Backends: OpenGL2: added ImGuiBackendFlags_RendererHasTextures support.

Removed ImGui_ImplOpenGL2_CreateFontsTexture() and ImGui_ImplOpenGL2_DestroyFontsTexture().

backends/imgui_impl_opengl2.cpp

@@ -2,7 +2,8 @@
 // This needs to be used along with a Platform Backend (e.g. GLFW, SDL, Win32, custom..)
 
 // Implemented features:
-//  [X] Renderer: User texture binding. Use 'GLuint' OpenGL texture identifier as void*/ImTextureID. Read the FAQ about ImTextureID!
+//  [X] Renderer: User texture binding. Use 'GLuint' OpenGL texture as texture identifier. Read the FAQ about ImTextureID/ImTextureRef!
+//  [X] Renderer: Texture updates support for dynamic font system (ImGuiBackendFlags_RendererHasTextures).
 // Missing features or Issues:
 //  [ ] Renderer: Large meshes support (64k+ vertices) even with 16-bit indices (ImGuiBackendFlags_RendererHasVtxOffset).
 
@@ -24,6 +25,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2025-06-11: OpenGL: Added support for ImGuiBackendFlags_RendererHasTextures, for dynamic font atlas. Removed ImGui_ImplOpenGL2_CreateFontsTexture() and ImGui_ImplOpenGL2_DestroyFontsTexture().
 //  2024-10-07: OpenGL: Changed default texture sampler to Clamp instead of Repeat/Wrap.
 //  2024-06-28: OpenGL: ImGui_ImplOpenGL2_NewFrame() recreates font texture if it has been destroyed by ImGui_ImplOpenGL2_DestroyFontsTexture(). (#7748)
 //  2022-10-11: Using 'nullptr' instead of 'NULL' as per our switch to C++11.
@@ -81,8 +83,6 @@
 // OpenGL data
 struct ImGui_ImplOpenGL2_Data
 {
-    GLuint       FontTexture;
-
     ImGui_ImplOpenGL2_Data() { memset((void*)this, 0, sizeof(*this)); }
 };
 
@@ -104,6 +104,7 @@ bool    ImGui_ImplOpenGL2_Init()
     ImGui_ImplOpenGL2_Data* bd = IM_NEW(ImGui_ImplOpenGL2_Data)();
     io.BackendRendererUserData = (void*)bd;
     io.BackendRendererName = "imgui_impl_opengl2";
+    io.BackendFlags |= ImGuiBackendFlags_RendererHasTextures;       // We can honor ImGuiPlatformIO::Textures[] requests during render.
 
     return true;
 }
@@ -117,6 +118,7 @@ void    ImGui_ImplOpenGL2_Shutdown()
     ImGui_ImplOpenGL2_DestroyDeviceObjects();
     io.BackendRendererName = nullptr;
     io.BackendRendererUserData = nullptr;
+    io.BackendFlags &= ~(ImGuiBackendFlags_RendererHasTextures);
     IM_DELETE(bd);
 }
 
@@ -124,11 +126,7 @@ void    ImGui_ImplOpenGL2_NewFrame()
 {
     ImGui_ImplOpenGL2_Data* bd = ImGui_ImplOpenGL2_GetBackendData();
     IM_ASSERT(bd != nullptr && "Context or backend not initialized! Did you call ImGui_ImplOpenGL2_Init()?");
-
-    if (!bd->FontTexture)
-        ImGui_ImplOpenGL2_CreateDeviceObjects();
-    if (!bd->FontTexture)
-        ImGui_ImplOpenGL2_CreateFontsTexture();
+    IM_UNUSED(bd);
 }
 
 static void ImGui_ImplOpenGL2_SetupRenderState(ImDrawData* draw_data, int fb_width, int fb_height)
@@ -186,6 +184,13 @@ void ImGui_ImplOpenGL2_RenderDrawData(ImDrawData* draw_data)
     if (fb_width == 0 || fb_height == 0)
         return;
 
