        // indexed by triangle and the triangles have changed.
+        volume->texture_uv = std::move(m_result.uv);
 
         if (ObjectList *obj_list = wxGetApp().obj_list()) {
             const ModelObjectPtrs &objs = plater->model().objects;

src/slic3r/GUI/Jobs/TextureDisplacementPrepareJob.hpp

@@ -9,6 +9,7 @@
 #include "Job.hpp"
 
 #include "libslic3r/ObjectID.hpp"
+#include "libslic3r/Point.hpp"
 #include "libslic3r/TextureDisplacement.hpp"
 
 namespace Slic3r {
@@ -47,6 +48,10 @@ struct TextureDisplacementPrepareInput
     // skips the colour criterion entirely. Only the *quantizer* is used here: refinement follows
     // perceived colour, never the interleaving that realises a mix.
     TextureColorSettings                  color;
+    // The volume's own UV channel (ModelVolume::texture_uv), empty when it has none. prepare_mesh()
+    // resamples it onto the mesh it produces, and the commit puts it back - like the masks, it is
+    // indexed by triangle and so cannot survive the stages on its own.
+    std::vector<Vec2f>                    model_uv;
     // The undo step the commit opens. Standard mode's Bake names it after the bake, because the
     // displacement job that follows commits into this same step rather than pushing its own.
     std::string                           snapshot_name;

src/slic3r/GUI/Jobs/TextureDisplacementPreviewJob.cpp

@@ -48,7 +48,8 @@ void TextureDisplacementPreviewJob::process(Ctl &ctl)
                                                      (!m_current_generation ||
                                                       m_current_generation->load() == m_generation);
                                           },
-                                          color, m_input.volume_to_world);
+                                          color, m_input.volume_to_world, nullptr, nullptr,
+                                          m_input.model_uv.empty() ? nullptr : &m_input.model_uv);
 }
 
 void TextureDisplacementPreviewJob::finalize(bool canceled, std::exception_ptr &eptr)

src/slic3r/GUI/Jobs/TextureDisplacementPreviewJob.hpp

@@ -29,6 +29,9 @@ struct TextureDisplacementPreviewInput
     // Empty unless a layer is colouring, in which case the preview reports the palette entry per
     // triangle alongside the mesh, so the Normal view shows the colours the bake will produce.
     TextureColorSettings                  color;
+    // The volume's own UV channel (ModelVolume::texture_uv), so a ModelUV layer previews through the
+    // same layout it will bake through. Empty when the volume has none.
+    std::vector<Vec2f>                    model_uv;
 };
 
 // A preview result: the displaced mesh, and - when the input carried a palette - one palette entry per

src/slic3r/GUI/TextureLibrary.cpp

@@ -27,7 +27,6 @@
 #include <wx/mstream.h>
 
 #include "libslic3r/PNGReadWrite.hpp"
-#include "libslic3r/TextureDisplacement.hpp"
 #include "libslic3r/Utils.hpp"
 
 #include "libslic3r/AppConfig.hpp"
@@ -159,28 +158,6 @@ bool encode_png_bytes(const wxImage &image, std::vector<unsigned char> &out, std
                                   : encode_gray_png_bytes(image, out, error);
 }
 
-// A wxImage over decoded pixels, so the encoders above can be reached from an in-memory image as well as
-// from a file. Grayscale is expanded to the three equal channels wxImage always stores, which is what
-// image_has_color() then reads as "no colour" - so a grey image still encodes as a grayscale PNG.
-//
-// `scratch` holds the pixel buffer: the wxImage is constructed over it without taking ownership, so it
-// has to outlive every use of the returned image.
-wxImage image_from_decoded(const DecodedHeightTexture &image, std::vector<unsigned char> &scratch)
-{
-    if (image.empty())
-        return wxImage();
-
-    const size_t n = size_t(image.width) * size_t(image.height);
-    scratch.resize(n * 3);
-    if (image.has_color())
-        scratch.assign(image.rgb.begin(), image.rgb.end());
-    else
-        for (size_t i = 0; i < n; ++i)
-            scratch[i * 3] = scratch[i * 3 + 1] = scratch[i * 3 + 2] = image.pixels[i];
-
-    return wxImage(image.width, image.height, scratch.data(), /* static_data */ true);
-}
-
 std::vector<unsigned char> read_file_bytes(const std::string &path)
 {
     std::ifstream ifs(path, std::ios::binary);
@@ -209,42 +186,6 @@ bool is_supported_height_map(const std::vector<unsigned char> &bytes)
 std::vector<TextureLibraryEntry> g_library;
 bool                             g_library_scanned = false;
 
-// Writes `bytes` into the user's own texture folder as `stem`.png, uniquified so an existing texture -
-// shipped-name collision, or a second edit of the same source - is never overwritten. Returns the new
-// file's library entry. Shared by import_texture_to_library() and save_texture_to_library(), which
-// differ only in where their bytes came from.
-std::optional<TextureLibraryEntry> write_user_texture(const std::vector<unsigned char> &bytes, const std::string &stem,
-                                                      std::string &error)
-{
-    const std::string user_dir = user_texture_dir();
-    if (user_dir.empty()) {
-        error = _u8L("Could not create the folder for imported textures.");
-        return std::nullopt;
-    }
-
-    boost::filesystem::path dest = boost::filesystem::path(user_dir) / (stem + ".png");
-    for (int i = 2; boost::filesystem::exists(dest); ++i)
-        dest = boost::filesystem::path(user_dir) / (stem + " (" + std::to_string(i) + ").png");
-
-    {
-        boost::nowide::ofstream ofs(dest.string(), std::ios::binary);
-        ofs.write(reinterpret_cast<const char *>(bytes.data()), std::streamsize(bytes.size()));
-        if (!ofs.good()) {
-            error = _u8L("Failed to save the imported texture.");
-            return std::nullopt;
-        }
-    }
-
-    texture_library(true); // pick the new file up
-    const std::string dest_str = dest.string();
-    for (const TextureLibraryEntry &e : g_library)
-        if (e.path == dest_str)
-            return e;
-
-    error = _u8L("Failed to save the imported texture.");
-    return std::nullopt;
-}
-
 // The user's own textures, most recently used first, kept in the app config. File names are stored rather
 // than paths so the order survives a moved data directory; '/' separates them because no platform allows
 // it inside a file name. Bounded so a long-lived config does not grow a line without end.
@@ -376,6 +317,12 @@ bool remove_user_texture(const std::string &path, std::string &error)
 
