ImGuiIntegration: use single-channel format for font texture atlas, if available

src/Magnum/ImGuiIntegration/Context.cpp

@@ -38,6 +38,7 @@
 #include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Resource.h>
 #include <Magnum/ImageView.h>
+#include <Magnum/PixelFormat.h>
 #include <Magnum/GL/Context.h>
 #include <Magnum/GL/DefaultFramebuffer.h>
 #include <Magnum/GL/Extensions.h>
@@ -196,27 +197,45 @@ 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;
-        io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height, &pixelSize);
-        CORRADE_INTERNAL_ASSERT(width > 0 && height > 0 && pixelSize == 4);
+        /* 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)
+        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));
 
-        ImageView2D image{GL::PixelFormat::RGBA,
-            GL::PixelType::UnsignedByte, {width, height},
+        /* Atlas width is guaranteed to be a power-of-two, so the default
+           PixelStorage works even for the single-channel format */
+        const ImageView2D image{format, {width, height},
             {pixels, std::size_t(pixelSize*width*height)}};
 
         _texture = GL::Texture2D{};
         _texture.setMagnificationFilter(GL::SamplerFilter::Linear)
             .setMinificationFilter(GL::SamplerFilter::Linear)
             #ifndef MAGNUM_TARGET_GLES2
-            .setStorage(1, GL::TextureFormat::RGBA8, image.size())
+            .setStorage(1, GL::textureFormat(format), image.size())
             .setSubImage(0, {}, image)
             #else
-            .setImage(0, GL::TextureFormat::RGBA, image)
+            .setImage(0, GL::textureFormat(format), image)
             #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

@@ -5,7 +5,7 @@
 #               2020, 2021, 2022, 2023, 2024
 #             Vladimír Vondruš <[email protected]>
 #   Copyright © 2018 Jonathan Hale <[email protected]>
-#   Copyright © 2022 Pablo Escobar <[email protected]>
+#   Copyright © 2022, 2024 Pablo Escobar <[email protected]>
 #
 #   Permission is hereby granted, free of charge, to any person obtaining a
 #   copy of this software and associated documentation files (the "Software"),
@@ -63,6 +63,8 @@ if(MAGNUM_BUILD_GL_TESTS)
             ContextTestFiles/draw.png
             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

@@ -268,6 +268,8 @@ struct ContextGLTest: GL::OpenGLTester {
     void draw();
     void drawCallback();
     void drawTexture();
+    void drawText();
+    void drawTextColorFont();
     void drawScissor();
     void drawVertexOffset();
     void drawIndexOffset();
@@ -313,6 +315,8 @@ ContextGLTest::ContextGLTest() {
     addTests({&ContextGLTest::draw,
               &ContextGLTest::drawCallback,
               &ContextGLTest::drawTexture,
+              &ContextGLTest::drawText,
+              &ContextGLTest::drawTextColorFont,
               &ContextGLTest::drawScissor,
               &ContextGLTest::drawVertexOffset,
               &ContextGLTest::drawIndexOffset},
@@ -1397,6 +1401,127 @@ void ContextGLTest::drawTexture() {
         (DebugTools::CompareImageToFile{_manager, 1.0f, 0.5f}));
 }
 
+void ContextGLTest::drawText() {
+    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;
+
+    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));
+    drawList->AddText(nullptr, font->FontSize*font->Scale,
+        {size.x*0.3f, size.y*0.3f}, IM_COL32(255, 255, 0, 200), "ABC");
+
+    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.png"),
+        (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 */
+
+    /* In ImGui < 1.90, font->ConfigData is not set until calling Build() */
+    const float glyphSize = ImGui::GetIO().Fonts->ConfigData[0].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()};
 

src/Magnum/ImGuiIntegration/Widgets.h

@@ -58,7 +58,7 @@ inline ImTextureID textureId(GL::Texture2D& texture) {
     #if IMGUI_VERSION_NUM >= 19131
     return texture.id();
     #else
-    return reinterpret_cast<ImTextureID>(texture.id());
+    return reinterpret_cast<ImTextureID>(std::uintptr_t(texture.id()));
     #endif
 }