Backends: WGPU: added ImGuiBackendFlags_RendererHasTextures support. (#8465)

Author: ocornut

backends/imgui_impl_wgpu.cpp

@@ -6,8 +6,7 @@
 //  [X] Renderer: User texture binding. Use 'WGPUTextureView' as ImTextureID. Read the FAQ about ImTextureID/ImTextureRef!
 //  [X] Renderer: Large meshes support (64k+ vertices) even with 16-bit indices (ImGuiBackendFlags_RendererHasVtxOffset).
 //  [X] Renderer: Expose selected render state for draw callbacks to use. Access in '(ImGui_ImplXXXX_RenderState*)GetPlatformIO().Renderer_RenderState'.
-// Missing features or Issues:
-//  [ ] Renderer: Missing texture updates support for dynamic font atlas (ImGuiBackendFlags_RendererHasTextures).
+//  [X] Renderer: Texture updates support for dynamic font system (ImGuiBackendFlags_RendererHasTextures).
 
 // You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
 // Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
@@ -19,6 +18,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2025-06-12: Added support for ImGuiBackendFlags_RendererHasTextures, for dynamic font atlas. (#8465)
 //  2025-02-26: Recreate image bind groups during render. (#8426, #8046, #7765, #8027) + Update for latest webgpu-native changes.
 //  2024-10-14: Update Dawn support for change of string usages. (#8082, #8083)
 //  2024-10-07: Expose selected render state in ImGui_ImplWGPU_RenderState, which you can access in 'void* platform_io.Renderer_RenderState' during draw callbacks.
@@ -73,11 +73,15 @@ extern ImGuiID ImHashData(const void* data_p, size_t data_size, ImU32 seed);
 #define MEMALIGN(_SIZE,_ALIGN)        (((_SIZE) + ((_ALIGN) - 1)) & ~((_ALIGN) - 1))    // Memory align (copied from IM_ALIGN() macro).
 
 // WebGPU data
+struct ImGui_ImplWGPU_Texture
+{
+    WGPUTexture         Texture = nullptr;
+    WGPUTextureView     TextureView = nullptr;
+};
+
 struct RenderResources
 {
-    WGPUTexture         FontTexture = nullptr;          // Font texture
-    WGPUTextureView     FontTextureView = nullptr;      // Texture view for font texture
-    WGPUSampler         Sampler = nullptr;              // Sampler for the font texture
+    WGPUSampler         Sampler = nullptr;              // Sampler for textures
     WGPUBuffer          Uniforms = nullptr;             // Shader uniforms
     WGPUBindGroup       CommonBindGroup = nullptr;      // Resources bind-group to bind the common resources to pipeline
     ImGuiStorage        ImageBindGroups;                // Resources bind-group to bind the font/image resources to pipeline (this is a key->value map)
@@ -234,23 +238,8 @@ static void SafeRelease(WGPUShaderModule& res)
         wgpuShaderModuleRelease(res);
     res = nullptr;
 }
-static void SafeRelease(WGPUTextureView& res)
-{
-    if (res)
-        wgpuTextureViewRelease(res);
-    res = nullptr;
-}
-static void SafeRelease(WGPUTexture& res)
-{
-    if (res)
-        wgpuTextureRelease(res);
-    res = nullptr;
-}
-
 static void SafeRelease(RenderResources& res)
 {
-    SafeRelease(res.FontTexture);
-    SafeRelease(res.FontTextureView);
     SafeRelease(res.Sampler);
     SafeRelease(res.Uniforms);
     SafeRelease(res.CommonBindGroup);
@@ -381,6 +370,13 @@ void ImGui_ImplWGPU_RenderDrawData(ImDrawData* draw_data, WGPURenderPassEncoder
     if (fb_width <= 0 || fb_height <= 0 || draw_data->CmdListsCount == 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_ImplWGPU_UpdateTexture(tex);
+
     // FIXME: Assuming that this only gets called once per frame!
     // If not, we can't just re-allocate the IB or VB, we'll have to do a proper allocator.
     ImGui_ImplWGPU_Data* bd = ImGui_ImplWGPU_GetBackendData();
@@ -536,33 +532,52 @@ void ImGui_ImplWGPU_RenderDrawData(ImDrawData* draw_data, WGPURenderPassEncoder
     platform_io.Renderer_RenderState = nullptr;
 }
 
