Backends: SDL_Renderer3: added ImGuiBackendFlags_RendererHasTextures support.

Author: ocornut

backends/imgui_impl_sdlrenderer3.cpp

@@ -10,8 +10,9 @@
 // and it might be difficult to step out of those boundaries.
 
 // Implemented features:
-//  [X] Renderer: User texture binding. Use 'SDL_Texture*' as ImTextureID. Read the FAQ about ImTextureID!
+//  [X] Renderer: User texture binding. Use 'SDL_Texture*' as texture identifier. Read the FAQ about ImTextureID/ImTextureRef!
 //  [X] Renderer: Large meshes support (64k+ vertices) even with 16-bit indices (ImGuiBackendFlags_RendererHasVtxOffset).
+//  [X] Renderer: Texture updates support for dynamic font system (ImGuiBackendFlags_RendererHasTextures).
 //  [X] Renderer: Expose selected render state for draw callbacks to use. Access in '(ImGui_ImplXXXX_RenderState*)GetPlatformIO().Renderer_RenderState'.
 
 // You can copy and use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
@@ -23,6 +24,7 @@
 // - Introduction, links and more at the top of imgui.cpp
 
 // CHANGELOG
+//  2025-06-11: Added support for ImGuiBackendFlags_RendererHasTextures, for dynamic font atlas. Removed ImGui_ImplSDLRenderer3_CreateFontsTexture() and ImGui_ImplSDLRenderer3_DestroyFontsTexture().
 //  2025-01-18: Use endian-dependent RGBA32 texture format, to match SDL_Color.
 //  2024-10-09: Expose selected render state in ImGui_ImplSDLRenderer3_RenderState, which you can access in 'void* platform_io.Renderer_RenderState' during draw callbacks.
 //  2024-07-01: Update for SDL3 api changes: SDL_RenderGeometryRaw() uint32 version was removed (SDL#9009).
@@ -51,7 +53,6 @@
 struct ImGui_ImplSDLRenderer3_Data
 {
     SDL_Renderer*           Renderer;       // Main viewport's renderer
-    SDL_Texture*            FontTexture;
     ImVector<SDL_FColor>    ColorBuffer;
 
     ImGui_ImplSDLRenderer3_Data()   { memset((void*)this, 0, sizeof(*this)); }
@@ -77,6 +78,7 @@ bool ImGui_ImplSDLRenderer3_Init(SDL_Renderer* renderer)
     io.BackendRendererUserData = (void*)bd;
     io.BackendRendererName = "imgui_impl_sdlrenderer3";
     io.BackendFlags |= ImGuiBackendFlags_RendererHasVtxOffset;  // We can honor the ImDrawCmd::VtxOffset field, allowing for large meshes.
+    io.BackendFlags |= ImGuiBackendFlags_RendererHasTextures;   // We can honor ImGuiPlatformIO::Textures[] requests during render.
 
     bd->Renderer = renderer;
 
@@ -93,7 +95,7 @@ void ImGui_ImplSDLRenderer3_Shutdown()
 
     io.BackendRendererName = nullptr;
     io.BackendRendererUserData = nullptr;
-    io.BackendFlags &= ~ImGuiBackendFlags_RendererHasVtxOffset;
+    io.BackendFlags &= ~(ImGuiBackendFlags_RendererHasVtxOffset | ImGuiBackendFlags_RendererHasTextures);
     IM_DELETE(bd);
 }
 
@@ -109,9 +111,7 @@ void ImGui_ImplSDLRenderer3_NewFrame()
 {
     ImGui_ImplSDLRenderer3_Data* bd = ImGui_ImplSDLRenderer3_GetBackendData();
     IM_ASSERT(bd != nullptr && "Context or backend not initialized! Did you call ImGui_ImplSDLRenderer3_Init()?");
-
-    if (!bd->FontTexture)
-        ImGui_ImplSDLRenderer3_CreateDeviceObjects();
+    IM_UNUSED(bd);
 }
 
 // https://github.com/libsdl-org/SDL/issues/9009
@@ -152,6 +152,13 @@ void ImGui_ImplSDLRenderer3_RenderDrawData(ImDrawData* draw_data, SDL_Renderer*
     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_ImplSDLRenderer3_UpdateTexture(tex);
+
     // Backup SDL_Renderer state that will be modified to restore it afterwards
     struct BackupSDLRendererState
     {
@@ -235,55 +242,67 @@ void ImGui_ImplSDLRenderer3_RenderDrawData(ImDrawData* draw_data, SDL_Renderer*
     SDL_SetRenderClipRect(renderer, old.ClipEnabled ? &old.ClipRect : nullptr);
 }
 
-// Called by Init/NewFrame/Shutdown
-bool ImGui_ImplSDLRenderer3_CreateFontsTexture()
+void ImGui_ImplSDLRenderer3_UpdateTexture(ImTextureData* tex)
 {
-    ImGuiIO& io = ImGui::GetIO();
     ImGui_ImplSDLRenderer3_Data* bd = ImGui_ImplSDLRenderer3_GetBackendData();
 
