Save where the panel was left, and recover a texture the archive lacks

The project carried the layer stack but not the user's place in it: a reopened
project landed on slot 0 in Standard, whatever they had been editing. The active
layer and Standard/Pro now live on the volume, next to the rest of its options,
and come back with it. Docked/undocked goes to the application config instead -
it describes the user's window, not the model, so opening someone else's project
must not move their panel.

A layer whose image_data was empty at save time was written with no texture and
came back with none. It now falls back to the file the layer came from, which the
importer put in the user's own texture library, so a project reopened on the same
machine keeps its pixels.

The texture is always stored as .png: the importer converts whatever the user
picked, so the extension was being taken from a name that no longer described the
bytes.

Also adds v2_flip_edges to the cereal field list, which the undo stack was
silently dropping.

src/libslic3r/Format/bbs_3mf.cpp

@@ -21,6 +21,7 @@
 #include "libslic3r/BrimEarsPoint.hpp"
 #include "libslic3r/Config.hpp"
 #include "libslic3r/CustomGCode.hpp"
+#include "libslic3r/TextureDisplacement.hpp"
 #include "libslic3r_version.h"
 
 #include "bbs_3mf.hpp"
@@ -62,6 +63,7 @@
 #include <ostream>
 #include <sstream>
 #include <set>
+#include <iterator>
 #include <memory>
 #include <optional>
 #include <map>
@@ -353,6 +355,13 @@ static constexpr const char* CUSTOM_SUPPORTS_ATTR = "paint_supports";
 static constexpr const char* CUSTOM_FUZZY_SKIN_ATTR  = "paint_fuzzy_skin";
 static constexpr const char* CUSTOM_SEAM_ATTR = "paint_seam";
 static constexpr const char* MMU_SEGMENTATION_ATTR = "paint_color";
+// Texture displacement. One paint mask per layer slot, mirroring paint_color; the layer stack itself is
+// a JSON file in the archive, named by the volume metadata key below (see add_texture_displacement()).
+static constexpr const char* TEXTURE_DISPLACEMENT_ATTRS[Slic3r::TEXTURE_DISPLACEMENT_MAX_LAYERS] = {
+    "paint_texture_0", "paint_texture_1", "paint_texture_2", "paint_texture_3",
+    "paint_texture_4", "paint_texture_5", "paint_texture_6", "paint_texture_7" };
+static constexpr const char* TEXTURE_DISPLACEMENT_KEY = "texture_displacement";
+static constexpr const char* TEXTURE_DISPLACEMENT_DIR = "Metadata/texture_displacement/";
 // BBS
 static constexpr const char* FACE_PROPERTY_ATTR = "face_property";
 
@@ -840,6 +849,8 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
             std::vector<std::string> custom_seam;
             std::vector<std::string> mmu_segmentation;
             std::vector<std::string> fuzzy_skin;
+            // One per texture displacement layer slot, each parallel to `triangles` like the masks above.
+            std::vector<std::string> texture_displacement[TEXTURE_DISPLACEMENT_MAX_LAYERS];
             // BBS
             std::vector<std::string> face_properties;
 
@@ -860,6 +871,8 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
                 custom_seam.clear();
                 mmu_segmentation.clear();
                 fuzzy_skin.clear();
+                for (std::vector<std::string> &slot : texture_displacement)
+                    slot.clear();
             }
         };
 
@@ -1193,6 +1206,11 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
         /*IdToSlaSupportPointsMap m_sla_support_points;
         IdToSlaDrainHolesMap    m_sla_drain_holes;*/
         PathToEmbossShapeFileMap m_path_to_emboss_shape_files;
+        // Texture displacement: every file under Metadata/texture_displacement/, by archive path. Volumes
+        // are built only after the whole archive has been walked, so by the time a volume names its JSON
+        // every file it could refer to is already in here, whatever order the archive happened to be in.
+        std::map<std::string, std::string> m_texture_displacement_files;
+        void _apply_texture_displacement(ModelVolume &volume, const std::string &json_path);
         std::string m_curr_metadata_name;
         std::string m_curr_characters;
         std::string m_name;
@@ -2066,6 +2084,13 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
                 else if (_is_svg_shape_file(name)) {
                     _extract_embossed_svg_shape_file(name, archive, stat);
                 }
+                else if (boost::algorithm::istarts_with(name, TEXTURE_DISPLACEMENT_DIR)) {
+                    std::string contents(stat.m_uncomp_size, '\0');
+                    if (mz_zip_reader_extract_to_mem(&archive, stat.m_file_index, contents.data(), stat.m_uncomp_size, 0))
+                        m_texture_displacement_files.emplace(name, std::move(contents));
+                    else
+                        add_error("Error while reading texture displacement data");
+                }
                 else if (!dont_load_config && boost::algorithm::iequals(name, SLICE_INFO_CONFIG_FILE)) {
                     m_parsing_slice_info = true;
                     //extract slice info from archive
@@ -3301,6 +3326,59 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
         }
     }*/
 
