ImGuiIntegration: use 4-channel font atlas texture format if it conta…

…ins color.

src/Magnum/ImGuiIntegration/Context.cpp

@@ -197,18 +197,22 @@ void Context::relayout(const Vector2& size, const Vector2i& windowSize, const Ve
         /* Downscale back the upscaled font to achieve supersampling */
         io.FontGlobalScale = 1.0f/nonZeroSupersamplingRatio;
 
+        PixelFormat format;
         unsigned char *pixels;
         int width, height;
         int pixelSize;
-        /* Texture atlas only requires alpha. Use a single-channel format and
-           swizzle, if available, to conserve memory. */
+        /* If the texture atlas only requires alpha we can use a single-channel
+           format and swizzle, if available, to conserve memory */
         #if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
-        constexpr PixelFormat format = PixelFormat::R8Unorm;
-        io.Fonts->GetTexDataAsAlpha8(&pixels, &width, &height, &pixelSize);
-        #else
-        constexpr PixelFormat format = PixelFormat::RGBA8Unorm;
-        io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height, &pixelSize);
+        if(!io.Fonts->TexPixelsUseColors) {
+            format = PixelFormat::R8Unorm;
+            io.Fonts->GetTexDataAsAlpha8(&pixels, &width, &height, &pixelSize);
+        } else
         #endif
+        {
+            format = PixelFormat::RGBA8Unorm;
+            io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height, &pixelSize);
+        }
         CORRADE_INTERNAL_ASSERT(width > 0 && height > 0 && std::size_t(pixelSize) == pixelFormatSize(format));
 
         /* Atlas width is guaranteed to be a power-of-two, so the default
@@ -225,11 +229,13 @@ void Context::relayout(const Vector2& size, const Vector2i& windowSize, const Ve
             #else
             .setImage(0, GL::textureFormat(format), image)
             #endif
-            #if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
-            .setSwizzle<'1', '1', '1', 'r'>()
-            #endif
             ;
 
+        #if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
+        if(!io.Fonts->TexPixelsUseColors)
+            _texture.setSwizzle<'1', '1', '1', 'r'>();
+        #endif
+
         /* Clear texture to save RAM, we have it on the GPU now */
         io.Fonts->ClearTexData();
 

src/Magnum/ImGuiIntegration/Test/CMakeLists.txt

@@ -64,6 +64,7 @@ if(MAGNUM_BUILD_GL_TESTS)
             ContextTestFiles/draw-scissor.png
             ContextTestFiles/draw-texture.png
             ContextTestFiles/draw-text.png
+            ContextTestFiles/draw-text-color-font.png
             ContextTestFiles/texture.png)
     target_include_directories(ImGuiContextGLTest PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
     if(MAGNUM_IMGUIINTEGRATION_BUILD_STATIC)

src/Magnum/ImGuiIntegration/Test/ContextGLTest.cpp

@@ -269,6 +269,7 @@ struct ContextGLTest: GL::OpenGLTester {
     void drawCallback();
     void drawTexture();
     void drawText();
+    void drawTextColorFont();
     void drawScissor();
     void drawVertexOffset();
     void drawIndexOffset();
@@ -315,6 +316,7 @@ ContextGLTest::ContextGLTest() {
               &ContextGLTest::drawCallback,
               &ContextGLTest::drawTexture,
               &ContextGLTest::drawText,
+              &ContextGLTest::drawTextColorFont,
               &ContextGLTest::drawScissor,
               &ContextGLTest::drawVertexOffset,
               &ContextGLTest::drawIndexOffset},
@@ -1409,6 +1411,8 @@ void ContextGLTest::drawText() {
 
     c.relayout({200, 200}, {70, 70}, _framebuffer.viewport().size());
 
+    MAGNUM_VERIFY_NO_GL_ERROR();
+
     /* ImGui doesn't draw anything the first frame */
     c.newFrame();
     c.drawFrame();
@@ -1444,6 +1448,78 @@ void ContextGLTest::drawText() {
         (DebugTools::CompareImageToFile{_manager, 3.0f, 0.5f}));
 }
 