-static void ImGui_ImplWGPU_CreateFontsTexture()
+static void ImGui_ImplWGPU_DestroyTexture(ImTextureData* tex)
 {
-    // Build texture atlas
-    ImGui_ImplWGPU_Data* bd = ImGui_ImplWGPU_GetBackendData();
-    ImGuiIO& io = ImGui::GetIO();
-    unsigned char* pixels;
-    int width, height, size_pp;
-    io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height, &size_pp);
+    ImGui_ImplWGPU_Texture* backend_tex = (ImGui_ImplWGPU_Texture*)tex->BackendUserData;
+    if (backend_tex == nullptr)
+        return;
 
-    // Upload texture to graphics system
+    IM_ASSERT(backend_tex->TextureView == (WGPUTextureView)(intptr_t)tex->TexID);
+    wgpuTextureViewRelease(backend_tex->TextureView);
+    wgpuTextureRelease(backend_tex->Texture);
+    IM_DELETE(backend_tex);
+
+    // Clear identifiers and mark as destroyed (in order to allow e.g. calling InvalidateDeviceObjects while running)
+    tex->SetTexID(ImTextureID_Invalid);
+    tex->SetStatus(ImTextureStatus_Destroyed);
+    tex->BackendUserData = nullptr;
+}
+
+void ImGui_ImplWGPU_UpdateTexture(ImTextureData* tex)
+{
+    ImGui_ImplWGPU_Data* bd = ImGui_ImplWGPU_GetBackendData();
+    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 == ImTextureID_Invalid && tex->BackendUserData == nullptr);
+        IM_ASSERT(tex->Format == ImTextureFormat_RGBA32);
+        ImGui_ImplWGPU_Texture* backend_tex = IM_NEW(ImGui_ImplWGPU_Texture)();
+
+        // Create texture
         WGPUTextureDescriptor tex_desc = {};
 #if defined(IMGUI_IMPL_WEBGPU_BACKEND_DAWN) || defined(IMGUI_IMPL_WEBGPU_BACKEND_WGPU)
-        tex_desc.label = { "Dear ImGui Font Texture", WGPU_STRLEN };
+        tex_desc.label = { "Dear ImGui Texture", WGPU_STRLEN };
 #else
-        tex_desc.label = "Dear ImGui Font Texture";
+        tex_desc.label = "Dear ImGui Texture";
 #endif
         tex_desc.dimension = WGPUTextureDimension_2D;
-        tex_desc.size.width = width;
-        tex_desc.size.height = height;
+        tex_desc.size.width = tex->Width;
+        tex_desc.size.height = tex->Height;
         tex_desc.size.depthOrArrayLayers = 1;
         tex_desc.sampleCount = 1;
         tex_desc.format = WGPUTextureFormat_RGBA8Unorm;
         tex_desc.mipLevelCount = 1;
         tex_desc.usage = WGPUTextureUsage_CopyDst | WGPUTextureUsage_TextureBinding;
-        bd->renderResources.FontTexture = wgpuDeviceCreateTexture(bd->wgpuDevice, &tex_desc);
+        backend_tex->Texture = wgpuDeviceCreateTexture(bd->wgpuDevice, &tex_desc);
 
+        // Create texture view
         WGPUTextureViewDescriptor tex_view_desc = {};
         tex_view_desc.format = WGPUTextureFormat_RGBA8Unorm;
         tex_view_desc.dimension = WGPUTextureViewDimension_2D;
@@ -571,35 +586,50 @@ static void ImGui_ImplWGPU_CreateFontsTexture()
         tex_view_desc.baseArrayLayer = 0;
         tex_view_desc.arrayLayerCount = 1;
         tex_view_desc.aspect = WGPUTextureAspect_All;
-        bd->renderResources.FontTextureView = wgpuTextureCreateView(bd->renderResources.FontTexture, &tex_view_desc);
+        backend_tex->TextureView = wgpuTextureCreateView(backend_tex->Texture, &tex_view_desc);
+
+        // Store identifiers
+        tex->SetTexID((ImTextureID)(intptr_t)backend_tex->TextureView);
+        tex->BackendUserData = backend_tex;
+        // We don't set tex->Status to ImTextureStatus_OK to let the code fallthrough below.
     }
 