+    // Restores one volume's texture displacement stack from the JSON it named. Called while the volume is
+    // being built, which is after the whole archive has been walked - so every file it can refer to is
+    // already extracted, and no deferral is needed.
+    //
+    // A missing or malformed JSON leaves the volume with no layers but keeps the paint mask it already
+    // loaded, which is the same state as a project saved by a build without the feature: recoverable by
+    // picking the texture again rather than a hard failure.
+    void _BBS_3MF_Importer::_apply_texture_displacement(ModelVolume &volume, const std::string &json_path)
+    {
+        const auto json = m_texture_displacement_files.find(json_path);
+        if (json == m_texture_displacement_files.end()) {
+            add_error("Missing texture displacement data: " + json_path);
+            return;
+        }
+        std::vector<TextureDisplacementLayer> layers;
+        TextureDisplacementOptions            options;
+        if (!texture_displacement_layers_from_json(json->second, layers, options)) {
+            add_error("Malformed texture displacement data: " + json_path);
+            return;
+        }
+        // A layer the archive carries no image for - saved while its texture had not been loaded, or
+        // written by a build that stored only the path - falls back to the file it came from. The
+        // importer copies every texture into the user's own library, so that path resolves on the
+        // machine the project was made on and quietly resolves nowhere else, which is the old
+        // behaviour: settings restored, pixels not.
+        const auto load_image_from_disk = [](TextureDisplacementLayer &layer) {
+            boost::system::error_code ec;
+            if (layer.path.empty() || !boost::filesystem::is_regular_file(layer.path, ec) || ec)
+                return;
+            boost::nowide::ifstream file(layer.path, std::ios::binary);
+            if (!file.good())
+                return;
+            std::vector<unsigned char> bytes((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>());
+            if (!bytes.empty())
+                layer.image_data = std::make_shared<std::vector<unsigned char>>(std::move(bytes));
+        };
+
+        for (TextureDisplacementLayer &layer : layers) {
+            if (!layer.path_in_3mf.empty()) {
+                if (const auto image = m_texture_displacement_files.find(layer.path_in_3mf);
+                    image != m_texture_displacement_files.end()) {
+                    layer.image_data = std::make_shared<std::vector<unsigned char>>(image->second.begin(),
+                                                                                    image->second.end());
+                    continue;
+                }
+                add_error("Missing texture displacement image: " + layer.path_in_3mf);
+            }
+            load_image_from_disk(layer);
+        }
+        volume.texture_displacement_layers  = std::move(layers);
+        volume.texture_displacement_options = options;
+    }
+
     void _BBS_3MF_Importer::_extract_embossed_svg_shape_file(const std::string &filename, mz_zip_archive &archive, const mz_zip_archive_file_stat &stat){
         assert(m_path_to_emboss_shape_files.find(filename) == m_path_to_emboss_shape_files.end());
         auto file = std::make_unique<std::string>(stat.m_uncomp_size, '\0');
@@ -3950,6 +4028,9 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
             m_curr_object->geometry.custom_seam.push_back(bbs_get_attribute_value_string(attributes, num_attributes, CUSTOM_SEAM_ATTR));
             m_curr_object->geometry.mmu_segmentation.push_back(bbs_get_attribute_value_string(attributes, num_attributes, MMU_SEGMENTATION_ATTR));
             m_curr_object->geometry.fuzzy_skin.push_back(bbs_get_attribute_value_string(attributes, num_attributes, CUSTOM_FUZZY_SKIN_ATTR));
+            for (int slot = 0; slot < int(TEXTURE_DISPLACEMENT_MAX_LAYERS); ++slot)
+                m_curr_object->geometry.texture_displacement[slot].push_back(
+                    bbs_get_attribute_value_string(attributes, num_attributes, TEXTURE_DISPLACEMENT_ATTRS[slot]));
             // BBS
             m_curr_object->geometry.face_properties.push_back(bbs_get_attribute_value_string(attributes, num_attributes, FACE_PROPERTY_ATTR));
         }
@@ -5276,6 +5357,18 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
                 volume->mmu_segmentation_facets.touch();
                 volume->fuzzy_skin_facets.shrink_to_fit();
                 volume->fuzzy_skin_facets.touch();
+                for (int slot = 0; slot < int(TEXTURE_DISPLACEMENT_MAX_LAYERS); ++slot) {
+                    const std::vector<std::string> &mask = sub_object->geometry.texture_displacement[slot];
+                    if (mask.empty())
+                        continue; // written by a build without the feature
+                    FacetsAnnotation &facets = volume->texture_displacement_facet(slot);
+                    facets.reserve(triangles_count);
+                    for (size_t i = 0; i < triangles_count && i < mask.size(); ++i)
+                        if (!mask[i].empty())
+                            facets.set_triangle_from_string(i, mask[i]);
+                    facets.shrink_to_fit();
+                    facets.touch();
+                }
             }
 
             volume->set_type(volume_data->part_type);
@@ -5291,6 +5384,8 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
             for (const Metadata& metadata : volume_data->metadata) {
                 if (metadata.key == NAME_KEY)
                     volume->name = metadata.value;
+                else if (metadata.key == TEXTURE_DISPLACEMENT_KEY)
+                    _apply_texture_displacement(*volume, metadata.value);
                 //else if ((metadata.key == MODIFIER_KEY) && (metadata.value == "1"))
 				//	volume->set_type(ModelVolumeType::PARAMETER_MODIFIER);
 				//for old format
@@ -5455,12 +5550,28 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
             volume->seam_facets.shrink_to_fit();
             volume->mmu_segmentation_facets.shrink_to_fit();
 
+            for (int slot = 0; slot < int(TEXTURE_DISPLACEMENT_MAX_LAYERS); ++slot) {
+                const std::vector<std::string> &mask = geometry.texture_displacement[slot];
+                if (mask.empty())
+                    continue; // written by a build without the feature
+                FacetsAnnotation &facets = volume->texture_displacement_facet(slot);
+                facets.reserve(triangles_count);
+                for (size_t i = 0; i < triangles_count; ++i) {
+                    const size_t index = volume_data.first_triangle_id + i;
+                    if (index < mask.size() && !mask[index].empty())
+                        facets.set_triangle_from_string(i, mask[index]);
+                }
+                facets.shrink_to_fit();
+                facets.touch();
+            }
             volume->set_type(volume_data.part_type);
 