-    // Build texture atlas
-    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)
-    bd->FontTexture = SDL_CreateTexture(bd->Renderer, SDL_PIXELFORMAT_RGBA32, SDL_TEXTUREACCESS_STATIC, width, height);
-    if (bd->FontTexture == nullptr)
+    if (tex->Status == ImTextureStatus_WantCreate)
     {
-        SDL_Log("error creating texture");
-        return false;
+        // 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);
+
+        // Create texture
+        // (Bilinear sampling is required by default. Set 'io.Fonts->Flags |= ImFontAtlasFlags_NoBakedLines' or 'style.AntiAliasedLinesUseTex = false' to allow point/nearest sampling)
+        SDL_Texture* sdl_texture = SDL_CreateTexture(bd->Renderer, SDL_PIXELFORMAT_RGBA32, SDL_TEXTUREACCESS_STATIC, tex->Width, tex->Height);
+        IM_ASSERT(sdl_texture != nullptr && "Backend failed to create texture!");
+        SDL_UpdateTexture(sdl_texture, nullptr, tex->GetPixels(), tex->GetPitch());
+        SDL_SetTextureBlendMode(sdl_texture, SDL_BLENDMODE_BLEND);
+        SDL_SetTextureScaleMode(sdl_texture, SDL_SCALEMODE_LINEAR);
+
+        // Store identifiers
+        tex->SetTexID((ImTextureID)(intptr_t)sdl_texture);
+        tex->SetStatus(ImTextureStatus_OK);
     }
-    SDL_UpdateTexture(bd->FontTexture, nullptr, pixels, 4 * width);
-    SDL_SetTextureBlendMode(bd->FontTexture, SDL_BLENDMODE_BLEND);
-    SDL_SetTextureScaleMode(bd->FontTexture, SDL_SCALEMODE_LINEAR);
-
-    // Store our identifier
-    io.Fonts->SetTexID((ImTextureID)(intptr_t)bd->FontTexture);
-
-    return true;
-}
-
-void ImGui_ImplSDLRenderer3_DestroyFontsTexture()
-{
-    ImGuiIO& io = ImGui::GetIO();
-    ImGui_ImplSDLRenderer3_Data* bd = ImGui_ImplSDLRenderer3_GetBackendData();
-    if (bd->FontTexture)
+    else if (tex->Status == ImTextureStatus_WantUpdates)
     {
-        io.Fonts->SetTexID(0);
-        SDL_DestroyTexture(bd->FontTexture);
-        bd->FontTexture = nullptr;
+        // 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.
+        SDL_Texture* sdl_texture = (SDL_Texture*)(intptr_t)tex->TexID;
+        for (ImTextureRect& r : tex->Updates)
+        {
+            SDL_Rect sdl_r = { r.x, r.y, r.w, r.h };
+            SDL_UpdateTexture(sdl_texture, &sdl_r, tex->GetPixelsAt(r.x, r.y), tex->GetPitch());
+        }
+        tex->SetStatus(ImTextureStatus_OK);
+    }
+    else if (tex->Status == ImTextureStatus_WantDestroy)
+    {
+        SDL_Texture* sdl_texture = (SDL_Texture*)(intptr_t)tex->TexID;
+        if (sdl_texture == nullptr)
+            return;
+        SDL_DestroyTexture(sdl_texture);
+
+        // 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_ImplSDLRenderer3_CreateDeviceObjects()
+void ImGui_ImplSDLRenderer3_CreateDeviceObjects()
 {
-    return ImGui_ImplSDLRenderer3_CreateFontsTexture();
 }
 
 void ImGui_ImplSDLRenderer3_DestroyDeviceObjects()
 {
-    ImGui_ImplSDLRenderer3_DestroyFontsTexture();
+    // Destroy all textures
+    for (ImTextureData* tex : ImGui::GetPlatformIO().Textures)
+        if (tex->RefCount == 1)
+        {
+            tex->SetStatus(ImTextureStatus_WantDestroy);
+            ImGui_ImplSDLRenderer3_UpdateTexture(tex);
+        }
 }
 
 //-----------------------------------------------------------------------------

backends/imgui_impl_sdlrenderer3.h

@@ -10,8 +10,9 @@
 // and it might be difficult to step out of those boundaries.
 
 // Implemented features:
-//  [X] Renderer: User texture binding. Use 'SDL_Texture*' as ImTextureID. Read the FAQ about ImTextureID!
+//  [X] Renderer: User texture binding. Use 'SDL_Texture*' as texture identifier. Read the FAQ about ImTextureID/ImTextureRef!
 //  [X] Renderer: Large meshes support (64k+ vertices) even with 16-bit indices (ImGuiBackendFlags_RendererHasVtxOffset).
+//  [X] Renderer: Texture updates support for dynamic font system (ImGuiBackendFlags_RendererHasTextures).
 //  [X] Renderer: Expose selected render state for draw callbacks to use. Access in '(ImGui_ImplXXXX_RenderState*)GetPlatformIO().Renderer_RenderState'.
 
 // You can copy and use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
@@ -35,11 +36,12 @@ IMGUI_IMPL_API void     ImGui_ImplSDLRenderer3_NewFrame();
 IMGUI_IMPL_API void     ImGui_ImplSDLRenderer3_RenderDrawData(ImDrawData* draw_data, SDL_Renderer* renderer);
 
 // Called by Init/NewFrame/Shutdown
-IMGUI_IMPL_API bool     ImGui_ImplSDLRenderer3_CreateFontsTexture();
-IMGUI_IMPL_API void     ImGui_ImplSDLRenderer3_DestroyFontsTexture();
-IMGUI_IMPL_API bool     ImGui_ImplSDLRenderer3_CreateDeviceObjects();
+IMGUI_IMPL_API void     ImGui_ImplSDLRenderer3_CreateDeviceObjects();
 IMGUI_IMPL_API void     ImGui_ImplSDLRenderer3_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_ImplSDLRenderer3_UpdateTexture(ImTextureData* tex);
+
 // [BETA] Selected render state data shared with callbacks.
 // This is temporarily stored in GetPlatformIO().Renderer_RenderState during the ImGui_ImplSDLRenderer3_RenderDrawData() call.
 // (Please open an issue if you feel you need access to more data)