 std::optional<TextureLibraryEntry> import_texture_to_library(const std::string &source_path, std::string &error)
 {
+    const std::string user_dir = user_texture_dir();
+    if (user_dir.empty()) {
+        error = _u8L("Could not create the folder for imported textures.");
+        return std::nullopt;
+    }
+
     wxImage image;
     if (!image.LoadFile(from_u8(source_path)) || !image.IsOk()) {
         error = _u8L("Could not load the selected image.");
@@ -386,7 +333,30 @@ std::optional<TextureLibraryEntry> import_texture_to_library(const std::string &
     if (!encode_png_bytes(image, bytes, error))
         return std::nullopt;
 
-    return write_user_texture(bytes, boost::filesystem::path(source_path).stem().string(), error);
+    // Never overwrite an existing texture (the user's or, if they picked the same name twice, their
+    // own earlier import) - uniquify instead.
+    const std::string       stem = boost::filesystem::path(source_path).stem().string();
+    boost::filesystem::path dest = boost::filesystem::path(user_dir) / (stem + ".png");
+    for (int i = 2; boost::filesystem::exists(dest); ++i)
+        dest = boost::filesystem::path(user_dir) / (stem + " (" + std::to_string(i) + ").png");
+
+    {
+        boost::nowide::ofstream ofs(dest.string(), std::ios::binary);
+        ofs.write(reinterpret_cast<const char *>(bytes.data()), std::streamsize(bytes.size()));
+        if (!ofs.good()) {
+            error = _u8L("Failed to save the imported texture.");
+            return std::nullopt;
+        }
+    }
+
+    texture_library(true); // pick the new file up
+    const std::string dest_str = dest.string();
+    for (const TextureLibraryEntry &e : g_library)
+        if (e.path == dest_str)
+            return e;
+
+    error = _u8L("Failed to save the imported texture.");
+    return std::nullopt;
 }
 
 std::shared_ptr<std::vector<unsigned char>> load_texture_image_data(const std::string &path, std::string &error)
@@ -412,21 +382,4 @@ std::shared_ptr<std::vector<unsigned char>> load_texture_image_data(const std::s
     return std::make_shared<std::vector<unsigned char>>(std::move(converted));
 }
 
-std::optional<TextureLibraryEntry> save_texture_to_library(const DecodedHeightTexture &image, const std::string &stem,
-                                                           std::string &error)
-{
-    std::vector<unsigned char> scratch;
-    const wxImage              wx = image_from_decoded(image, scratch);
-    if (!wx.IsOk()) {
-        error = _u8L("The selected image is empty.");
-        return std::nullopt;
-    }
-
-    std::vector<unsigned char> bytes;
-    if (!encode_png_bytes(wx, bytes, error))
-        return std::nullopt;
-
-    return write_user_texture(bytes, stem.empty() ? std::string("texture") : stem, error);
-}
-
 } // namespace Slic3r::GUI

src/slic3r/GUI/TextureLibrary.hpp

@@ -6,8 +6,6 @@
 #include <string>
 #include <vector>
 
-#include "libslic3r/TextureDisplacement.hpp"
-
 namespace Slic3r::GUI {
 
 // One selectable height-map texture in the texture-displacement gizmo's texture picker.
@@ -59,14 +57,6 @@ std::optional<TextureLibraryEntry> import_texture_to_library(const std::string &
 // Returns nullptr with `error` set if the file cannot be read or decoded at all.
 std::shared_ptr<std::vector<unsigned char>> load_texture_image_data(const std::string &path, std::string &error);
 
-// Writes `image` into user_texture_dir() as a new PNG named after `stem` (uniquified if taken, so an
-// existing texture is never overwritten) and returns its library entry. The in-memory counterpart of
-// import_texture_to_library(), for an image that was edited rather than read off disk.
-//
-// Returns nullopt with `error` set on failure.
-std::optional<TextureLibraryEntry> save_texture_to_library(const DecodedHeightTexture &image, const std::string &stem,
-                                                           std::string &error);
-
 } // namespace Slic3r::GUI
 
 #endif // slic3r_TextureLibrary_hpp_

tests/libslic3r/test_texture_displacement.cpp

@@ -28,7 +28,6 @@
 
 #include <algorithm>
 #include <array>
-#include <functional>
 #include <cmath>
 #include <fstream>
 #include <limits>
@@ -2176,290 +2175,352 @@ TEST_CASE("whether a layer's texture has colour agrees with its decode", "[Textu
     CHECK_FALSE(height_texture_has_color(TextureDisplacementLayer{}));
 }
 
-// ---- Image adjustments (the gizmo's image-adjustment panel) ----------------------------------------
+// ---------------------------------------------------------------------------------------------
+// The model's own UV channel, and the Override blend mode
+// ---------------------------------------------------------------------------------------------
 