-    // Upload texture data
+    if (tex->Status == ImTextureStatus_WantCreate || tex->Status == ImTextureStatus_WantUpdates)
     {
+        ImGui_ImplWGPU_Texture* backend_tex = (ImGui_ImplWGPU_Texture*)tex->BackendUserData;
+        IM_ASSERT(tex->Format == ImTextureFormat_RGBA32);
+
+        // We could use the smaller rect on _WantCreate but using the full rect allows us to clear the texture.
+        const int upload_x = (tex->Status == ImTextureStatus_WantCreate) ? 0 : tex->UpdateRect.x;
+        const int upload_y = (tex->Status == ImTextureStatus_WantCreate) ? 0 : tex->UpdateRect.y;
+        const int upload_w = (tex->Status == ImTextureStatus_WantCreate) ? tex->Width : tex->UpdateRect.w;
+        const int upload_h = (tex->Status == ImTextureStatus_WantCreate) ? tex->Height : tex->UpdateRect.h;
+
+        // Update full texture or selected blocks. We only ever write to textures regions which have never been used before!
+        // This backend choose to use tex->UpdateRect but you can use tex->Updates[] to upload individual regions.
 #if defined(IMGUI_IMPL_WEBGPU_BACKEND_DAWN) || defined(IMGUI_IMPL_WEBGPU_BACKEND_WGPU)
         WGPUTexelCopyTextureInfo dst_view = {};
 #else
         WGPUImageCopyTexture dst_view = {};
 #endif
-        dst_view.texture = bd->renderResources.FontTexture;
+        dst_view.texture = backend_tex->Texture;
         dst_view.mipLevel = 0;
-        dst_view.origin = { 0, 0, 0 };
+        dst_view.origin = { (uint32_t)upload_x, (uint32_t)upload_y, 0 };
         dst_view.aspect = WGPUTextureAspect_All;
 #if defined(IMGUI_IMPL_WEBGPU_BACKEND_DAWN) || defined(IMGUI_IMPL_WEBGPU_BACKEND_WGPU)
         WGPUTexelCopyBufferLayout layout = {};
 #else
         WGPUTextureDataLayout layout = {};
 #endif
         layout.offset = 0;
-        layout.bytesPerRow = width * size_pp;
-        layout.rowsPerImage = height;
-        WGPUExtent3D size = { (uint32_t)width, (uint32_t)height, 1 };
-        wgpuQueueWriteTexture(bd->defaultQueue, &dst_view, pixels, (uint32_t)(width * size_pp * height), &layout, &size);
+        layout.bytesPerRow = tex->Width * tex->BytesPerPixel;
+        layout.rowsPerImage = upload_h;
+        WGPUExtent3D write_size = { (uint32_t)upload_w, (uint32_t)upload_h, 1 };
+        wgpuQueueWriteTexture(bd->defaultQueue, &dst_view, tex->GetPixelsAt(upload_x, upload_y), (uint32_t)(tex->Width * upload_h * tex->BytesPerPixel), &layout, &write_size);
+        tex->SetStatus(ImTextureStatus_OK);
     }
-
-    // Store our identifier
-    static_assert(sizeof(ImTextureID) >= sizeof(bd->renderResources.FontTexture), "Can't pack descriptor handle into TexID, 32-bit not supported yet.");
-    io.Fonts->SetTexID((ImTextureID)bd->renderResources.FontTextureView);
+    if (tex->Status == ImTextureStatus_WantDestroy && tex->UnusedFrames > 0)
+        ImGui_ImplWGPU_DestroyTexture(tex);
 }
 
 static void ImGui_ImplWGPU_CreateUniformBuffer()
@@ -743,7 +773,6 @@ bool ImGui_ImplWGPU_CreateDeviceObjects()
 
     bd->pipelineState = wgpuDeviceCreateRenderPipeline(bd->wgpuDevice, &graphics_pipeline_desc);
 
-    ImGui_ImplWGPU_CreateFontsTexture();
     ImGui_ImplWGPU_CreateUniformBuffer();
 
     // Create sampler
@@ -788,8 +817,10 @@ void ImGui_ImplWGPU_InvalidateDeviceObjects()
     SafeRelease(bd->pipelineState);
     SafeRelease(bd->renderResources);
 
