Keep the texture picker from stalling on open

Opening the texture picker decoded every texture in the expanded sections
on the GUI thread in one frame, each one twice at full size. Only the
visible tiles now load, at most a couple per frame, and the rest fill in
over the following frames.

The library validation no longer decodes the pixels: a header-only check,
is_decodable_8bit_png(), accepts exactly what the two decoders take.

deps/JPEG/JPEG.cmake

@@ -1,7 +1,22 @@
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+    if (JPEG_VERSION STREQUAL "6")
+        message("Using Jpeg Lib 62")
+        set(jpeg_flag "")
+    elseif (JPEG_VERSION STREQUAL "7")
+        message("Using Jpeg Lib 70")
+        set(jpeg_flag "-DWITH_JPEG7=ON")
+    else ()
+        message("Using Jpeg Lib 80")
+        set(jpeg_flag "-DWITH_JPEG8=ON")
+    endif ()
+endif()
+
 orcaslicer_add_cmake_project(JPEG
-    URL https://github.com/libjpeg-turbo/libjpeg-turbo/archive/refs/tags/3.2.0.zip
-    URL_HASH SHA256=1b4c2cb6cba1ca5e53b9e85eeeab02154cab4b70894c96e97a9c747a26d19d63
+    URL https://github.com/libjpeg-turbo/libjpeg-turbo/archive/refs/tags/3.0.1.zip
+    URL_HASH SHA256=d6d99e693366bc03897677650e8b2dfa76b5d6c54e2c9e70c03f0af821b0a52f
+    DEPENDS ${ZLIB_PKG}
     CMAKE_ARGS
         -DENABLE_SHARED=OFF
         -DENABLE_STATIC=ON
+        ${jpeg_flag}
 )

scripts/flatpak/com.orcaslicer.OrcaSlicer.yml

@@ -336,10 +336,10 @@ modules:
         sha256: 3d22d46c566b1761a0e15ea397589b3a5f36ac09b7c785382e6470156c04247f
         dest: external-packages/PNG
 
-      # libjpeg-turbo 3.2.0
+      # libjpeg-turbo 3.0.1
       - type: file
-        url: https://github.com/libjpeg-turbo/libjpeg-turbo/archive/refs/tags/3.2.0.zip
-        sha256: 1b4c2cb6cba1ca5e53b9e85eeeab02154cab4b70894c96e97a9c747a26d19d63
+        url: https://github.com/libjpeg-turbo/libjpeg-turbo/archive/refs/tags/3.0.1.zip
+        sha256: d6d99e693366bc03897677650e8b2dfa76b5d6c54e2c9e70c03f0af821b0a52f
         dest: external-packages/JPEG
 
       # Freetype 2.12.1

src/libslic3r/PNGReadWrite.cpp

@@ -211,6 +211,35 @@ bool decode_colored_png(const ReadBuf &in_buf, ImageColorscale &out_img)
     return decode_colored_png(stream, out_img);
 }
 
+bool is_decodable_8bit_png(const ReadBuf &pngbuf)
+{
+    static const constexpr int PNG_SIG_BYTES = 8;
+
+    struct ReadBufStream stream{pngbuf};
+    std::vector<png_byte> sig(PNG_SIG_BYTES, 0);
+    stream.read(sig.data(), PNG_SIG_BYTES);
+    if (!png_check_sig(sig.data(), PNG_SIG_BYTES))
+        return false;
+
+    PNGDescr dsc;
+    dsc.png = png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
+    if (!dsc.png)
+        return false;
+    dsc.info = png_create_info_struct(dsc.png);
+    if (!dsc.info)
+        return false;
+
+    if (!png_read_header_guarded(dsc.png, dsc.info, &stream, PNG_SIG_BYTES))
+        return false;
+
+    const size_t color_type = png_get_color_type(dsc.png, dsc.info);
+    const size_t bit_depth  = png_get_bit_depth(dsc.png, dsc.info);
+    const bool   grey       = color_type == PNG_COLOR_TYPE_GRAY;
+    const bool   colour     = color_type == PNG_COLOR_TYPE_RGB || color_type == PNG_COLOR_TYPE_RGB_ALPHA;
+    return png_get_image_width(dsc.png, dsc.info) > 0 && png_get_image_height(dsc.png, dsc.info) > 0 &&
+           bit_depth == 8 && (grey || colour);
+}
+
 
 // Down to earth function to store a packed RGB image to file. Mostly useful for debugging purposes.
 // Based on https://www.lemoda.net/c/write-png/

src/libslic3r/PNGReadWrite.hpp

@@ -50,6 +50,9 @@ struct ReadBuf { const void *buf = nullptr; const size_t sz = 0; };
 
 bool is_png(const ReadBuf &pngbuf);
 
+// True if decode_png() or decode_colored_png() would accept these bytes, judged from the header alone.
+bool is_decodable_8bit_png(const ReadBuf &pngbuf);
+
 struct ReadBufStream: public IStream {
     const ReadBuf &rbuf_ref;
     size_t pos = 0;

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.cpp

@@ -174,6 +174,10 @@ constexpr int HEIGHT_TEX_MAX_PX = 2048;
 // The full-size image is only ever adjusted once, on commit.
 constexpr int ADJUST_PREVIEW_MAX_PX = 384;
 
+// Library textures the texture picker decodes per frame. Each decode runs on the GUI thread, so the
+// rest of the visible tiles fill in over the following frames instead of in one stall.
+constexpr int PICKER_LOADS_PER_FRAME = 2;
+
 // 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.
@@ -4331,6 +4335,8 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
     std::optional<TextureLibraryEntry> to_remove;
     bool                               import_clicked = false;
     bool                               download_clicked = false;
+    int                                loads_left       = PICKER_LOADS_PER_FRAME;
+    bool                               loads_deferred   = false;
 