             // apply the remaining volume's metadata
             for (const Metadata& metadata : volume_data.metadata) {
                 if (metadata.key == NAME_KEY)
                     volume->name = metadata.value;
+                else if (metadata.key == TEXTURE_DISPLACEMENT_KEY)
+                    _apply_texture_displacement(*volume, metadata.value);
                 //else if ((metadata.key == MODIFIER_KEY) && (metadata.value == "1"))
 				//	volume->set_type(ModelVolumeType::PARAMETER_MODIFIER);
 				//for old format
@@ -5757,6 +5868,9 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
             current_object->geometry.custom_seam.push_back(bbs_get_attribute_value_string(attributes, num_attributes, CUSTOM_SEAM_ATTR));
             current_object->geometry.mmu_segmentation.push_back(bbs_get_attribute_value_string(attributes, num_attributes, MMU_SEGMENTATION_ATTR));
             current_object->geometry.fuzzy_skin.push_back(bbs_get_attribute_value_string(attributes, num_attributes, CUSTOM_FUZZY_SKIN_ATTR));
+            for (int slot = 0; slot < int(TEXTURE_DISPLACEMENT_MAX_LAYERS); ++slot)
+                current_object->geometry.texture_displacement[slot].push_back(
+                    bbs_get_attribute_value_string(attributes, num_attributes, TEXTURE_DISPLACEMENT_ATTRS[slot]));
             // BBS
             current_object->geometry.face_properties.push_back(bbs_get_attribute_value_string(attributes, num_attributes, FACE_PROPERTY_ATTR));
         }
@@ -6760,6 +6874,9 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
         stream << " <Default Extension=\"rels\" ContentType=\"application/vnd.openxmlformats-package.relationships+xml\"/>\n";
         stream << " <Default Extension=\"model\" ContentType=\"application/vnd.ms-package.3dmanufacturing-3dmodel+xml\"/>\n";
         stream << " <Default Extension=\"png\" ContentType=\"image/png\"/>\n";
+        stream << " <Default Extension=\"jpg\" ContentType=\"image/jpeg\"/>\n";
+        stream << " <Default Extension=\"jpeg\" ContentType=\"image/jpeg\"/>\n";
+        stream << " <Default Extension=\"json\" ContentType=\"application/json\"/>\n";
         stream << " <Default Extension=\"gcode\" ContentType=\"text/x.gcode\"/>\n";
         stream << "</Types>";
 
@@ -7603,6 +7720,20 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
                     output_buffer += "\"";
                 }
 
+                // One attribute per texture displacement layer slot. Older readers ignore attributes they do
+                // not know, so a project written here still opens in a build without the feature - it just
+                // loses the paint, which is also all it could have done with it.
+                for (int slot = 0; slot < TEXTURE_DISPLACEMENT_MAX_LAYERS; ++slot) {
+                    const std::string texture_paint = volume->texture_displacement_facet(slot).get_triangle_as_string(i);
+                    if (texture_paint.empty())
+                        continue;
+                    output_buffer += " ";
+                    output_buffer += TEXTURE_DISPLACEMENT_ATTRS[slot];
+                    output_buffer += "=\"";
+                    output_buffer += texture_paint;
+                    output_buffer += "\"";
+                }
+
                 // BBS
                 if (i < its.properties.size()) {
                     std::string prop_str = its.properties[i].to_string();
@@ -8052,7 +8183,42 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
         return file_path;
     }
 
-    bool _BBS_3MF_Exporter::_add_model_config_file_to_archive(mz_zip_archive& archive, const Model& model, PlateDataPtrs& plate_data_list, const ObjectToObjectDataMap &objects_data, const DynamicPrintConfig& config, int export_plate_idx, bool save_gcode, bool use_loaded_id)
+    // Writes a volume's texture displacement stack into the archive and points the volume's metadata at it.
+// The layer settings go in as JSON and each layer's texture as the image file it was loaded from, both
+// referenced by path - the same split EmbossShape makes for its SVG. The image deliberately stays out of
+// the XML: it is binary and routinely megabytes, and base64 in an attribute would bloat the one file
+// every reader has to parse just to list the objects.
+static void add_texture_displacement(std::stringstream &stream, const ModelVolume &volume, mz_zip_archive &archive,
+                                     const std::string &id)
+{
+    if (volume.texture_displacement_layers.empty())
+        return;
+
+    // A copy, because path_in_3mf is only meaningful inside the archive being written and the volume
+    // being exported is const (and may be saved again, elsewhere, with different paths).
+    std::vector<TextureDisplacementLayer> layers = volume.texture_displacement_layers;
+    for (TextureDisplacementLayer &layer : layers) {
+        layer.path_in_3mf.clear();
+        if (!layer.image_data || layer.image_data->empty())
+            continue;
+        // Always .png: the importer converts whatever the user picked (jpg, bmp, ...) to an 8-bit
+        // greyscale PNG, so image_data is PNG whatever layer.path happens to be named.
+        const std::string path = std::string(TEXTURE_DISPLACEMENT_DIR) + id + "_" + std::to_string(layer.slot) + ".png";
+        // No deflate: a PNG is already compressed, so a second pass only costs time.
+        if (mz_zip_writer_add_mem(&archive, path.c_str(), layer.image_data->data(), layer.image_data->size(),
+                                  MZ_NO_COMPRESSION))
+            layer.path_in_3mf = path;
+    }
+
+    const std::string json      = texture_displacement_layers_to_json(layers, volume.texture_displacement_options);
+    const std::string json_path = std::string(TEXTURE_DISPLACEMENT_DIR) + id + ".json";
+    if (!mz_zip_writer_add_mem(&archive, json_path.c_str(), json.data(), json.size(), MZ_DEFAULT_COMPRESSION))
+        return;
+    stream << "      <" << METADATA_TAG << " " << KEY_ATTR << "=\"" << TEXTURE_DISPLACEMENT_KEY << "\" "
+           << VALUE_ATTR << "=\"" << xml_escape(json_path) << "\"/>\n";
+}
+
+bool _BBS_3MF_Exporter::_add_model_config_file_to_archive(mz_zip_archive& archive, const Model& model, PlateDataPtrs& plate_data_list, const ObjectToObjectDataMap &objects_data, const DynamicPrintConfig& config, int export_plate_idx, bool save_gcode, bool use_loaded_id)
     {
         std::stringstream stream;
         // Store mesh transformation in full precision, as the volumes are stored transformed and they need to be transformed back
@@ -8163,6 +8329,8 @@ void PlateData::parse_filament_info(GCodeProcessorResult *result)
                             if (const std::optional<EmbossShape> &es = volume->emboss_shape; es.has_value()) {
                                 to_xml(stream, *es, *volume, archive, m_fullpath_sources);
                             }
+
+                            add_texture_displacement(stream, *volume, archive, std::to_string(volume->id().id));
                     
