Backends: DirectX12: enable swapchain tearing if available. (#8965)

backends/imgui_impl_dx12.cpp

@@ -21,7 +21,8 @@
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
 //  2025-09-29: DirectX12: Rework synchronization logic. (#8961)
-//  2025-09-29: DirectX12: Reuse a command list and allocator for texture uploads instead of recreating them each time.
+//  2025-09-29: DirectX12: Enable swapchain tearing to eliminate viewports framerate throttling. (#8965)
+//  2025-09-29: DirectX12: Reuse a command list and allocator for texture uploads instead of recreating them each time. (#8963)
 //  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.
@@ -59,7 +60,7 @@
 
 // DirectX
 #include <d3d12.h>
-#include <dxgi1_4.h>
+#include <dxgi1_5.h>
 #include <d3dcompiler.h>
 #ifdef _MSC_VER
 #pragma comment(lib, "d3dcompiler") // Automatically link with d3dcompiler.lib as we are using D3DCompile() below.
@@ -89,6 +90,7 @@ struct ImGui_ImplDX12_Texture
 struct ImGui_ImplDX12_Data
 {
     ImGui_ImplDX12_InitInfo     InitInfo;
+    IDXGIFactory5*              pdxgiFactory;
     ID3D12Device*               pd3dDevice;
     ID3D12RootSignature*        pRootSignature;
     ID3D12PipelineState*        pPipelineState;
@@ -101,6 +103,8 @@ struct ImGui_ImplDX12_Data
     UINT64                      FenceLastSignaledValue;
     HANDLE                      FenceEvent;
     UINT                        numFramesInFlight;
+    bool                        tearingSupport;
+    bool                        LegacySingleDescriptorUsed;
 
     ID3D12CommandAllocator*     pTexCmdAllocator;
     ID3D12GraphicsCommandList*  pTexCmdList;
@@ -108,8 +112,6 @@ struct ImGui_ImplDX12_Data
     ImGui_ImplDX12_RenderBuffers* pFrameResources;
     UINT                        frameIndex;
 
-    bool                        LegacySingleDescriptorUsed;
-
     ImGui_ImplDX12_Data()       { memset((void*)this, 0, sizeof(*this)); }
 };
 
@@ -545,6 +547,13 @@ bool    ImGui_ImplDX12_CreateDeviceObjects()
     if (bd->pPipelineState)
         ImGui_ImplDX12_InvalidateDeviceObjects();
 
+    HRESULT hr = ::CreateDXGIFactory1(IID_PPV_ARGS(&bd->pdxgiFactory));
+    IM_ASSERT(hr == S_OK);
+
+    BOOL allow_tearing = FALSE;
+    bd->pdxgiFactory->CheckFeatureSupport(DXGI_FEATURE_PRESENT_ALLOW_TEARING, &allow_tearing, sizeof(allow_tearing));
+    bd->tearingSupport = (allow_tearing == TRUE);
+
     // Create the root signature
     {
         D3D12_DESCRIPTOR_RANGE descRange = {};
@@ -767,7 +776,7 @@ bool    ImGui_ImplDX12_CreateDeviceObjects()
         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));
+    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));
@@ -789,6 +798,7 @@ void    ImGui_ImplDX12_InvalidateDeviceObjects()
     if (!bd || !bd->pd3dDevice)
         return;
 
+    SafeRelease(bd->pdxgiFactory);
     if (bd->commandQueueOwned)
         SafeRelease(bd->pCommandQueue);
     bd->commandQueueOwned = false;
@@ -853,6 +863,7 @@ bool ImGui_ImplDX12_Init(ImGui_ImplDX12_InitInfo* init_info)
     bd->DSVFormat = init_info->DSVFormat;
     bd->numFramesInFlight = init_info->NumFramesInFlight;
     bd->pd3dSrvDescHeap = init_info->SrvDescriptorHeap;
+    bd->tearingSupport = false;
 
     io.BackendRendererUserData = (void*)bd;
     io.BackendRendererName = "imgui_impl_dx12";

docs/CHANGELOG.txt

@@ -77,6 +77,7 @@ Other Changes:
   of recreating them each time. (#8963, #8465) [@RT2Code]
 - Backends: DirectX12: Rework synchronization logic. (#8961) [@RT2Code]
   (presumably fixes old hard-to-repro crash issues such as #3463, #5018)
+- Backends: DirectX12: Enable swapchain tearing if available. (#8965) [@RT2Code]
 - Backends: OpenGL3: fixed GL loader to work on Haiku OS which does not support
   `RTLD_NOLOAD`. (#8952) [@Xottab-DUTY, @threedeyes]
 - Backends: GLFW: fixed build on platform that are neither Windows, macOS or

examples/example_win32_directx12/main.cpp

@@ -10,7 +10,7 @@
 #include "imgui_impl_win32.h"
 #include "imgui_impl_dx12.h"
 #include <d3d12.h>
-#include <dxgi1_4.h>
+#include <dxgi1_5.h>
 #include <tchar.h>
 