-// A grayscale ramp 0..255 across the width, so every input level is present exactly once per row and a
-// tonal curve can be read straight off the output.
-static DecodedHeightTexture make_gray_ramp(int w = 256, int h = 4)
+// A grayscale image that is black in its left half and white in its right half, so where a sample
+// lands along u is readable straight off the height it comes back with.
+static std::shared_ptr<std::vector<unsigned char>> make_left_right_split_png(size_t w = 16, size_t h = 16)
 {
-    DecodedHeightTexture t;
-    t.width  = w;
-    t.height = h;
-    t.pixels.resize(size_t(w) * size_t(h));
-    for (int y = 0; y < h; ++y)
-        for (int x = 0; x < w; ++x)
-            t.pixels[size_t(y) * size_t(w) + size_t(x)] = uint8_t(x * 255 / std::max(1, w - 1));
-    return t;
-}
+    std::vector<uint8_t> pixels(w * h);
+    for (size_t y = 0; y < h; ++y)
+        for (size_t x = 0; x < w; ++x)
+            pixels[y * w + x] = (x < w / 2) ? 0 : 255;
+    const boost::filesystem::path tmp_path = boost::filesystem::temp_directory_path()
+        / boost::filesystem::unique_path("texdisp_test_%%%%%%%%.png");
+    REQUIRE(Slic3r::png::write_gray_to_file(tmp_path.string(), w, h, pixels));
 
-// A one-texel checkerboard of 0 and 255 - the highest spatial frequency the grid can hold, which is what
-// a blur has to remove and a downscale has to average rather than drop.
-static DecodedHeightTexture make_gray_checkerboard(int w = 16, int h = 16)
-{
-    DecodedHeightTexture t;
-    t.width  = w;
-    t.height = h;
-    t.pixels.resize(size_t(w) * size_t(h));
-    for (int y = 0; y < h; ++y)
-        for (int x = 0; x < w; ++x)
-            t.pixels[size_t(y) * size_t(w) + size_t(x)] = ((x + y) % 2 == 0) ? 0 : 255;
-    return t;
-}
-
-static DecodedHeightTexture make_rgb_flat(uint8_t r, uint8_t g, uint8_t b, int w = 8, int h = 8)
-{
-    DecodedHeightTexture t;
-    t.width  = w;
-    t.height = h;
-    t.pixels.resize(size_t(w) * size_t(h));
-    t.rgb.resize(size_t(w) * size_t(h) * 3);
-    for (size_t i = 0; i < size_t(w) * size_t(h); ++i) {
-        t.rgb[i * 3]     = r;
-        t.rgb[i * 3 + 1] = g;
-        t.rgb[i * 3 + 2] = b;
-        t.pixels[i]      = uint8_t(std::lround(0.299 * r + 0.587 * g + 0.114 * b));
+    std::vector<unsigned char> bytes;
+    {
+        std::ifstream ifs(tmp_path.string(), std::ios::binary);
+        bytes.assign(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());
     }
-    return t;
+    boost::system::error_code ec;
+    boost::filesystem::remove(tmp_path, ec);
+
+    REQUIRE_FALSE(bytes.empty());
+    return std::make_shared<std::vector<unsigned char>>(std::move(bytes));
 }
 
-TEST_CASE("an adjustment that moves no slider returns the image unchanged", "[TextureDisplacement]")
+// Where a sheet coordinate lands in uv: across [UV_LO, UV_LO + UV_SPAN] rather than the full [0, 1].
+// The inset keeps the tests off the exact edge of an untiled placement, where there is deliberately no
+// texture at all rather than its border texel (see DecodedHeightTexture::sample()) - a real model's
+// channel does reach 1.0, and a vertex sitting exactly there displaces by nothing on purpose.
+static constexpr float UV_LO   = 0.1f;
+static constexpr float UV_SPAN = 0.8f;
+
+static float sheet_uv_at(float coord, float size, bool mirror = false)
 {
-    const DecodedHeightTexture src = make_gray_ramp();
-    const DecodedHeightTexture out = apply_texture_adjustments(src, TextureAdjustments{});
-    CHECK(out.width == src.width);
-    CHECK(out.height == src.height);
-    CHECK(out.pixels == src.pixels);
-    CHECK(TextureAdjustments{}.identity());
+    const float t = coord / size;
+    return UV_LO + UV_SPAN * (mirror ? 1.f - t : t);
 }
 
-TEST_CASE("brightness reaches pure white and pure black only at the ends of its range", "[TextureDisplacement]")
+// One UV per triangle corner: u follows x, v follows y. `mirror_u` mirrors u, which is what the tests
+// use to show the bake is really reading the channel rather than projecting the position.
+static std::vector<Vec2f> sheet_uv_channel(const indexed_triangle_set &sheet, float size, bool mirror_u = false)
 {
-    const DecodedHeightTexture src = make_gray_ramp();
-
-    TextureAdjustments up;
-    up.brightness = 1.f;
-    const DecodedHeightTexture white = apply_texture_adjustments(src, up);
-    CHECK(std::all_of(white.pixels.begin(), white.pixels.end(), [](uint8_t v) { return v == 255; }));
-
-    TextureAdjustments down;
-    down.brightness = -1.f;
-    const DecodedHeightTexture black = apply_texture_adjustments(src, down);
-    CHECK(std::all_of(black.pixels.begin(), black.pixels.end(), [](uint8_t v) { return v == 0; }));
+    std::vector<Vec2f> uv(sheet.indices.size() * 3);
+    for (size_t f = 0; f < sheet.indices.size(); ++f)
+        for (int k = 0; k < 3; ++k) {
+            const Vec3f &p = sheet.vertices[size_t(sheet.indices[f][k])];
+            uv[f * 3 + size_t(k)] = Vec2f(sheet_uv_at(p.x(), size, mirror_u), sheet_uv_at(p.y(), size));
+        }
+    return uv;
 }
 