+void ContextGLTest::drawTextColorFont() {
+    Context c{{200, 200}};
+
+    /* Scale up default font so large text output is not a complete blurry mess */
+    ImGui::GetIO().Fonts->Clear();
+    auto* font = ImGui::GetIO().Fonts->AddFontDefault();
+    font->Scale = 8.0f;
+
+    /* Add a custom glyph rect for Unicode black square (U+25A0) and color it */
+    const float glyphSize = font->ConfigData->SizePixels;
+    const int rectIndex = ImGui::GetIO().Fonts->AddCustomRectFontGlyph(font, L'\u25A0',
+        glyphSize*0.5f, glyphSize*0.5f, glyphSize, {glyphSize*0.25f, glyphSize*0.25f});
+    ImFontAtlasCustomRect* rect = ImGui::GetIO().Fonts->GetCustomRectByIndex(rectIndex);
+    /* Build the atlas manually so we get the offsets to draw to. drawText()
+       already checked that Build() is correctly called by relayout(). */
+    ImGui::GetIO().Fonts->Build();
+
+    unsigned char* pixelData;
+    int width;
+    int height;
+    ImGui::GetIO().Fonts->GetTexDataAsRGBA32(&pixelData, &width, &height);
+    Color4ub* pixels = reinterpret_cast<Color4ub*>(pixelData);
+    for(UnsignedShort y = rect->Y; y < rect->Y + rect->Height; ++y)
+        for(UnsignedShort x = rect->X; x < rect->X + rect->Width; ++x)
+            pixels[(y*width) + x] = Color4ub{128, 255, 128, 128};
+
+    /* Tell the backend that the font atlas contains colored glyphs so it
+       always creates an RGBA texture */
+    ImGui::GetIO().Fonts->TexPixelsUseColors = true;
+
+    c.relayout({200, 200}, {70, 70}, _framebuffer.viewport().size());
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
+
+    /* ImGui doesn't draw anything the first frame */
+    c.newFrame();
+    c.drawFrame();
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
+
+    Utility::System::sleep(1);
+
+    c.newFrame();
+
+    /* Last drawlist that gets rendered, covers the entire display */
+    ImDrawList* drawList = ImGui::GetForegroundDrawList();
+    const ImVec2& size = ImGui::GetIO().DisplaySize;
+
+    drawList->AddRectFilled({size.x*0.1f, size.y*0.2f}, {size.x*0.9f, size.y*0.8f},
+        IM_COL32(255, 128, 128, 255));
+    /* White, gets multiplied with the glyph color */
+    drawList->AddText(nullptr, font->FontSize*font->Scale,
+        {size.x*0.0f, size.y*0.0f}, IM_COL32(255, 255, 255, 255), u8"A\u25A0B");
+    drawList->AddText(nullptr, font->FontSize*font->Scale,
+        {size.x*0.0f, size.y*0.5f}, IM_COL32(255, 255, 255, 255), u8"\u25A0\u25A0");
+
+    c.drawFrame();
+
+    MAGNUM_VERIFY_NO_GL_ERROR();
+
+    /* Catch also ABI and interface mismatch errors */
+    if(!(_manager.load("AnyImageImporter") & PluginManager::LoadState::Loaded) ||
+       !(_manager.load("PngImporter") & PluginManager::LoadState::Loaded))
+        CORRADE_SKIP("AnyImageImporter / PngImporter plugin can't be loaded.");
+
+    CORRADE_COMPARE_WITH(
+        /* Dropping the alpha channel, as it's always 1.0 */
+        Containers::arrayCast<Color3ub>(_framebuffer.read(_framebuffer.viewport(), {PixelFormat::RGBA8Unorm}).pixels<Color4ub>()),
+        Utility::Path::join(IMGUIINTEGRATION_TEST_DIR, "ContextTestFiles/draw-text-color-font.png"),
+        (DebugTools::CompareImageToFile{_manager, 3.0f, 0.5f}));
+}
+
 void ContextGLTest::drawScissor() {
     Context c{{200, 200}, {70, 70}, _framebuffer.viewport().size()};