 #ifdef _DEBUG
@@ -92,6 +92,7 @@ static ID3D12Fence*                 g_fence = nullptr;
 static HANDLE                       g_fenceEvent = nullptr;
 static UINT64                       g_fenceLastSignaledValue = 0;
 static IDXGISwapChain3*             g_pSwapChain = nullptr;
+static bool                         g_SwapChainTearingSupport = false;
 static bool                         g_SwapChainOccluded = false;
 static HANDLE                       g_hSwapChainWaitableObject = nullptr;
 static ID3D12Resource*              g_mainRenderTargetResource[APP_NUM_BACK_BUFFERS] = {};
@@ -287,7 +288,7 @@ int main(int, char**)
 
         // Present
         HRESULT hr = g_pSwapChain->Present(1, 0);   // Present with vsync
-        //HRESULT hr = g_pSwapChain->Present(0, 0); // Present without vsync
+        //HRESULT hr = g_pSwapChain->Present(0, g_SwapChainTearingSupport ? DXGI_PRESENT_ALLOW_TEARING : 0); // Present without vsync
         g_SwapChainOccluded = (hr == DXGI_STATUS_OCCLUDED);
         g_frameIndex++;
     }
@@ -407,14 +408,24 @@ bool CreateDeviceD3D(HWND hWnd)
         return false;
 
     {
-        IDXGIFactory4* dxgiFactory = nullptr;
+        IDXGIFactory5* dxgiFactory = nullptr;
         IDXGISwapChain1* swapChain1 = nullptr;
         if (CreateDXGIFactory1(IID_PPV_ARGS(&dxgiFactory)) != S_OK)
             return false;
+
+        BOOL allow_tearing = FALSE;
+        dxgiFactory->CheckFeatureSupport(DXGI_FEATURE_PRESENT_ALLOW_TEARING, &allow_tearing, sizeof(allow_tearing));
+        g_SwapChainTearingSupport = (allow_tearing == TRUE);
+        if (g_SwapChainTearingSupport)
+            sd.Flags |= DXGI_SWAP_CHAIN_FLAG_ALLOW_TEARING;
+
         if (dxgiFactory->CreateSwapChainForHwnd(g_pd3dCommandQueue, hWnd, &sd, nullptr, nullptr, &swapChain1) != S_OK)
             return false;
         if (swapChain1->QueryInterface(IID_PPV_ARGS(&g_pSwapChain)) != S_OK)
             return false;
+        if (g_SwapChainTearingSupport)
+            dxgiFactory->MakeWindowAssociation(hWnd, DXGI_MWA_NO_ALT_ENTER);
+
         swapChain1->Release();
         dxgiFactory->Release();
         g_pSwapChain->SetMaximumFrameLatency(APP_NUM_BACK_BUFFERS);
@@ -511,7 +522,9 @@ LRESULT WINAPI WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
         if (g_pd3dDevice != nullptr && wParam != SIZE_MINIMIZED)
         {
             CleanupRenderTarget();
-            HRESULT result = g_pSwapChain->ResizeBuffers(0, (UINT)LOWORD(lParam), (UINT)HIWORD(lParam), DXGI_FORMAT_UNKNOWN, DXGI_SWAP_CHAIN_FLAG_FRAME_LATENCY_WAITABLE_OBJECT);
+            DXGI_SWAP_CHAIN_DESC1 desc = {};
+            g_pSwapChain->GetDesc1(&desc);
+            HRESULT result = g_pSwapChain->ResizeBuffers(0, (UINT)LOWORD(lParam), (UINT)HIWORD(lParam), desc.Format, desc.Flags);
             assert(SUCCEEDED(result) && "Failed to resize swapchain.");
             CreateRenderTarget();
         }