                             if (const std::optional<TextConfiguration> &tc = volume->text_configuration;
                                 tc.has_value())

src/libslic3r/TextureDisplacement.cpp

@@ -19,6 +19,7 @@
 #include <mutex>
 #include <numeric>
 #include <optional>
+#include "nlohmann/json.hpp"
 #include <queue>
 #include <ratio>
 #include <string>
@@ -5141,5 +5142,251 @@ indexed_triangle_set cut_mesh_at_steps(const indexed_triangle_set &mesh, const s
     return out;
 }
 
+// ---------------------------------------------------------------------------------------------
+// Project persistence. See the declarations in TextureDisplacement.hpp for why this is JSON rather
+// than the cereal stream next to them.
+// ---------------------------------------------------------------------------------------------
+namespace {
+
+nlohmann::json vec2_to_json(const Vec2f &v) { return nlohmann::json::array({ v.x(), v.y() }); }
+nlohmann::json vec3_to_json(const Vec3f &v) { return nlohmann::json::array({ v.x(), v.y(), v.z() }); }
+
+Vec2f vec2_from_json(const nlohmann::json &j, const Vec2f &fallback)
+{
+    if (!j.is_array() || j.size() != 2)
+        return fallback;
+    return Vec2f(j[0].get<float>(), j[1].get<float>());
+}
+Vec3f vec3_from_json(const nlohmann::json &j, const Vec3f &fallback)
+{
+    if (!j.is_array() || j.size() != 3)
+        return fallback;
+    return Vec3f(j[0].get<float>(), j[1].get<float>(), j[2].get<float>());
+}
+
+// Reads key `k` into `out` when it is present and of the expected type, leaving `out` alone otherwise.
+// That "leave it alone" is the whole point: every member starts at its struct default, so a project
+// written by an older build simply keeps the defaults for whatever it did not know about.
+template<class T> void read(const nlohmann::json &j, const char *k, T &out)
+{
+    const auto it = j.find(k);
+    if (it == j.end())
+        return;
+    try {
+        out = it->get<T>();
+    } catch (...) {
+    }
+}
+void read_enum(const nlohmann::json &j, const char *k, int &out)
+{
+    const auto it = j.find(k);
+    if (it != j.end() && it->is_number_integer())
+        out = it->get<int>();
+}
+
+} // namespace
+
+std::string texture_displacement_layers_to_json(const std::vector<TextureDisplacementLayer> &layers,
+                                                const TextureDisplacementOptions            &options)
+{
+    nlohmann::json root;
+    root["version"] = 1;
+
+    nlohmann::json &opt = root["options"];
+    opt["displace_border"]    = options.displace_border;
+    opt["smooth_enabled"]     = options.smooth_enabled;
+    opt["smooth_strength"]    = options.smooth_strength;
+    opt["smooth_iterations"]  = options.smooth_iterations;
+    opt["smooth_skip_border"] = options.smooth_skip_border;
+    opt["pipeline_v2"]        = options.pipeline_v2;
+    opt["v2_refine_mm"]       = options.v2_refine_mm;
+    opt["v2_regularize"]      = options.v2_regularize;
+    opt["v2_max_triangles_k"] = options.v2_max_triangles_k;
+    opt["v2_relocate"]        = options.v2_relocate;
+    opt["v2_flip_edges"]      = options.v2_flip_edges;
+    opt["color_mix_enabled"]  = options.color_mix_enabled;
+    opt["color_mix_mode"]     = int(options.color_mix_mode);
+    opt["color_despeckle"]    = options.color_despeckle;
+    opt["active_slot"]        = options.active_slot;
+    opt["panel_mode"]         = options.panel_mode;
+
+    nlohmann::json &arr = root["layers"];
+    arr                 = nlohmann::json::array();
+    for (const TextureDisplacementLayer &l : layers) {
+        nlohmann::json j;
+        j["slot"]        = l.slot;
+        j["name"]        = l.name;
+        j["path"]        = l.path;
+        j["path_in_3mf"] = l.path_in_3mf;
+
+        j["depth_mm"]     = l.depth_mm;
+        j["tiling_scale"] = l.tiling_scale;
+        j["rotation_deg"] = l.rotation_deg;
+        j["offset"]       = vec2_to_json(l.offset);
+        j["invert"]       = l.invert;
+        j["midlevel"]     = l.midlevel;
+        j["smoothing"]    = l.smoothing;
+
+        j["edge_smoothing"]        = l.edge_smoothing;
+        j["edge_smoothing_amount"] = l.edge_smoothing_amount;
+        j["auto_connect_islands"]  = l.auto_connect_islands;
+
+        j["tile_enabled"]      = l.tile_enabled;
+        j["tile_method"]       = int(l.tile_method);
+        j["projection_method"] = int(l.projection_method);
+        j["blend_mode"]        = int(l.blend_mode);
+        j["color_enabled"]     = l.color_enabled;
+
+        j["lscm_seam_angle_deg"] = l.lscm_seam_angle_deg;
+        j["island_padding_mm"]   = l.island_padding_mm;
+
+        j["view_project_right"]      = vec3_to_json(l.view_project_right);
+        j["view_project_up"]         = vec3_to_json(l.view_project_up);
+        j["view_project_projective"] = l.view_project_projective;
+        j["view_project_matrix"]     = l.view_project_matrix;
+
+        // Flat pairs rather than nested arrays: shorter, and the reader can simply ignore a trailing
+        // odd element instead of having to validate every sub-array.
+        nlohmann::json &seams = j["lscm_seam_edges"];
+        seams                 = nlohmann::json::array();
+        for (const auto &[a, b] : l.lscm_seam_edges) {
+            seams.push_back(a);
+            seams.push_back(b);
+        }
+
+        nlohmann::json &islands = j["islands"];
+        islands                 = nlohmann::json::array();
+        for (const TextureIsland &island : l.islands)
+            islands.push_back(nlohmann::json::array(
+                { island.offset.x(), island.offset.y(), island.rotation_deg, island.scale }));
+
+        j["island_groups"] = l.island_groups;
+
+        nlohmann::json &overrides = j["lscm_uv_overrides"];
+        overrides                 = nlohmann::json::array();
+        for (const auto &[key, uv] : l.lscm_uv_overrides)
+            overrides.push_back(nlohmann::json::array({ key, uv.x(), uv.y() }));
