Backends: DirectX12: reuse a command list and allocator for texture uploads. (#8963, #8465)

backends/imgui_impl_dx12.cpp

@@ -20,6 +20,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2025-09-27: DirectX12: Reuse a command list and allocator for texture uploads instead of recreating them each time.
 //  2025-09-18: Call platform_io.ClearRendererHandlers() on shutdown.
 //  2025-06-19: Fixed build on MinGW. (#8702, #4594)
 //  2025-06-11: DirectX12: Added support for ImGuiBackendFlags_RendererHasTextures, for dynamic font atlas.
@@ -97,6 +98,9 @@ struct ImGui_ImplDX12_Data
     ID3D12DescriptorHeap*       pd3dSrvDescHeap;
     UINT                        numFramesInFlight;
 
+    ID3D12CommandAllocator*     pTexCmdAllocator;
+    ID3D12GraphicsCommandList*  pTexCmdList;
+
     ImGui_ImplDX12_RenderBuffers* pFrameResources;
     UINT                        frameIndex;
 
@@ -448,13 +452,12 @@ void ImGui_ImplDX12_UpdateTexture(ImTextureData* tex)
         props.CPUPageProperty = D3D12_CPU_PAGE_PROPERTY_UNKNOWN;
         props.MemoryPoolPreference = D3D12_MEMORY_POOL_UNKNOWN;
 
-        // FIXME-OPT: Can upload buffer be reused?
+        // FIXME-OPT: Could upload buffer be kept around, reused, and grown only when needed? Would that be worth it?
         ID3D12Resource* uploadBuffer = nullptr;
         HRESULT hr = bd->pd3dDevice->CreateCommittedResource(&props, D3D12_HEAP_FLAG_NONE, &desc,
             D3D12_RESOURCE_STATE_GENERIC_READ, nullptr, IID_PPV_ARGS(&uploadBuffer));
         IM_ASSERT(SUCCEEDED(hr));
 
-        // Create temporary command list and execute immediately
         ID3D12Fence* fence = nullptr;
         hr = bd->pd3dDevice->CreateFence(0, D3D12_FENCE_FLAG_NONE, IID_PPV_ARGS(&fence));
         IM_ASSERT(SUCCEEDED(hr));
@@ -462,15 +465,9 @@ void ImGui_ImplDX12_UpdateTexture(ImTextureData* tex)
         HANDLE event = ::CreateEvent(0, 0, 0, 0);
         IM_ASSERT(event != nullptr);
 
-        // FIXME-OPT: Create once and reuse?
+        bd->pTexCmdAllocator->Reset();
-        ID3D12CommandAllocator* cmdAlloc = nullptr;
+        bd->pTexCmdList->Reset(bd->pTexCmdAllocator, nullptr);
-        hr = bd->pd3dDevice->CreateCommandAllocator(D3D12_COMMAND_LIST_TYPE_DIRECT, IID_PPV_ARGS(&cmdAlloc));
+        ID3D12GraphicsCommandList* cmdList = bd->pTexCmdList;
-        IM_ASSERT(SUCCEEDED(hr));
-
-        // FIXME-OPT: Can be use the one from user? (pass ID3D12GraphicsCommandList* to ImGui_ImplDX12_UpdateTextures)
-        ID3D12GraphicsCommandList* cmdList = nullptr;
-        hr = bd->pd3dDevice->CreateCommandList(0, D3D12_COMMAND_LIST_TYPE_DIRECT, cmdAlloc, nullptr, IID_PPV_ARGS(&cmdList));
-        IM_ASSERT(SUCCEEDED(hr));
 
         // Copy to upload buffer
         void* mapped = nullptr;
@@ -535,8 +532,6 @@ void ImGui_ImplDX12_UpdateTexture(ImTextureData* tex)
         fence->SetEventOnCompletion(1, event);
         ::WaitForSingleObject(event, INFINITE);
 
-        cmdList->Release();
-        cmdAlloc->Release();
         ::CloseHandle(event);
         fence->Release();
         uploadBuffer->Release();
@@ -776,6 +771,14 @@ bool    ImGui_ImplDX12_CreateDeviceObjects()
     if (result_pipeline_state != S_OK)
         return false;
 
+    // Create command allocator and command list for ImGui_ImplDX12_UpdateTexture()
+    HRESULT hr = bd->pd3dDevice->CreateCommandAllocator(D3D12_COMMAND_LIST_TYPE_DIRECT, IID_PPV_ARGS(&bd->pTexCmdAllocator));
+    IM_ASSERT(SUCCEEDED(hr));
+    hr = bd->pd3dDevice->CreateCommandList(0, D3D12_COMMAND_LIST_TYPE_DIRECT, bd->pTexCmdAllocator, nullptr, IID_PPV_ARGS(&bd->pTexCmdList));
+    IM_ASSERT(SUCCEEDED(hr));
+    hr = bd->pTexCmdList->Close();
+    IM_ASSERT(SUCCEEDED(hr));
+
     return true;
 }
 
@@ -790,6 +793,8 @@ void    ImGui_ImplDX12_InvalidateDeviceObjects()
     bd->commandQueueOwned = false;
     SafeRelease(bd->pRootSignature);
     SafeRelease(bd->pPipelineState);
+    SafeRelease(bd->pTexCmdList);
+    SafeRelease(bd->pTexCmdAllocator);
 
     // Destroy all textures
     for (ImTextureData* tex : ImGui::GetPlatformIO().Textures)

docs/CHANGELOG.txt

@@ -73,6 +73,8 @@ Other Changes:
 - Backends: all backends call ImGuiPlatformIO::ClearPlatformHandlers() and
   ClearRendererHandlers() on shutdown, so as not to leave function pointers
   which may be dangling when using backend in e.g. DLL. (#8945, #2769)
+- Backends: DirectX12: reuse a command list and allocator for texture uploads instead
+  of recreating them each time. (#8963, #8465) [@RT2Code]
 - Backends: OpenGL3: fixed GL loader to work on Haiku OS which does not support
   `RTLD_NOLOAD`. (#8952) [@Xottab-DUTY, @threedeyes]
 - Backends: SDL2,SDL3: avoid using the SDL_GetGlobalMouseState() path when one of our