From bd9a37bc600a4281d74ef429fb23ee8e002b217d Mon Sep 17 00:00:00 2001
From: ocornut <omar@miracleworld.net>
Date: Mon, 29 Sep 2025 16:27:12 +0200
Subject: [PATCH] Backends: DX12: Use one fence instead of one by viewport.
 (docking) (#8961)

---
 backends/imgui_impl_dx12.cpp | 36 ++++++++++--------------------------
 1 file changed, 10 insertions(+), 26 deletions(-)

diff --git a/backends/imgui_impl_dx12.cpp b/backends/imgui_impl_dx12.cpp
index 9fbdc4426..68e379b03 100644
--- a/backends/imgui_impl_dx12.cpp
+++ b/backends/imgui_impl_dx12.cpp
@@ -152,9 +152,6 @@ struct ImGui_ImplDX12_ViewportData
     ID3D12DescriptorHeap*           RtvDescHeap;
     IDXGISwapChain3*                SwapChain;
     HANDLE                          SwapChainWaitableObject;
-    ID3D12Fence*                    Fence;
-    UINT64                          FenceLastSignaledValue;
-    HANDLE                          FenceEvent;
     UINT                            NumFramesInFlight;
     ImGui_ImplDX12_FrameContext*    FrameCtx;
 
@@ -169,9 +166,6 @@ struct ImGui_ImplDX12_ViewportData
         RtvDescHeap = nullptr;
         SwapChain = nullptr;
         SwapChainWaitableObject = nullptr;
-        Fence = nullptr;
-        FenceLastSignaledValue = 0;
-        FenceEvent = nullptr;
         NumFramesInFlight = num_frames_in_flight;
         FrameCtx = new ImGui_ImplDX12_FrameContext[NumFramesInFlight];
         FrameIndex = 0;
@@ -196,8 +190,6 @@ struct ImGui_ImplDX12_ViewportData
         IM_ASSERT(RtvDescHeap == nullptr);
         IM_ASSERT(SwapChain == nullptr);
         IM_ASSERT(SwapChainWaitableObject == nullptr);
-        IM_ASSERT(Fence == nullptr);
-        IM_ASSERT(FenceEvent == nullptr);
 
         for (UINT i = 0; i < NumFramesInFlight; ++i)
         {
@@ -1065,13 +1057,6 @@ static void ImGui_ImplDX12_CreateWindow(ImGuiViewport* viewport)
     IM_ASSERT(res == S_OK);
     vd->CommandList->Close();
 
-    // Create fence.
-    res = bd->pd3dDevice->CreateFence(0, D3D12_FENCE_FLAG_NONE, IID_PPV_ARGS(&vd->Fence));
-    IM_ASSERT(res == S_OK);
-
-    vd->FenceEvent = CreateEvent(nullptr, FALSE, FALSE, nullptr);
-    IM_ASSERT(vd->FenceEvent != nullptr);
-
     // Create swap chain
     // FIXME-VIEWPORT: May want to copy/inherit swap chain settings from the user/application.
     DXGI_SWAP_CHAIN_DESC1 sd1;
@@ -1146,22 +1131,24 @@ static void ImGui_ImplDX12_CreateWindow(ImGuiViewport* viewport)
 
 static void ImGui_WaitForPendingOperations(ImGui_ImplDX12_ViewportData* vd)
 {
-    HRESULT hr = vd->CommandQueue->Signal(vd->Fence, ++vd->FenceLastSignaledValue);
+    ImGui_ImplDX12_Data* bd = ImGui_ImplDX12_GetBackendData();
+    HRESULT hr = vd->CommandQueue->Signal(bd->Fence, ++bd->FenceLastSignaledValue);
     IM_ASSERT(hr == S_OK);
 
-    hr = vd->Fence->SetEventOnCompletion(vd->FenceLastSignaledValue, vd->FenceEvent);
+    hr = bd->Fence->SetEventOnCompletion(bd->FenceLastSignaledValue, bd->FenceEvent);
     IM_ASSERT(hr == S_OK);
-    ::WaitForSingleObject(vd->FenceEvent, INFINITE);
+    ::WaitForSingleObject(bd->FenceEvent, INFINITE);
 }
 
 static ImGui_ImplDX12_FrameContext* ImGui_WaitForNextFrameContext(ImGui_ImplDX12_ViewportData* vd)
 {
+    ImGui_ImplDX12_Data* bd = ImGui_ImplDX12_GetBackendData();
     ImGui_ImplDX12_FrameContext* frame_context = &vd->FrameCtx[vd->FrameIndex % vd->NumFramesInFlight];
-    if (vd->Fence->GetCompletedValue() < frame_context->FenceValue)
+    if (bd->Fence->GetCompletedValue() < frame_context->FenceValue)
     {
-        HRESULT hr = vd->Fence->SetEventOnCompletion(frame_context->FenceValue, vd->FenceEvent);
+        HRESULT hr = bd->Fence->SetEventOnCompletion(frame_context->FenceValue, bd->FenceEvent);
         IM_ASSERT(hr == S_OK);
-        HANDLE waitableObjects[] = { vd->SwapChainWaitableObject, vd->FenceEvent };
+        HANDLE waitableObjects[] = { vd->SwapChainWaitableObject, bd->FenceEvent };
         ::WaitForMultipleObjects(2, waitableObjects, TRUE, INFINITE);
     }
     else
@@ -1185,9 +1172,6 @@ static void ImGui_ImplDX12_DestroyWindow(ImGuiViewport* viewport)
         SafeRelease(vd->CommandList);
         SafeRelease(vd->SwapChain);
         SafeRelease(vd->RtvDescHeap);
-        SafeRelease(vd->Fence);
-        ::CloseHandle(vd->FenceEvent);
-        vd->FenceEvent = nullptr;
 
         for (UINT i = 0; i < bd->numFramesInFlight; i++)
         {
@@ -1260,9 +1244,9 @@ static void ImGui_ImplDX12_RenderWindow(ImGuiViewport* viewport, void*)
 
     vd->CommandQueue->ExecuteCommandLists(1, (ID3D12CommandList* const*)&cmd_list);
 
-    HRESULT hr = vd->CommandQueue->Signal(vd->Fence, ++vd->FenceLastSignaledValue);
+    HRESULT hr = vd->CommandQueue->Signal(bd->Fence, ++bd->FenceLastSignaledValue);
     IM_ASSERT(hr == S_OK);
-    frame_context->FenceValue = vd->FenceLastSignaledValue;
+    frame_context->FenceValue = bd->FenceLastSignaledValue;
 }
 
 static void ImGui_ImplDX12_SwapBuffers(ImGuiViewport* viewport, void*)