-TEST_CASE("brightness lifts the image without flattening it into a clipped plateau", "[TextureDisplacement]")
-{
-    // The reason brightness is a lift toward white rather than an additive offset: an offset would drive
-    // everything above mid-grey to a flat 255, and since this image is also the height map that region
-    // would bake as flat relief. Half a stop up must leave almost nothing at pure white.
-    const DecodedHeightTexture src = make_gray_ramp();
-    TextureAdjustments         adj;
-    adj.brightness = 0.5f;
-    const DecodedHeightTexture out = apply_texture_adjustments(src, adj);
-
-    REQUIRE(out.pixels.size() == src.pixels.size());
-    const size_t clipped = size_t(std::count(out.pixels.begin(), out.pixels.end(), uint8_t(255)));
-    CHECK(clipped * 100 < out.pixels.size()); // under 1%; an additive shift would clip half the ramp
-
-    // Every texel got brighter, and the curve stays ordered: brighter in means brighter out.
-    for (size_t i = 0; i < out.pixels.size(); ++i)
-        REQUIRE(out.pixels[i] >= src.pixels[i]);
-    for (int x = 1; x < out.width; ++x)
-        REQUIRE(out.pixels[size_t(x)] >= out.pixels[size_t(x - 1)]);
-}
-
-TEST_CASE("contrast at its lowest flattens the image to mid-grey and at its highest spreads it apart",
+TEST_CASE("Override blend replaces the displacement under it instead of combining with it",
           "[TextureDisplacement]")
 {
-    const DecodedHeightTexture src = make_gray_ramp();
-
-    TextureAdjustments flat;
-    flat.contrast = -1.f;
-    const DecodedHeightTexture grey = apply_texture_adjustments(src, flat);
-    // One value everywhere - the pivot. Which exact level that rounds to is not the point.
-    CHECK(std::adjacent_find(grey.pixels.begin(), grey.pixels.end(), std::not_equal_to<uint8_t>()) ==
-          grey.pixels.end());
-
-    TextureAdjustments hard;
-    hard.contrast = 1.f;
-    const DecodedHeightTexture split = apply_texture_adjustments(src, hard);
-    // A threshold about the pivot: the dark end of the ramp goes to black, the light end to white.
-    CHECK(split.pixels[0] == 0);
-    CHECK(split.pixels[size_t(split.width - 1)] == 255);
+    CHECK_THAT(blend_displacement(3.f, 1.f, TextureBlendMode::Override), WithinAbs(1.f, 1e-6f));
+    // Nothing underneath yet is still just the value, so an Override layer at the bottom of the
+    // stack behaves exactly like the Add the bake forces there.
+    CHECK_THAT(blend_displacement(0.f, 1.f, TextureBlendMode::Override), WithinAbs(1.f, 1e-6f));
+    // The sign carries, and a zero sample really does flatten what is under it - that is the point.
+    CHECK_THAT(blend_displacement(3.f, -1.f, TextureBlendMode::Override), WithinAbs(-1.f, 1e-6f));
+    CHECK_THAT(blend_displacement(3.f, 0.f, TextureBlendMode::Override), WithinAbs(0.f, 1e-6f));
 }
 
-TEST_CASE("blur removes the finest detail and sharpness exaggerates an edge", "[TextureDisplacement]")
+TEST_CASE("an Override layer leaves only its own relief where two layers overlap", "[TextureDisplacement]")
 {
-    // Blur: a one-texel checkerboard is the highest frequency the grid holds, so a blur has to collapse it
-    // toward its own mean. Measured as mean absolute deviation, which needs no assumption about the mean.
-    const DecodedHeightTexture checker = make_gray_checkerboard(32, 32);
-    const auto                 deviation = [](const DecodedHeightTexture &t) {
-        double mean = 0.;
-        for (uint8_t v : t.pixels)
-            mean += double(v);
-        mean /= double(t.pixels.size());
-        double dev = 0.;
-        for (uint8_t v : t.pixels)
-            dev += std::abs(double(v) - mean);
-        return dev / double(t.pixels.size());
-    };
-    TextureAdjustments blur;
-    blur.blur = 1.f;
-    CHECK(deviation(apply_texture_adjustments(checker, blur)) < 0.25 * deviation(checker));
+    const indexed_triangle_set cube = its_make_cube(10., 10., 10.);
 
-    // Sharpness: an unsharp mask pushes each side of a step further from the other, so the step
-    // overshoots - darker than the dark side just inside it, brighter than the bright side just inside.
-    DecodedHeightTexture step;
-    step.width  = 64;
-    step.height = 8;
-    step.pixels.assign(size_t(step.width) * size_t(step.height), 100);
-    for (int y = 0; y < step.height; ++y)
-        for (int x = step.width / 2; x < step.width; ++x)
-            step.pixels[size_t(y) * size_t(step.width) + size_t(x)] = 150;
+    TextureDisplacementLayer base;
+    base.slot         = 0;
+    base.depth_mm     = 2.0f;
+    base.tiling_scale = 5.0f;
+    base.image_data   = make_flat_gray_png(255); // full depth everywhere
 
-    TextureAdjustments sharp;
-    sharp.sharpness = 1.f;
-    const DecodedHeightTexture sharpened = apply_texture_adjustments(step, sharp);
-    const size_t               row       = size_t(step.height / 2) * size_t(step.width);
-    const size_t               mid       = size_t(step.width / 2);
-    CHECK(sharpened.pixels[row + mid - 1] < 100); // undershoot on the dark side of the step
-    CHECK(sharpened.pixels[row + mid] > 150);     // overshoot on the light side
-}
+    TextureDisplacementLayer second = base;
+    second.slot       = 1;
+    second.depth_mm   = 0.5f;
+    second.blend_mode = TextureBlendMode::Override;
 