+
+        arr.push_back(std::move(j));
+    }
+    return root.dump();
+}
+
+bool texture_displacement_layers_from_json(const std::string                     &text,
+                                           std::vector<TextureDisplacementLayer> &layers,
+                                           TextureDisplacementOptions            &options)
+{
+    nlohmann::json root;
+    try {
+        root = nlohmann::json::parse(text);
+    } catch (...) {
+        return false;
+    }
+    if (!root.is_object())
+        return false;
+
+    TextureDisplacementOptions out_options;
+    if (const auto it = root.find("options"); it != root.end() && it->is_object()) {
+        const nlohmann::json &opt = *it;
+        read(opt, "displace_border", out_options.displace_border);
+        read(opt, "smooth_enabled", out_options.smooth_enabled);
+        read(opt, "smooth_strength", out_options.smooth_strength);
+        read(opt, "smooth_iterations", out_options.smooth_iterations);
+        read(opt, "smooth_skip_border", out_options.smooth_skip_border);
+        read(opt, "pipeline_v2", out_options.pipeline_v2);
+        read(opt, "v2_refine_mm", out_options.v2_refine_mm);
+        read(opt, "v2_regularize", out_options.v2_regularize);
+        read(opt, "v2_max_triangles_k", out_options.v2_max_triangles_k);
+        read(opt, "v2_relocate", out_options.v2_relocate);
+        read(opt, "v2_flip_edges", out_options.v2_flip_edges);
+        read(opt, "color_mix_enabled", out_options.color_mix_enabled);
+        read(opt, "color_despeckle", out_options.color_despeckle);
+        int mix_mode = int(out_options.color_mix_mode);
+        read_enum(opt, "color_mix_mode", mix_mode);
+        out_options.color_mix_mode = ColorMixMode(std::clamp(mix_mode, 0, 2));
+        read(opt, "active_slot", out_options.active_slot);
+        read(opt, "panel_mode", out_options.panel_mode);
+        out_options.active_slot = std::clamp(out_options.active_slot, 0, int(TEXTURE_DISPLACEMENT_MAX_LAYERS) - 1);
+        out_options.panel_mode  = std::clamp(out_options.panel_mode, 0, 1);
+    }
+
+    std::vector<TextureDisplacementLayer> out_layers;
+    if (const auto it = root.find("layers"); it != root.end() && it->is_array()) {
+        for (const nlohmann::json &j : *it) {
+            if (!j.is_object())
+                continue;
+            TextureDisplacementLayer l;
+            read(j, "slot", l.slot);
+            read(j, "name", l.name);
+            read(j, "path", l.path);
+            read(j, "path_in_3mf", l.path_in_3mf);
+
+            read(j, "depth_mm", l.depth_mm);
+            read(j, "tiling_scale", l.tiling_scale);
+            read(j, "rotation_deg", l.rotation_deg);
+            if (const auto o = j.find("offset"); o != j.end())
+                l.offset = vec2_from_json(*o, l.offset);
+            read(j, "invert", l.invert);
+            read(j, "midlevel", l.midlevel);
+            read(j, "smoothing", l.smoothing);
+
+            read(j, "edge_smoothing", l.edge_smoothing);
+            read(j, "edge_smoothing_amount", l.edge_smoothing_amount);
+            read(j, "auto_connect_islands", l.auto_connect_islands);
+
+            read(j, "tile_enabled", l.tile_enabled);
+            read(j, "color_enabled", l.color_enabled);
+            int tile_method = int(l.tile_method), projection = int(l.projection_method), blend = int(l.blend_mode);
+            read_enum(j, "tile_method", tile_method);
+            read_enum(j, "projection_method", projection);
+            read_enum(j, "blend_mode", blend);
+            l.tile_method       = TextureTileMethod(tile_method);
+            l.projection_method = TextureProjectionMethod(std::clamp(projection, 0, 4));
+            l.blend_mode        = TextureBlendMode(blend);
+
+            read(j, "lscm_seam_angle_deg", l.lscm_seam_angle_deg);
+            read(j, "island_padding_mm", l.island_padding_mm);
+
+            if (const auto v = j.find("view_project_right"); v != j.end())
+                l.view_project_right = vec3_from_json(*v, l.view_project_right);
+            if (const auto v = j.find("view_project_up"); v != j.end())
+                l.view_project_up = vec3_from_json(*v, l.view_project_up);
+            read(j, "view_project_projective", l.view_project_projective);
+            if (const auto v = j.find("view_project_matrix"); v != j.end() && v->is_array() && v->size() == 12)
+                for (size_t i = 0; i < 12; ++i)
+                    l.view_project_matrix[i] = (*v)[i].get<float>();
+
+            if (const auto v = j.find("lscm_seam_edges"); v != j.end() && v->is_array())
+                for (size_t i = 0; i + 1 < v->size(); i += 2)
+                    l.lscm_seam_edges.emplace_back((*v)[i].get<int>(), (*v)[i + 1].get<int>());
+
+            if (const auto v = j.find("islands"); v != j.end() && v->is_array())
+                for (const nlohmann::json &e : *v) {
+                    if (!e.is_array() || e.size() != 4)
+                        continue;
+                    TextureIsland island;
+                    island.offset       = Vec2f(e[0].get<float>(), e[1].get<float>());
+                    island.rotation_deg = e[2].get<float>();
+                    island.scale        = e[3].get<float>();
+                    l.islands.push_back(island);
+                }
+
+            read(j, "island_groups", l.island_groups);
+
+            if (const auto v = j.find("lscm_uv_overrides"); v != j.end() && v->is_array())
+                for (const nlohmann::json &e : *v) {
+                    if (!e.is_array() || e.size() != 3)
+                        continue;
+                    l.lscm_uv_overrides.emplace_back(e[0].get<int>(), Vec2f(e[1].get<float>(), e[2].get<float>()));
+                }
+
+            out_layers.push_back(std::move(l));
+        }
+    }
+
+    layers  = std::move(out_layers);
+    options = out_options;
+    return true;
+}
 