+    // Catch up with texture updates. Most of the times, the list will have 1 element with an OK status, aka nothing to do.
+    // (This almost always points to ImGui::GetPlatformIO().Textures[] but is part of ImDrawData to allow overriding or disabling texture updates).
+    if (draw_data->Textures != nullptr)
+        for (ImTextureData* tex : *draw_data->Textures)
+            if (tex->Status != ImTextureStatus_OK)
+                ImGui_ImplOpenGL2_UpdateTexture(tex);
+
     // Backup GL state
     GLint last_texture; glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
     GLint last_polygon_mode[2]; glGetIntegerv(GL_POLYGON_MODE, last_polygon_mode);
@@ -259,57 +264,77 @@ void ImGui_ImplOpenGL2_RenderDrawData(ImDrawData* draw_data)
     glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, last_tex_env_mode);
 }
 
-bool ImGui_ImplOpenGL2_CreateFontsTexture()
-{
-    // Build texture atlas
-    ImGuiIO& io = ImGui::GetIO();
-    ImGui_ImplOpenGL2_Data* bd = ImGui_ImplOpenGL2_GetBackendData();
-    unsigned char* pixels;
-    int width, height;
-    io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height);   // Load as RGBA 32-bit (75% of the memory is wasted, but default font is so small) because it is more likely to be compatible with user's existing shaders. If your ImTextureId represent a higher-level concept than just a GL texture id, consider calling GetTexDataAsAlpha8() instead to save on GPU memory.
-
-    // Upload texture to graphics system
-    // (Bilinear sampling is required by default. Set 'io.Fonts->Flags |= ImFontAtlasFlags_NoBakedLines' or 'style.AntiAliasedLinesUseTex = false' to allow point/nearest sampling)
-    GLint last_texture;
-    glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
-    glGenTextures(1, &bd->FontTexture);
-    glBindTexture(GL_TEXTURE_2D, bd->FontTexture);
-    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
-    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
-    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
-    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
-    glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
-    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
-
-    // Store our identifier
-    io.Fonts->SetTexID((ImTextureID)(intptr_t)bd->FontTexture);
-
-    // Restore state
-    glBindTexture(GL_TEXTURE_2D, last_texture);
-
-    return true;
-}
-
-void ImGui_ImplOpenGL2_DestroyFontsTexture()
+void ImGui_ImplOpenGL2_UpdateTexture(ImTextureData* tex)
 {
-    ImGuiIO& io = ImGui::GetIO();
-    ImGui_ImplOpenGL2_Data* bd = ImGui_ImplOpenGL2_GetBackendData();
-    if (bd->FontTexture)
+    if (tex->Status == ImTextureStatus_WantCreate)
+    {
+        // Create and upload new texture to graphics system
+        //IMGUI_DEBUG_LOG("UpdateTexture #%03d: WantCreate %dx%d\n", tex->UniqueID, tex->Width, tex->Height);
+        IM_ASSERT(tex->TexID == 0 && tex->BackendUserData == nullptr);
+        IM_ASSERT(tex->Format == ImTextureFormat_RGBA32);
+        const void* pixels = tex->GetPixels();
+        GLuint gl_texture_id = 0;
+
+        // Upload texture to graphics system
+        // (Bilinear sampling is required by default. Set 'io.Fonts->Flags |= ImFontAtlasFlags_NoBakedLines' or 'style.AntiAliasedLinesUseTex = false' to allow point/nearest sampling)
+        GLint last_texture;
+        GL_CALL(glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture));
+        GL_CALL(glGenTextures(1, &gl_texture_id));
+        GL_CALL(glBindTexture(GL_TEXTURE_2D, gl_texture_id));
+        GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR));
+        GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR));
+        GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP));
+        GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP));
+        GL_CALL(glPixelStorei(GL_UNPACK_ROW_LENGTH, 0));
+        GL_CALL(glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, tex->Width, tex->Height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels));
+
+        // Store identifiers
+        tex->SetTexID((ImTextureID)(intptr_t)gl_texture_id);
+        tex->SetStatus(ImTextureStatus_OK);
+
+        // Restore state
+        GL_CALL(glBindTexture(GL_TEXTURE_2D, last_texture));
+    }
+    else if (tex->Status == ImTextureStatus_WantUpdates)
+    {
+        // Update selected blocks. We only ever write to textures regions which have never been used before!
+        // This backend choose to use tex->Updates[] but you can use tex->UpdateRect to upload a single region.
+        GLint last_texture;
+        GL_CALL(glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture));
+
+        GLuint gl_tex_id = (GLuint)(intptr_t)tex->TexID;
+        GL_CALL(glBindTexture(GL_TEXTURE_2D, gl_tex_id));
+        GL_CALL(glPixelStorei(GL_UNPACK_ROW_LENGTH, tex->Width));
+        for (ImTextureRect& r : tex->Updates)
+            GL_CALL(glTexSubImage2D(GL_TEXTURE_2D, 0, r.x, r.y, r.w, r.h, GL_RGBA, GL_UNSIGNED_BYTE, tex->GetPixelsAt(r.x, r.y)));
+        GL_CALL(glPixelStorei(GL_UNPACK_ROW_LENGTH, 0));
+        GL_CALL(glBindTexture(GL_TEXTURE_2D, last_texture)); // Restore state
+        tex->SetStatus(ImTextureStatus_OK);
+    }
+    else if (tex->Status == ImTextureStatus_WantDestroy)
     {
-        glDeleteTextures(1, &bd->FontTexture);
-        io.Fonts->SetTexID(0);
-        bd->FontTexture = 0;
+        GLuint gl_tex_id = (GLuint)(intptr_t)tex->TexID;
+        glDeleteTextures(1, &gl_tex_id);
+
+        // Clear identifiers and mark as destroyed (in order to allow e.g. calling InvalidateDeviceObjects while running)
+        tex->SetTexID(ImTextureID_Invalid);
+        tex->SetStatus(ImTextureStatus_Destroyed);
     }
 }
 