-TEST_CASE("a grayscale image stays grayscale and its hue slider does nothing", "[TextureDisplacement]")
-{
-    const DecodedHeightTexture src = make_gray_ramp();
-    REQUIRE_FALSE(src.has_color());
+    TextureDisplacementFacetsData facets{};
+    facets[0] = paint_whole_mesh(cube);
+    facets[1] = facets[0];
 
-    TextureAdjustments hue;
-    hue.hue_deg = 120.f;
-    const DecodedHeightTexture out = apply_texture_adjustments(src, hue);
-    // Not promoted to RGB: a grey image has no colour to offer the layer's colour feature, and storing it
-    // as RGB would triple the PNG for a row of identical greys.
-    CHECK_FALSE(out.has_color());
-    CHECK(out.rgb.empty());
-    CHECK(out.pixels == src.pixels);
-}
+    const indexed_triangle_set overridden = build_texture_displacement(cube, {base, second}, facets, classic_options());
+    REQUIRE(overridden.vertices.size() == cube.vertices.size());
 
-TEST_CASE("a colour image's height stays the luminance of its adjusted colour", "[TextureDisplacement]")
-{
-    // The invariant that keeps the relief and the colour from drifting apart: whatever the adjustment did
-    // to the channels, the height is recomputed from the channels that came out.
-    const DecodedHeightTexture src = make_rgb_flat(200, 60, 30);
-    REQUIRE(src.has_color());
+    // Add would have piled the two up to 2.5 mm; Override keeps the upper layer's 0.5 mm alone.
+    TextureDisplacementLayer added = second;
+    added.blend_mode               = TextureBlendMode::Add;
+    const indexed_triangle_set summed = build_texture_displacement(cube, {base, added}, facets, classic_options());
+    REQUIRE(summed.vertices.size() == cube.vertices.size());
 
-    TextureAdjustments adj;
-    adj.brightness = 0.2f;
-    adj.contrast   = 0.3f;
-    adj.hue_deg    = 75.f;
-    const DecodedHeightTexture out = apply_texture_adjustments(src, adj);
-    REQUIRE(out.has_color());
-
-    for (size_t i = 0; i < out.pixels.size(); ++i) {
-        const long expect = std::lround(0.299 * out.rgb[i * 3] + 0.587 * out.rgb[i * 3 + 1] +
-                                        0.114 * out.rgb[i * 3 + 2]);
-        REQUIRE(long(out.pixels[i]) == expect);
+    for (size_t i = 0; i < cube.vertices.size(); ++i) {
+        if (!above_resting_plane(cube, i))
+            continue;
+        CHECK_THAT((overridden.vertices[i] - cube.vertices[i]).norm(), WithinAbs(0.5f, 1e-3f));
+        CHECK_THAT((summed.vertices[i] - cube.vertices[i]).norm(), WithinAbs(2.5f, 1e-3f));
     }
-    // The hue turn actually moved the colour, so the check above is not passing on an unchanged image.
-    CHECK(out.rgb != src.rgb);
 }
 
-TEST_CASE("a full turn of the hue leaves a colour where it started", "[TextureDisplacement]")
+TEST_CASE("the ModelUV mapping displaces through the model's own UV channel", "[TextureDisplacement]")
 {
-    const DecodedHeightTexture src = make_rgb_flat(200, 60, 30);
-    TextureAdjustments         adj;
-    adj.hue_deg                    = 360.f;
-    const DecodedHeightTexture out = apply_texture_adjustments(src, adj);
-    REQUIRE(out.has_color());
-    // Rounding through 8-bit channels, so a level or two of slack rather than exact equality.
-    for (size_t i = 0; i < out.rgb.size(); ++i)
-        REQUIRE(std::abs(int(out.rgb[i]) - int(src.rgb[i])) <= 2);
+    constexpr float            size  = 10.f;
+    const indexed_triangle_set sheet = make_flat_sheet(size, 1.f);
+
+    TextureDisplacementLayer layer;
+    layer.slot         = 0;
+    layer.depth_mm     = 1.0f;
+    layer.image_data   = make_left_right_split_png();
+    layer.tile_enabled = false; // the layout is the placement; nothing should repeat
+    layer.projection_method = TextureProjectionMethod::ModelUV;
+
+    TextureDisplacementFacetsData facets{};
+    facets[0] = paint_whole_mesh(sheet);
+
+    const std::vector<Vec2f> uv      = sheet_uv_channel(sheet, size);
+    const std::vector<Vec2f> flipped = sheet_uv_channel(sheet, size, /* mirror_u */ true);
+
+    const indexed_triangle_set out = build_texture_displacement(sheet, {layer}, facets, classic_options(), {}, nullptr,
+                                                                 Transform3d::Identity(), nullptr, nullptr, &uv);
+    REQUIRE(out.vertices.size() == sheet.vertices.size());
+
+    // The image is black for u < 0.5 and white above it, and the channel's u rises with x across the
+    // sheet, so it comes out flat on its left half and raised by the full depth on its right.
+    size_t low = 0, high = 0;
+    for (size_t i = 0; i < sheet.vertices.size(); ++i) {
+        const float x    = sheet.vertices[i].x();
+        const float dz   = out.vertices[i].z() - sheet.vertices[i].z();
+        if (x < 0.4f * size) {
+            CHECK_THAT(dz, WithinAbs(0.f, 1e-3f));
+            ++low;
+        } else if (x > 0.6f * size) {
+            CHECK_THAT(dz, WithinAbs(layer.depth_mm, 1e-3f));
+            ++high;
+        }
+    }
+    REQUIRE(low > 0);
+    REQUIRE(high > 0);
+
+    // Mirroring the channel mirrors the relief: the mapping really is the channel's, not a planar
+    // projection of the position (which would be unchanged by it).
+    const indexed_triangle_set mirrored = build_texture_displacement(sheet, {layer}, facets, classic_options(), {},
+                                                                      nullptr, Transform3d::Identity(), nullptr, nullptr,
+                                                                      &flipped);
+    REQUIRE(mirrored.vertices.size() == sheet.vertices.size());
+    for (size_t i = 0; i < sheet.vertices.size(); ++i) {
+        const float x = sheet.vertices[i].x();
+        if (x < 0.4f * size)
+            CHECK_THAT(mirrored.vertices[i].z() - sheet.vertices[i].z(), WithinAbs(layer.depth_mm, 1e-3f));
+        else if (x > 0.6f * size)
+            CHECK_THAT(mirrored.vertices[i].z() - sheet.vertices[i].z(), WithinAbs(0.f, 1e-3f));
+    }
 }
 