-    ImGuiIO& io = ImGui::GetIO();
-    io.Fonts->SetTexID(0); // We copied g_pFontTextureView to io.Fonts->TexID so let's clear that as well.
+    // Destroy all textures
+    for (ImTextureData* tex : ImGui::GetPlatformIO().Textures)
+        if (tex->RefCount == 1)
+            ImGui_ImplWGPU_DestroyTexture(tex);
 
     for (unsigned int i = 0; i < bd->numFramesInFlight; i++)
         SafeRelease(bd->pFrameResources[i]);
@@ -814,6 +845,7 @@ bool ImGui_ImplWGPU_Init(ImGui_ImplWGPU_InitInfo* init_info)
     io.BackendRendererName = "imgui_impl_webgpu";
 #endif
     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->initInfo = *init_info;
     bd->wgpuDevice = init_info->Device;
@@ -823,8 +855,6 @@ bool ImGui_ImplWGPU_Init(ImGui_ImplWGPU_InitInfo* init_info)
     bd->numFramesInFlight = init_info->NumFramesInFlight;
     bd->frameIndex = UINT_MAX;
 
-    bd->renderResources.FontTexture = nullptr;
-    bd->renderResources.FontTextureView = nullptr;
     bd->renderResources.Sampler = nullptr;
     bd->renderResources.Uniforms = nullptr;
     bd->renderResources.CommonBindGroup = nullptr;
@@ -863,7 +893,7 @@ void ImGui_ImplWGPU_Shutdown()
 
     io.BackendRendererName = nullptr;
     io.BackendRendererUserData = nullptr;
-    io.BackendFlags &= ~ImGuiBackendFlags_RendererHasVtxOffset;
+    io.BackendFlags &= ~(ImGuiBackendFlags_RendererHasVtxOffset | ImGuiBackendFlags_RendererHasTextures);
     IM_DELETE(bd);
 }
 

backends/imgui_impl_wgpu.h

@@ -13,8 +13,7 @@
 //  [X] Renderer: User texture binding. Use 'WGPUTextureView' as ImTextureID. Read the FAQ about ImTextureID/ImTextureRef!
 //  [X] Renderer: Large meshes support (64k+ vertices) even with 16-bit indices (ImGuiBackendFlags_RendererHasVtxOffset).
 //  [X] Renderer: Expose selected render state for draw callbacks to use. Access in '(ImGui_ImplXXXX_RenderState*)GetPlatformIO().Renderer_RenderState'.
-// Missing features or Issues:
-//  [ ] Renderer: Missing texture updates support for dynamic font atlas (ImGuiBackendFlags_RendererHasTextures).
+//  [X] Renderer: Texture updates support for dynamic font system (ImGuiBackendFlags_RendererHasTextures).
 
 // You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
 // Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
@@ -57,6 +56,9 @@ IMGUI_IMPL_API void ImGui_ImplWGPU_RenderDrawData(ImDrawData* draw_data, WGPURen
 IMGUI_IMPL_API bool ImGui_ImplWGPU_CreateDeviceObjects();
 IMGUI_IMPL_API void ImGui_ImplWGPU_InvalidateDeviceObjects();
 
+// (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_ImplWGPU_UpdateTexture(ImTextureData* tex);
+
 // [BETA] Selected render state data shared with callbacks.
 // This is temporarily stored in GetPlatformIO().Renderer_RenderState during the ImGui_ImplWGPU_RenderDrawData() call.
 // (Please open an issue if you feel you need access to more data)

docs/CHANGELOG.txt

@@ -363,7 +363,7 @@ Other changes:
 - Misc: added extra operators to ImVec4 in IMGUI_DEFINE_MATH_OPERATORS block. (#8510) [@gan74]
 - Demo: changed default framed item width to use Min(GetFontSize() * 12, GetContentRegionAvail().x * 0.40f).
 - Backends:
-  - Backends: DX9/DX10/DX11/DX12, Vulkan, OpenGL2/3, Metal, SDLGPU3, SDLRenderer2/3, Allegro5:
+  - Backends: DX9/DX10/DX11/DX12, Vulkan, OpenGL2/3, Metal, SDLGPU3, SDLRenderer2/3, WebGPU, Allegro5:
     - Added ImGuiBackendFlags_RendererHasTextures support. (#8465, #3761, #3471)
       [@ocornut, @ShironekoBen, @thedmd]
     - Added ImGui_ImplXXXX_UpdateTexture(ImTextureData* tex) functions for all backend.