     // Tiles are placed on the four-column grid explicitly rather than flowed with SameLine(): a user tile
     // overlays a remove button on its corner, and that button would otherwise be "the previous item" the
@@ -4348,11 +4354,30 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
     };
     // One section's tiles, in the order the section holds them (shipped alphabetically, pack textures by
     // name, the user's own most recently used first - the order texture_library() produced); a user tile
-    // carries a remove button on hover. Returns how many it drew.
+    // carries a remove button on hover. Returns how many tiles it laid out, drawn or not.
     const auto grid = [&](const ImVec2 &origin, const std::vector<const TextureLibraryEntry *> &entries, bool removable) {
         int n = 0;
         for (const TextureLibraryEntry *entry : entries) {
-            ImGui::SetCursorScreenPos(tile_pos(origin, n++));
+            const ImVec2 rect_min = tile_pos(origin, n++);
+            const ImVec2 rect_max = ImVec2(rect_min.x + tile, rect_min.y + tile);
+            const bool   current  = entry->path == layer->path;
+            // The selected tile is centred even when it is off screen, so it is drawn and loaded next frame.
+            if (current && m_picker_reveal_selected) {
+                ImGui::SetScrollFromPosY(0.5f * (rect_min.y + rect_max.y) - ImGui::GetWindowPos().y, 0.5f);
+                m_parent.set_as_dirty();
+            }
+            if (!ImGui::IsRectVisible(rect_min, rect_max))
+                continue;
+            // Thumbnails decode on this thread, so only a few per frame; the rest fill in on later frames.
+            const bool cached = m_library_textures.count(entry->path) != 0;
+            if (!cached && loads_left == 0) {
+                loads_deferred = true;
+                dl->AddRectFilled(rect_min, rect_max, ImGui::GetColorU32(ImGuiCol_FrameBg), style.FrameRounding);
+                continue;
+            }
+            if (!cached)
+                --loads_left;
+            ImGui::SetCursorScreenPos(rect_min);
             ImGui::PushID(entry->path.c_str());
             const LibraryTexture *tex     = get_library_texture(entry->path);
             GLTexture            *thumb   = tex != nullptr ? tex->thumbnail.get() : nullptr;
@@ -4375,7 +4400,6 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
             if (removable)
                 ImGui::SetItemAllowOverlap(); // the remove button drawn over its corner takes its own clicks
             const ImVec2 a       = ImGui::GetItemRectMin(), b = ImGui::GetItemRectMax();
-            const bool   current = entry->path == layer->path;
             const bool   hovered = ImGui::IsItemHovered();
             // The layer's current texture carries an accent ring, and the tile under the pointer a thinner,
             // fainter one. Both are drawn inside the tile, where the grid's clip rect never cuts them.
@@ -4384,9 +4408,6 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
                 dl->AddRect(ImVec2(a.x + 0.5f * w, a.y + 0.5f * w), ImVec2(b.x - 0.5f * w, b.y - 0.5f * w),
                             ImGui::GetColorU32(current ? orca : ImVec4(orca.x, orca.y, orca.z, 0.6f)), 0.f, 0, w);
             }
-            // Centred, as far as the scroll range allows, so the textures around it are in view too.
-            if (current && m_picker_reveal_selected)
-                ImGui::SetScrollFromPosY(0.5f * (a.y + b.y) - ImGui::GetWindowPos().y, 0.5f);
             if (hovered)
                 panel_tooltip(entry->name);
 
@@ -4575,6 +4596,8 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
         ImGui::TextDisabled("%s", _u8L("PNG, JPG or BMP - converted to a height map on import. Hover one of yours to remove it.").c_str());
         ImGui::PopTextWrapPos();
     }
+    if (loads_deferred)
+        m_parent.set_as_dirty();
     // Done whether or not the current texture was drawn: one in a collapsed section stays where it is.
     m_picker_reveal_selected = false;
     ImGui::EndChild();

src/slic3r/GUI/TextureLibrary.cpp

@@ -223,23 +223,11 @@ std::vector<unsigned char> read_file_bytes(const std::string &path)
     return std::vector<unsigned char>(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());
 }
 
-// True if these bytes are a PNG libslic3r can decode, i.e. can be stored on a layer as-is. Mirrors
-// exactly what decode_height_texture() accepts: 8-bit grayscale, or 8-bit colour (whose luminance is
-// the height and whose RGB is available to colour the model). Anything else is converted on load.
+// True if decode_height_texture() can read these bytes, so they can be stored on a layer as-is.
+// Anything else is converted on load.
 bool is_supported_height_map(const std::vector<unsigned char> &bytes)
 {
-    if (bytes.empty())
-        return false;
-    const png::ReadBuf rbuf{ bytes.data(), bytes.size() };
-    if (!png::is_png(rbuf))
-        return false;
-    png::ImageGreyscale gray;
-    if (png::decode_png(rbuf, gray) && gray.cols > 0 && gray.rows > 0)
-        return true;
-    png::ImageColorscale color;
-    return png::decode_colored_png(rbuf, color) && color.cols > 0 && color.rows > 0 &&
-           color.bytes_per_pixel >= 3 &&
-           color.buf.size() == color.cols * color.rows * size_t(color.bytes_per_pixel);
+    return !bytes.empty() && png::is_decodable_8bit_png(png::ReadBuf{ bytes.data(), bytes.size() });
 }
 
 std::vector<TextureLibraryEntry> g_library;