-TEST_CASE("the adjustment blur radius ramps from zero and stays under its cost cap", "[TextureDisplacement]")
-{
-    CHECK_THAT(adjustment_blur_radius(0.f, 512, 512), Catch::Matchers::WithinAbs(0.f, 1e-6f));
-    // 5% of the short side, as the Smoothing slider uses.
-    CHECK_THAT(adjustment_blur_radius(1.f, 512, 512), Catch::Matchers::WithinAbs(25.6f, 1e-3f));
-    CHECK_THAT(adjustment_blur_radius(0.5f, 512, 512), Catch::Matchers::WithinAbs(12.8f, 1e-3f));
-    // Capped, so a large image at the top of the slider cannot cost without bound.
-    CHECK_THAT(adjustment_blur_radius(1.f, 8192, 8192), Catch::Matchers::WithinAbs(48.f, 1e-3f));
-    // Sized off the short side, not the long one.
-    CHECK_THAT(adjustment_blur_radius(1.f, 4096, 200), Catch::Matchers::WithinAbs(10.f, 1e-3f));
-}
-
-TEST_CASE("downscaling a height texture averages the texels it drops and never upscales",
+TEST_CASE("a ModelUV layer falls back to Triplanar when the volume carries no UV channel",
           "[TextureDisplacement]")
 {
-    // Averaging, not decimation: a one-texel checkerboard halved must come out uniformly mid-grey. Picking
-    // one texel per block would instead come out all black or all white - detail the adjustment never
-    // produced, shown in the preview.
-    const DecodedHeightTexture small = downscale_height_texture(make_gray_checkerboard(16, 16), 8);
-    CHECK(small.width == 8);
-    CHECK(small.height == 8);
-    CHECK(std::all_of(small.pixels.begin(), small.pixels.end(), [](uint8_t v) { return v == 127; }));
+    constexpr float            size  = 10.f;
+    const indexed_triangle_set sheet = make_flat_sheet(size, 2.f);
 
-    // Already within the limit: handed back as it is.
-    const DecodedHeightTexture ramp = make_gray_ramp(64, 4);
-    const DecodedHeightTexture same = downscale_height_texture(ramp, 256);
-    CHECK(same.width == ramp.width);
-    CHECK(same.height == ramp.height);
-    CHECK(same.pixels == ramp.pixels);
-
-    // Aspect preserved, and a colour source keeps its colour.
-    const DecodedHeightTexture wide = downscale_height_texture(make_rgb_flat(200, 60, 30, 400, 100), 100);
-    CHECK(wide.width == 100);
-    CHECK(wide.height == 25);
-    CHECK(wide.has_color());
-}
-
-TEST_CASE("a layer's live image adjustment reaches its decode", "[TextureDisplacement]")
-{
-    // This is what makes the image-adjustment panel's sliders move the relief: decode_height_texture()
-    // applies the layer's preview_adjust, so everything downstream of the decode - the displacement, the
-    // colour, the thumbnails, the bake - sees the adjusted image without being told about the panel.
     TextureDisplacementLayer layer;
-    layer.image_data = make_checkerboard_png(32, 32);
+    layer.slot         = 0;
+    layer.depth_mm     = 1.0f;
+    layer.tiling_scale = 5.0f;
+    layer.image_data   = make_flat_gray_png(255);
 
-    const DecodedHeightTexture raw = decode_height_texture(layer);
-    REQUIRE_FALSE(raw.empty());
+    TextureDisplacementFacetsData facets{};
+    facets[0] = paint_whole_mesh(sheet);
 
-    // An untouched panel, and a closed one, cost nothing and change nothing.
-    layer.preview_adjust = TextureAdjustments{};
-    CHECK(decode_height_texture(layer).pixels == raw.pixels);
+    layer.projection_method                 = TextureProjectionMethod::Triplanar;
+    const indexed_triangle_set as_triplanar = build_texture_displacement(sheet, {layer}, facets, classic_options());
+    layer.projection_method                 = TextureProjectionMethod::ModelUV;
+    const indexed_triangle_set no_channel    = build_texture_displacement(sheet, {layer}, facets, classic_options());
 
-    layer.preview_adjust.brightness = 0.5f;
-    const DecodedHeightTexture bright = decode_height_texture(layer);
-    CHECK(bright.pixels != raw.pixels);
-    CHECK(bright.pixels == apply_texture_adjustments(raw, layer.preview_adjust).pixels);
-
-    // Back to identity gives the stored image back, so closing the panel really does revert the layer.
-    layer.preview_adjust = TextureAdjustments{};
-    CHECK(decode_height_texture(layer).pixels == raw.pixels);
+    REQUIRE(no_channel.vertices.size() == as_triplanar.vertices.size());
+    for (size_t i = 0; i < as_triplanar.vertices.size(); ++i)
+        CHECK_THAT((no_channel.vertices[i] - as_triplanar.vertices[i]).norm(), WithinAbs(0.f, 1e-5f));
 }
 