 } // namespace Slic3r

src/libslic3r/TextureDisplacement.hpp

@@ -412,16 +412,40 @@ struct TextureDisplacementOptions
     // finer than the mesh leaves behind, without eating features that are genuinely a facet wide.
     int          color_despeckle   = 2;
 
+    // Where the panel was left, rather than anything the bake reads. It lives with the volume because
+    // that is what it describes: reopening a project should put the user back on the layer they were
+    // editing, in the mode they were editing it in, not on slot 0 in Standard.
+    int active_slot = 0;
+    int panel_mode  = 0; // 0 Standard, 1 Pro
+
     template<class Archive> void serialize(Archive &ar)
     {
         int mix_mode = int(color_mix_mode);
         ar(displace_border, smooth_enabled, smooth_strength, smooth_iterations, smooth_skip_border,
            pipeline_v2, v2_refine_mm, v2_regularize, v2_max_triangles_k,
-           v2_relocate, color_mix_enabled, mix_mode, color_despeckle);
+           v2_relocate, v2_flip_edges, color_mix_enabled, mix_mode, color_despeckle,
+           active_slot, panel_mode);
         color_mix_mode = ColorMixMode(mix_mode);
     }
 };
 
+// Project persistence (see bbs_3mf.cpp). The layer stack and the per-volume options are written to the
+// .3mf as JSON rather than through the cereal save()/load() above: those two are positional and
+// unversioned, which is right for the undo/redo stack they serve (one session, one binary) but would
+// make every future field a project-breaking change. A JSON object tolerates both directions - an
+// unknown key is ignored, a missing one keeps the member's default - so old projects keep loading and
+// new ones degrade gracefully in older builds.
+//
+// The texture image itself is *not* in here. It is a binary blob that belongs in the archive as a file
+// of its own, exactly as EmbossShape stores its SVG; `path_in_3mf` names that file, and the caller is
+// responsible for writing it and for filling `image_data` back in on load.
+std::string texture_displacement_layers_to_json(const std::vector<TextureDisplacementLayer> &layers,
+                                                const TextureDisplacementOptions            &options);
+// Returns false and leaves both outputs untouched when the text is not valid JSON.
+bool texture_displacement_layers_from_json(const std::string                      &text,
+                                           std::vector<TextureDisplacementLayer>  &layers,
+                                           TextureDisplacementOptions             &options);
+
 // How much detail a height texture carries: central differences of the grey image, the mean gradient
 // and the share of texels steeper than 30 grey levels, mapped to how many texels one mesh edge may
 // span (1 for a hard-edged image, 4 for a smooth one). Cached per image, like the decode.

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.cpp

@@ -3329,6 +3329,7 @@ const ModelVolume* GLGizmoTextureDisplacement::texture_volume() const
 
 void GLGizmoTextureDisplacement::update_model_object()
 {
+    store_panel_state();
     bool         updated = false;
     ModelObject *mo      = m_c->selection_info()->model_object();
     int          idx     = -1;
@@ -3364,6 +3365,24 @@ void GLGizmoTextureDisplacement::update_from_model_object(bool first_update)
 {
     wxBusyCursor wait;
 
+    // Opening the gizmo puts the panel back where it was left: the layer and the mode come off the
+    // volume, because they are the user's place in this model's stack, and the dock state off the
+    // application config, because it is about their window. Only on open - this also runs on an
+    // undo/redo and on a layer switch, where overriding what the user is doing now would be wrong.
+    if (first_update) {
+        if (const ModelVolume *mv = texture_volume(); mv != nullptr) {
+            const TextureDisplacementOptions &opts = mv->texture_displacement_options;
+            m_panel_mode = std::clamp(opts.panel_mode, 0, 1);
+            // Only if that slot still holds a layer: the stack can have been edited by anything that
+            // does not go through the panel, and a selection pointing at nothing shows an empty panel.
+            const auto &stack = mv->texture_displacement_layers;
+            if (std::any_of(stack.begin(), stack.end(),
+                            [&opts](const TextureDisplacementLayer &l) { return l.slot == opts.active_slot; }))
+                m_active_layer_slot = opts.active_slot;
+        }
+        m_undocked = wxGetApp().app_config->get_bool(UNDOCKED_CONFIG_KEY);
+    }
+
     const ModelObject *mo = m_c->selection_info()->model_object();
     m_triangle_selectors.clear();
 
@@ -3409,6 +3428,14 @@ void GLGizmoTextureDisplacement::update_from_model_object(bool first_update)
     rebuild_preview();
 }
 