 bool    ImGui_ImplOpenGL2_CreateDeviceObjects()
 {
-    return ImGui_ImplOpenGL2_CreateFontsTexture();
+    return true;
 }
 
 void    ImGui_ImplOpenGL2_DestroyDeviceObjects()
 {
-    ImGui_ImplOpenGL2_DestroyFontsTexture();
+    for (ImTextureData* tex : ImGui::GetPlatformIO().Textures)
+        if (tex->RefCount == 1)
+        {
+            tex->SetStatus(ImTextureStatus_WantDestroy);
+            ImGui_ImplOpenGL2_UpdateTexture(tex);
+        }
 }
 
 //-----------------------------------------------------------------------------

backends/imgui_impl_opengl2.h

@@ -2,7 +2,8 @@
 // This needs to be used along with a Platform Backend (e.g. GLFW, SDL, Win32, custom..)
 
 // Implemented features:
-//  [X] Renderer: User texture binding. Use 'GLuint' OpenGL texture identifier as void*/ImTextureID. Read the FAQ about ImTextureID!
+//  [X] Renderer: User texture binding. Use 'GLuint' OpenGL texture as texture identifier. Read the FAQ about ImTextureID/ImTextureRef!
+//  [X] Renderer: Texture updates support for dynamic font atlas (ImGuiBackendFlags_RendererHasTextures).
 // Missing features or Issues:
 //  [ ] Renderer: Large meshes support (64k+ vertices) even with 16-bit indices (ImGuiBackendFlags_RendererHasVtxOffset).
 
@@ -33,9 +34,10 @@ IMGUI_IMPL_API void     ImGui_ImplOpenGL2_NewFrame();
 IMGUI_IMPL_API void     ImGui_ImplOpenGL2_RenderDrawData(ImDrawData* draw_data);
 
 // Called by Init/NewFrame/Shutdown
-IMGUI_IMPL_API bool     ImGui_ImplOpenGL2_CreateFontsTexture();
-IMGUI_IMPL_API void     ImGui_ImplOpenGL2_DestroyFontsTexture();
 IMGUI_IMPL_API bool     ImGui_ImplOpenGL2_CreateDeviceObjects();
 IMGUI_IMPL_API void     ImGui_ImplOpenGL2_DestroyDeviceObjects();
 
+// (Advanced) Use e.g. if you need to precisely control the timing of texture updates (e.g. for staged rendering), by setting ImDrawData::Textures = NULL to handle this manually.
+IMGUI_IMPL_API void     ImGui_ImplOpenGL2_UpdateTexture(ImTextureData* tex);
+
 #endif // #ifndef IMGUI_DISABLE