-TEST_CASE("changing a live adjustment is not served the previous one from cache", "[TextureDisplacement]")
+TEST_CASE("a bake with colour off on every layer reports no colour at all", "[TextureDisplacement]")
 {
-    // The decode caches by the image_data pointer, which does not change while a slider moves - so the
-    // adjustment has to be part of the key or every slider move past the first would redraw the same
-    // pixels. Same for the smoothed copy, which is computed on top of the adjusted one.
+    const indexed_triangle_set cube = its_make_cube(10., 10., 10.);
+
     TextureDisplacementLayer layer;
-    layer.image_data = make_checkerboard_png(32, 32);
-    const DecodedHeightTexture raw = decode_height_texture(layer);
-    REQUIRE_FALSE(raw.empty());
+    layer.slot          = 0;
+    layer.depth_mm      = 1.0f;
+    layer.tiling_scale  = 5.0f;
+    layer.image_data    = make_flat_rgb_png(200, 40, 10); // has colour to give...
+    layer.color_enabled = false;                          // ...but is not asked for it
 
-    layer.preview_adjust.brightness = 0.5f;
-    const std::vector<uint8_t> bright = decode_height_texture(layer).pixels;
-    layer.preview_adjust.brightness   = -0.5f;
-    const std::vector<uint8_t> dark   = decode_height_texture(layer).pixels;
-    CHECK(bright != dark);
-    CHECK(dark == apply_texture_adjustments(raw, layer.preview_adjust).pixels);
+    TextureDisplacementFacetsData facets{};
+    facets[0] = paint_whole_mesh(cube);
 