+void GLGizmoTextureDisplacement::store_panel_state()
+{
+    if (ModelVolume *mv = texture_volume(); mv != nullptr) {
+        mv->texture_displacement_options.active_slot = m_active_layer_slot;
+        mv->texture_displacement_options.panel_mode  = m_panel_mode;
+    }
+}
+
 void GLGizmoTextureDisplacement::set_active_layer(int slot)
 {
     if (slot == m_active_layer_slot)
@@ -3417,6 +3444,7 @@ void GLGizmoTextureDisplacement::set_active_layer(int slot)
     // reflect - otherwise they would be silently lost.
     update_model_object();
     m_active_layer_slot = slot;
+    store_panel_state();
     update_from_model_object(false);
     // The on-canvas gizmo (if on) is anchored to whichever layer is active - keep it in sync
     // instead of leaving it pointing at the previous layer's (now stale) paint patch.
@@ -5590,6 +5618,7 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                                    "not what you wanted and you know why."));
             if (clicked && !on) {
                 m_panel_mode = m;
+                store_panel_state();
                 if (!pro_mode()) {
                     // Leaving the subdivision preview open would strand a wireframe whose controls just
                     // disappeared, so close it as part of the switch.
@@ -5612,6 +5641,7 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                         _L("Detach this panel so it can be dragged anywhere over the 3D view, or dock it back beside "
                            "the toolbar.")))
             m_undocked = !m_undocked;
+            wxGetApp().app_config->set_bool(UNDOCKED_CONFIG_KEY, m_undocked);
     }
     ImGui::Separator();
 

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.hpp

@@ -206,6 +206,9 @@ private:
     // Standard is active so what Preview shows is always what Bake will do. Returns true if it actually
     // changed something, so the caller can invalidate the preview.
     bool apply_standard_mode_presets(ModelVolume *mv);
+    // Copies the panel's own state (active layer, Standard/Pro) onto the volume, so the project file
+    // can carry it. Cheap and idempotent - called wherever either of the two changes.
+    void store_panel_state();
     // Standard mode's Bake: remesh to an even density, refine where the texture bends, then displace.
     // The order matters and is the whole reason this is one button - a height map can only move
     // existing vertices, so the mesh has to be prepared first, and remeshing after painting would drop
@@ -904,9 +907,12 @@ private:
     PatchUnwrap m_uv_editor_unwrap;
 
     // When set, the panel is a free-floating window the user can drag anywhere (with a title bar to
-    // grab), instead of being pinned to the right of the gizmo toolbar. Persisted across gizmo
-    // open/close within a session, so the choice sticks while working.
+    // grab), instead of being pinned to the right of the gizmo toolbar. Kept in the application
+    // config rather than in the project: it describes the user's window, not the model, so opening
+    // someone else's project must not move their panel.
     bool m_undocked = false;
+    // The config key behind m_undocked.
+    static constexpr const char *UNDOCKED_CONFIG_KEY = "texture_displacement_panel_undocked";
 
     // Smooth scrolling for the panel body (everything between the header and the pinned Bake footer).
     // ImGui jumps a fixed number of lines per wheel notch, which on tall layer cards reads as a hard

tests/libslic3r/test_texture_displacement.cpp

@@ -2135,3 +2135,146 @@ TEST_CASE("A second bake beside a first comes out as fine as a single bake", "[T
     CHECK(second <= single * 5 / 4);
 }
 
