Backends: SDL_GPU: add swapchain parameters to ImGui_ImplSDLGPU3_InitInfo. (#8892)

(docking branch commit)

backends/imgui_impl_sdlgpu3.cpp

@@ -24,6 +24,7 @@
 
 // CHANGELOG
 //  2025-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
+//  2025-08-20: Added SwapchainComposition::SwapchainComposition and SwapchainComposition::PresentMode to configure how secondary viewports are created.
 //  2025-08-08: *BREAKING* Changed ImTextureID type from SDL_GPUTextureSamplerBinding* to SDL_GPUTexture*, which is more natural and easier for user to manage. If you need to change the current sampler, you can access the ImGui_ImplSDLGPU3_RenderState struct. (#8866, #8163, #7998, #7988)
 //  2025-08-08: Expose SamplerDefault and SamplerCurrent in ImGui_ImplSDLGPU3_RenderState. Allow callback to change sampler.
 //  2025-06-25: Mapping transfer buffer for texture update use cycle=true. Fixes artifacts e.g. on Metal backend.
@@ -677,6 +678,7 @@ static void ImGui_ImplSDLGPU3_CreateWindow(ImGuiViewport* viewport)
     ImGui_ImplSDLGPU3_Data* data = ImGui_ImplSDLGPU3_GetBackendData();
     SDL_Window* window = SDL_GetWindowFromID((SDL_WindowID)(intptr_t)viewport->PlatformHandle);
     SDL_ClaimWindowForGPUDevice(data->InitInfo.Device, window);
+    SDL_SetGPUSwapchainParameters(data->InitInfo.Device, window, data->InitInfo.SwapchainComposition, data->InitInfo.PresentMode);
     viewport->RendererUserData = (void*)1;
 }
 

backends/imgui_impl_sdlgpu3.h

@@ -28,12 +28,14 @@
 #include <SDL3/SDL_gpu.h>
 
 // Initialization data, for ImGui_ImplSDLGPU_Init()
-// - Remember to set ColorTargetFormat to the correct format. If you're rendering to the swapchain, call SDL_GetGPUSwapchainTextureFormat to query the right value
+// - Remember to set ColorTargetFormat to the correct format. If you're rendering to the swapchain, call SDL_GetGPUSwapchainTextureFormat() to query the right value
 struct ImGui_ImplSDLGPU3_InitInfo
 {
-    SDL_GPUDevice*       Device             = nullptr;
-    SDL_GPUTextureFormat ColorTargetFormat  = SDL_GPU_TEXTUREFORMAT_INVALID;
-    SDL_GPUSampleCount   MSAASamples        = SDL_GPU_SAMPLECOUNT_1;
+    SDL_GPUDevice*              Device                  = nullptr;
+    SDL_GPUTextureFormat        ColorTargetFormat       = SDL_GPU_TEXTUREFORMAT_INVALID;
+    SDL_GPUSampleCount          MSAASamples             = SDL_GPU_SAMPLECOUNT_1;
+    SDL_GPUSwapchainComposition SwapchainComposition    = SDL_GPU_SWAPCHAINCOMPOSITION_SDR;     // Only used in multi-viewports mode.
+    SDL_GPUPresentMode          PresentMode             = SDL_GPU_PRESENTMODE_VSYNC;            // Only used in multi-viewports mode.
 };
 
 // Follow "Getting Started" link and check examples/ folder to learn about using backends!

examples/example_sdl3_sdlgpu3/main.cpp

@@ -94,7 +94,9 @@ int main(int, char**)
     ImGui_ImplSDLGPU3_InitInfo init_info = {};
     init_info.Device = gpu_device;
     init_info.ColorTargetFormat = SDL_GetGPUSwapchainTextureFormat(gpu_device, window);
-    init_info.MSAASamples = SDL_GPU_SAMPLECOUNT_1;
+    init_info.MSAASamples = SDL_GPU_SAMPLECOUNT_1;                      // Only used in multi-viewports mode.
+    init_info.SwapchainComposition = SDL_GPU_SWAPCHAINCOMPOSITION_SDR;  // Only used in multi-viewports mode.
+    init_info.PresentMode = SDL_GPU_PRESENTMODE_VSYNC;
     ImGui_ImplSDLGPU3_Init(&init_info);
 
     // Load Fonts