-    // The same question again with smoothing on, which is cached separately and keyed by both.
-    layer.smoothing                 = 0.5f;
-    layer.preview_adjust.brightness = 0.5f;
-    const std::vector<uint8_t> smooth_bright = decode_height_texture(layer).pixels;
-    layer.preview_adjust.brightness          = -0.5f;
-    const std::vector<uint8_t> smooth_dark   = decode_height_texture(layer).pixels;
-    CHECK(smooth_bright != smooth_dark);
+    std::vector<uint8_t> triangle_color;
+    TextureColorRequest  request;
+    request.quantize     = [](const Vec3f &) { return 0; }; // would colour everything, if asked
+    request.out_triangle = &triangle_color;
+
+    const indexed_triangle_set out = build_texture_displacement(cube, {layer}, facets, classic_options(), {}, &request);
+    REQUIRE_FALSE(out.vertices.empty());
+    // Every entry 0 ("this triangle takes no colour from the texture"), so the commit leaves whatever
+    // the model was already painted with exactly as it was.
+    for (const uint8_t entry : triangle_color)
+        CHECK(entry == 0);
+}
+
+TEST_CASE("transfer_uv_channel resamples a UV channel onto a subdivided copy of the same surface",
+          "[TextureDisplacement]")
+{
+    constexpr float            size   = 10.f;
+    const indexed_triangle_set coarse = make_flat_sheet(size, 5.f);
+    const indexed_triangle_set fine   = make_flat_sheet(size, 1.f);
+    const std::vector<Vec2f>   uv     = sheet_uv_channel(coarse, size);
+
+    const std::vector<Vec2f> moved = transfer_uv_channel(coarse, uv, fine);
+    REQUIRE(moved.size() == fine.indices.size() * 3);
+
+    // The channel is affine in position here (u = x/size, v = y/size), so a correct transfer
+    // reproduces it exactly at every corner of the finer mesh.
+    for (size_t f = 0; f < fine.indices.size(); ++f)
+        for (int k = 0; k < 3; ++k) {
+            const Vec3f &p = fine.vertices[size_t(fine.indices[f][k])];
+            CHECK_THAT(moved[f * 3 + size_t(k)].x(), WithinAbs(sheet_uv_at(p.x(), size), 1e-4f));
+            CHECK_THAT(moved[f * 3 + size_t(k)].y(), WithinAbs(sheet_uv_at(p.y(), size), 1e-4f));
+        }
+
+    // A mismatched channel is refused rather than read past its end.
+    CHECK(transfer_uv_channel(coarse, {Vec2f::Zero()}, fine).empty());
+    CHECK(transfer_uv_channel(coarse, uv, indexed_triangle_set{}).empty());
+}
+
+TEST_CASE("the model's per-corner UVs survive a brush split and collapse to one per vertex",
+          "[TextureDisplacement]")
+{
+    constexpr float            size  = 10.f;
+    const indexed_triangle_set sheet = make_flat_sheet(size, 5.f);
+    const std::vector<Vec2f>   uv    = sheet_uv_channel(sheet, size);
+
+    // The whole sheet as a patch, with the source map the channel is read through.
+    const TriangleMesh tm(sheet);
+    TriangleSelector   selector(tm);
+    for (int f = 0; f < int(sheet.indices.size()); ++f)
+        selector.set_facet(f, EnforcerBlockerType::ENFORCER);
+    std::vector<int>           source;
+    const indexed_triangle_set patch = selector.get_facets_strict(EnforcerBlockerType::ENFORCER, &source);
+    REQUIRE(patch.indices.size() == source.size());
+
+    const std::vector<Vec2f> corner = compute_model_corner_uvs(sheet, uv, patch, source);
+    REQUIRE(corner.size() == patch.indices.size() * 3);
+    // An unsplit patch triangle *is* its source triangle, so its corners reproduce the channel.
+    for (size_t f = 0; f < patch.indices.size(); ++f)
+        for (int k = 0; k < 3; ++k) {
+            const Vec3f &p = patch.vertices[size_t(patch.indices[f][k])];
+            CHECK_THAT(corner[f * 3 + size_t(k)].x(), WithinAbs(sheet_uv_at(p.x(), size), 1e-4f));
+            CHECK_THAT(corner[f * 3 + size_t(k)].y(), WithinAbs(sheet_uv_at(p.y(), size), 1e-4f));
+        }
+
+    const std::vector<Vec2f> per_vertex = collapse_corner_uvs(patch, corner);
+    REQUIRE(per_vertex.size() == patch.vertices.size());
+    for (size_t i = 0; i < patch.vertices.size(); ++i) {
+        CHECK_THAT(per_vertex[i].x(), WithinAbs(sheet_uv_at(patch.vertices[i].x(), size), 1e-4f));
+        CHECK_THAT(per_vertex[i].y(), WithinAbs(sheet_uv_at(patch.vertices[i].y(), size), 1e-4f));
+    }
+
+    // Mismatched inputs report nothing rather than guessing.
+    CHECK(compute_model_corner_uvs(sheet, {Vec2f::Zero()}, patch, source).empty());
+    CHECK(compute_model_corner_uvs(sheet, uv, patch, {}).empty());
+    CHECK(collapse_corner_uvs(patch, {Vec2f::Zero()}).empty());
+}
+
+TEST_CASE("facet paint is carried onto a rebuilt mesh by each facet's foot point", "[TextureDisplacement]")
+{
+    constexpr float            size   = 10.f;
+    const indexed_triangle_set coarse = make_flat_sheet(size, 2.5f);
+
+    // Two filaments, split down the middle - the pattern the transfer has to reproduce.
+    const TriangleMesh coarse_mesh(coarse);
+    TriangleSelector   painter(coarse_mesh);
+    for (size_t t = 0; t < coarse.indices.size(); ++t) {
+        const stl_triangle_vertex_indices &tri = coarse.indices[t];
+        const float x = (coarse.vertices[size_t(tri[0])].x() + coarse.vertices[size_t(tri[1])].x() +
+                         coarse.vertices[size_t(tri[2])].x()) / 3.f;
+        painter.set_facet(int(t), x < 0.5f * size ? EnforcerBlockerType::Extruder1 : EnforcerBlockerType::Extruder2);
+    }
+    const TriangleSelector::TriangleSplittingData paint = painter.serialize();
+
+    // A finer mesh, lifted clear of the original surface the way a bake's relief lifts it. This is
+    // what ModelVolume::restore_painting()'s 0.01 mm overlap remap cannot follow.
+    indexed_triangle_set lifted = make_flat_sheet(size, 1.f);
+    for (Vec3f &v : lifted.vertices)
+        v.z() += 0.5f;
+
+    const std::vector<uint8_t> state = transfer_facet_paint(coarse, paint, lifted);
+    REQUIRE(state.size() == lifted.indices.size());
+
+    size_t left = 0, right = 0;
+    for (size_t t = 0; t < lifted.indices.size(); ++t) {
+        const stl_triangle_vertex_indices &tri = lifted.indices[t];
+        const float x = (lifted.vertices[size_t(tri[0])].x() + lifted.vertices[size_t(tri[1])].x() +
+                         lifted.vertices[size_t(tri[2])].x()) / 3.f;
+        // Only away from the split: a facet straddling it may legitimately land on either side.
+        if (x < 0.4f * size) {
+            CHECK(state[t] == uint8_t(EnforcerBlockerType::Extruder1));
+            ++left;
+        } else if (x > 0.6f * size) {
+            CHECK(state[t] == uint8_t(EnforcerBlockerType::Extruder2));
+            ++right;
+        }
+    }
+    REQUIRE(left > 0);
+    REQUIRE(right > 0);
+
+    // An unpainted source has nothing to carry, which is not the same as carrying NONE everywhere:
+    // the caller has to tell those apart to decide between resetting the annotation and writing one.
+    CHECK(transfer_facet_paint(coarse, TriangleSelector::TriangleSplittingData{}, lifted).empty());
+    CHECK(transfer_facet_paint(coarse, paint, indexed_triangle_set{}).empty());
+}
+
+TEST_CASE("an unpainted part of the source carries no paint onto the rebuilt mesh", "[TextureDisplacement]")
+{
+    constexpr float            size   = 10.f;
+    const indexed_triangle_set coarse = make_flat_sheet(size, 2.5f);
+
+    // Only the left half is painted at all; the right half must come back NONE rather than borrowing
+    // the nearest painted colour from across the model.
+    const TriangleMesh coarse_mesh(coarse);
+    TriangleSelector   painter(coarse_mesh);
+    for (size_t t = 0; t < coarse.indices.size(); ++t) {
+        const stl_triangle_vertex_indices &tri = coarse.indices[t];
+        const float x = (coarse.vertices[size_t(tri[0])].x() + coarse.vertices[size_t(tri[1])].x() +
+                         coarse.vertices[size_t(tri[2])].x()) / 3.f;
+        if (x < 0.5f * size)
+            painter.set_facet(int(t), EnforcerBlockerType::Extruder3);
+    }
+
+    const std::vector<uint8_t> state = transfer_facet_paint(coarse, painter.serialize(), coarse);
+    REQUIRE(state.size() == coarse.indices.size());
+    for (size_t t = 0; t < coarse.indices.size(); ++t) {
+        const stl_triangle_vertex_indices &tri = coarse.indices[t];
+        const float x = (coarse.vertices[size_t(tri[0])].x() + coarse.vertices[size_t(tri[1])].x() +
+                         coarse.vertices[size_t(tri[2])].x()) / 3.f;
+        if (x < 0.4f * size)
+            CHECK(state[t] == uint8_t(EnforcerBlockerType::Extruder3));
+        else if (x > 0.6f * size)
+            CHECK(state[t] == uint8_t(EnforcerBlockerType::NONE));
+    }
 }