+
+// The .3mf stores the layer stack as JSON (see texture_displacement_layers_to_json). Two properties
+// matter: everything the UV editor and the panel can set has to survive a round trip, and a document
+// written by a build that knew fewer fields has to keep loading, with the missing ones left at their
+// defaults rather than zeroed.
+TEST_CASE("Texture displacement layers survive a JSON round trip", "[TextureDisplacement]")
+{
+    std::vector<TextureDisplacementLayer> layers(2);
+    TextureDisplacementLayer             &a = layers[0];
+    a.slot                 = 0;
+    a.name                 = "Bark";
+    a.path                 = "/textures/bark.png";
+    a.depth_mm             = 1.25f;
+    a.tiling_scale         = 7.5f;
+    a.rotation_deg         = 30.f;
+    a.offset               = Vec2f(0.25f, -0.5f);
+    a.invert               = true;
+    a.midlevel             = 0.125f;
+    a.smoothing            = 0.75f;
+    a.edge_smoothing       = true;
+    a.edge_smoothing_amount = 0.25f;
+    a.auto_connect_islands = false;
+    a.tile_enabled         = false;
+    a.tile_method          = TextureTileMethod::MirroredRepeat;
+    a.projection_method    = TextureProjectionMethod::LSCM;
+    a.blend_mode           = TextureBlendMode::Subtract;
+    a.color_enabled        = true;
+    a.lscm_seam_angle_deg  = 45.f;
+    a.island_padding_mm    = 0.5f;
+    a.lscm_seam_edges      = { { 1, 2 }, { 3, 5 } };
+    a.islands              = { TextureIsland{ Vec2f(1.f, 2.f), 15.f, 1.5f }, TextureIsland{} };
+    a.island_groups        = { 0, 0 };
+    a.lscm_uv_overrides    = { { -4, Vec2f(0.5f, 0.75f) } };
+
+    TextureDisplacementLayer &b = layers[1];
+    b.slot                    = 1;
+    b.projection_method       = TextureProjectionMethod::ViewProjected;
+    b.view_project_right      = Vec3f(0.f, 1.f, 0.f);
+    b.view_project_up         = Vec3f(0.f, 0.f, 1.f);
+    b.view_project_projective = true;
+    for (size_t i = 0; i < b.view_project_matrix.size(); ++i)
+        b.view_project_matrix[i] = float(i) + 0.5f;
+
+    TextureDisplacementOptions options;
+    options.displace_border   = false;
+    options.smooth_enabled    = true;
+    options.smooth_strength   = 0.6f;
+    options.smooth_iterations = 5;
+    options.pipeline_v2       = false;
+    options.v2_max_triangles_k = 250;
+    options.color_mix_mode    = ColorMixMode::XYDither;
+    options.color_despeckle   = 4;
+    options.active_slot       = 3;
+    options.panel_mode        = 1;
+
+    const std::string json = texture_displacement_layers_to_json(layers, options);
+
+    std::vector<TextureDisplacementLayer> read_layers;
+    TextureDisplacementOptions            read_options;
+    REQUIRE(texture_displacement_layers_from_json(json, read_layers, read_options));
+    REQUIRE(read_layers.size() == layers.size());
+
+    const TextureDisplacementLayer &ra = read_layers[0];
+    CHECK(ra.name == a.name);
+    CHECK(ra.path == a.path);
+    CHECK_THAT(ra.depth_mm, WithinAbs(a.depth_mm, 1e-6f));
+    CHECK_THAT(ra.tiling_scale, WithinAbs(a.tiling_scale, 1e-6f));
+    CHECK_THAT(ra.rotation_deg, WithinAbs(a.rotation_deg, 1e-6f));
+    CHECK(ra.offset.isApprox(a.offset));
+    CHECK(ra.invert == a.invert);
+    CHECK_THAT(ra.midlevel, WithinAbs(a.midlevel, 1e-6f));
+    CHECK_THAT(ra.smoothing, WithinAbs(a.smoothing, 1e-6f));
+    CHECK(ra.edge_smoothing == a.edge_smoothing);
+    CHECK_THAT(ra.edge_smoothing_amount, WithinAbs(a.edge_smoothing_amount, 1e-6f));
+    CHECK(ra.auto_connect_islands == a.auto_connect_islands);
+    CHECK(ra.tile_enabled == a.tile_enabled);
+    CHECK(ra.tile_method == a.tile_method);
+    CHECK(ra.projection_method == a.projection_method);
+    CHECK(ra.blend_mode == a.blend_mode);
+    CHECK(ra.color_enabled == a.color_enabled);
+    CHECK_THAT(ra.lscm_seam_angle_deg, WithinAbs(a.lscm_seam_angle_deg, 1e-6f));
+    CHECK_THAT(ra.island_padding_mm, WithinAbs(a.island_padding_mm, 1e-6f));
+    CHECK(ra.lscm_seam_edges == a.lscm_seam_edges);
+    REQUIRE(ra.islands.size() == a.islands.size());
+    CHECK(ra.islands[0].offset.isApprox(a.islands[0].offset));
+    CHECK_THAT(ra.islands[0].rotation_deg, WithinAbs(a.islands[0].rotation_deg, 1e-6f));
+    CHECK_THAT(ra.islands[0].scale, WithinAbs(a.islands[0].scale, 1e-6f));
+    CHECK(ra.island_groups == a.island_groups);
+    REQUIRE(ra.lscm_uv_overrides.size() == 1);
+    CHECK(ra.lscm_uv_overrides[0].first == -4);
+    CHECK(ra.lscm_uv_overrides[0].second.isApprox(Vec2f(0.5f, 0.75f)));
+
+    const TextureDisplacementLayer &rb = read_layers[1];
+    CHECK(rb.projection_method == TextureProjectionMethod::ViewProjected);
+    CHECK(rb.view_project_right.isApprox(b.view_project_right));
+    CHECK(rb.view_project_up.isApprox(b.view_project_up));
+    CHECK(rb.view_project_projective);
+    CHECK(rb.view_project_matrix == b.view_project_matrix);
+
+    CHECK(read_options.displace_border == options.displace_border);
+    CHECK(read_options.smooth_enabled == options.smooth_enabled);
+    CHECK_THAT(read_options.smooth_strength, WithinAbs(options.smooth_strength, 1e-6f));
+    CHECK(read_options.smooth_iterations == options.smooth_iterations);
+    CHECK(read_options.pipeline_v2 == options.pipeline_v2);
+    CHECK(read_options.v2_max_triangles_k == options.v2_max_triangles_k);
+    CHECK(read_options.color_mix_mode == options.color_mix_mode);
+    CHECK(read_options.color_despeckle == options.color_despeckle);
+    // Where the panel was left comes back with the rest, so a reopened project is on the same layer.
+    CHECK(read_options.active_slot == options.active_slot);
+    CHECK(read_options.panel_mode == options.panel_mode);
+}
+
+TEST_CASE("Texture displacement JSON keeps defaults for keys it does not carry", "[TextureDisplacement]")
+{
+    // What a build that knew fewer fields would have written: one layer, almost nothing set.
+    const std::string sparse = R"({"version":1,"layers":[{"slot":2,"name":"Old","depth_mm":0.75}]})";
+
+    std::vector<TextureDisplacementLayer> layers;
+    TextureDisplacementOptions            options;
+    REQUIRE(texture_displacement_layers_from_json(sparse, layers, options));
+    REQUIRE(layers.size() == 1);
+
+    const TextureDisplacementLayer  &l = layers[0];
+    const TextureDisplacementLayer   fresh;
+    const TextureDisplacementOptions defaults;
+    CHECK(l.slot == 2);
+    CHECK(l.name == "Old");
+    CHECK_THAT(l.depth_mm, WithinAbs(0.75f, 1e-6f));
+    // Everything absent keeps the struct's own default rather than becoming zero.
+    CHECK_THAT(l.tiling_scale, WithinAbs(fresh.tiling_scale, 1e-6f));
+    CHECK(l.auto_connect_islands == fresh.auto_connect_islands);
+    CHECK(l.tile_enabled == fresh.tile_enabled);
+    CHECK(l.projection_method == fresh.projection_method);
+    CHECK_THAT(l.lscm_seam_angle_deg, WithinAbs(fresh.lscm_seam_angle_deg, 1e-6f));
+    CHECK(options.color_mix_mode == defaults.color_mix_mode);
+    CHECK(options.pipeline_v2 == defaults.pipeline_v2);
+    CHECK(options.active_slot == defaults.active_slot);
+    CHECK(options.panel_mode == defaults.panel_mode);
+
+    std::vector<TextureDisplacementLayer> unused_layers;
+    TextureDisplacementOptions            unused_options;
+    CHECK(!texture_displacement_layers_from_json("not json at all", unused_layers, unused_options));
+}