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Backends: DX12: Let user specifies the backbuffer count by setting ImGui_ImplDX12_InitInfo::BackBuffer and add support for a single frame in flight. #9035

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Backends: DX12: Let user specifies the backbuffer count by setting ImGui_ImplDX12_InitInfo::BackBuffer and add support for a single frame in flight. #9035

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6f07596
Let user specifies the back buffer count by setting ImGui_ImplDX12_In…
RT2Code Oct 25, 2025
b4cfad5
Match SetMaximumFrameLatency to the number of frames in flight
RT2Code Nov 10, 2025
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72 changes: 44 additions & 28 deletions backends/imgui_impl_dx12.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@
// CHANGELOG
// (minor and older changes stripped away, please see git history for details)
// 2025-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
// 2025-10-25: [Docking] DirectX12: Let user specifies viewports backbuffer count by setting ImGui_ImplDX12_InitInfo::BackBuffer and add support for a single frame in flight.
// 2025-10-23: [Docking] DirectX12: Fixed an issue in synchronization logic improving rendering throughput for secondary viewports. (#8961, #9025)
// 2025-10-11: DirectX12: Reuse texture upload buffer and grow it only when necessary. (#9002)
// 2025-09-29: DirectX12: Rework synchronization logic. (#8961)
Expand Down Expand Up @@ -107,6 +108,7 @@ struct ImGui_ImplDX12_Data
ID3D12Fence* Fence;
UINT64 FenceLastSignaledValue;
HANDLE FenceEvent;
UINT numBackbuffer;
UINT numFramesInFlight;
bool tearingSupport;
bool LegacySingleDescriptorUsed;
Expand Down Expand Up @@ -136,13 +138,18 @@ struct ImGui_ImplDX12_RenderBuffers
int VertexBufferSize;
};

// Backbuffers used for secondary viewports created by the multi-viewports systems
struct ImGui_ImplDX12_Backbuffer
{
ID3D12Resource* RenderTarget;
D3D12_CPU_DESCRIPTOR_HANDLE RenderTargetCpuDescriptors;
};

// Buffers used for secondary viewports created by the multi-viewports systems
struct ImGui_ImplDX12_FrameContext
{
UINT64 FenceValue;
ID3D12CommandAllocator* CommandAllocator;
ID3D12Resource* RenderTarget;
D3D12_CPU_DESCRIPTOR_HANDLE RenderTargetCpuDescriptors;
};

// Helper structure we store in the void* RendererUserData field of each ImGuiViewport to easily retrieve our backend data.
Expand All @@ -156,30 +163,35 @@ struct ImGui_ImplDX12_ViewportData
ID3D12DescriptorHeap* RtvDescHeap;
IDXGISwapChain3* SwapChain;
HANDLE SwapChainWaitableObject;
UINT NumBackBuffer;
ImGui_ImplDX12_Backbuffer* BackBuffer;
UINT NumFramesInFlight;
ImGui_ImplDX12_FrameContext* FrameCtx;

// Render buffers
UINT FrameIndex;
ImGui_ImplDX12_RenderBuffers* FrameRenderBuffers;

ImGui_ImplDX12_ViewportData(UINT num_frames_in_flight)
ImGui_ImplDX12_ViewportData(UINT num_backbuffer, UINT num_frames_in_flight)
{
CommandQueue = nullptr;
CommandList = nullptr;
RtvDescHeap = nullptr;
SwapChain = nullptr;
SwapChainWaitableObject = nullptr;
NumBackBuffer = num_backbuffer;
BackBuffer = new ImGui_ImplDX12_Backbuffer[num_backbuffer];
NumFramesInFlight = num_frames_in_flight;
FrameCtx = new ImGui_ImplDX12_FrameContext[NumFramesInFlight];
FrameIndex = 0;
FrameRenderBuffers = new ImGui_ImplDX12_RenderBuffers[NumFramesInFlight];

for (UINT i = 0; i < NumBackBuffer; ++i)
BackBuffer[i].RenderTarget = nullptr;

for (UINT i = 0; i < NumFramesInFlight; ++i)
{
FrameCtx[i].FenceValue = 0;
FrameCtx[i].CommandAllocator = nullptr;
FrameCtx[i].RenderTarget = nullptr;

// Create buffers with a default size (they will later be grown as needed)
FrameRenderBuffers[i].IndexBuffer = nullptr;
Expand All @@ -195,12 +207,16 @@ struct ImGui_ImplDX12_ViewportData
IM_ASSERT(SwapChain == nullptr);
IM_ASSERT(SwapChainWaitableObject == nullptr);

for (UINT i = 0; i < NumBackBuffer; ++i)
IM_ASSERT(BackBuffer[i].RenderTarget == nullptr);

for (UINT i = 0; i < NumFramesInFlight; ++i)
{
IM_ASSERT(FrameCtx[i].CommandAllocator == nullptr && FrameCtx[i].RenderTarget == nullptr);
IM_ASSERT(FrameCtx[i].CommandAllocator == nullptr);
IM_ASSERT(FrameRenderBuffers[i].IndexBuffer == nullptr && FrameRenderBuffers[i].VertexBuffer == nullptr);
}

delete[] BackBuffer; BackBuffer = nullptr;
delete[] FrameCtx; FrameCtx = nullptr;
delete[] FrameRenderBuffers; FrameRenderBuffers = nullptr;
}
Expand Down Expand Up @@ -955,6 +971,7 @@ bool ImGui_ImplDX12_Init(ImGui_ImplDX12_InitInfo* init_info)
bd->pCommandQueue = init_info->CommandQueue;
bd->RTVFormat = init_info->RTVFormat;
bd->DSVFormat = init_info->DSVFormat;
bd->numBackbuffer = init_info->NumBackBuffer >= 2 ? init_info->NumBackBuffer : 2;
bd->numFramesInFlight = init_info->NumFramesInFlight;
bd->pd3dSrvDescHeap = init_info->SrvDescriptorHeap;
bd->tearingSupport = false;
Expand All @@ -971,7 +988,7 @@ bool ImGui_ImplDX12_Init(ImGui_ImplDX12_InitInfo* init_info)
// Create a dummy ImGui_ImplDX12_ViewportData holder for the main viewport,
// Since this is created and managed by the application, we will only use the ->Resources[] fields.
ImGuiViewport* main_viewport = ImGui::GetMainViewport();
main_viewport->RendererUserData = IM_NEW(ImGui_ImplDX12_ViewportData)(bd->numFramesInFlight);
main_viewport->RendererUserData = IM_NEW(ImGui_ImplDX12_ViewportData)(0, bd->numFramesInFlight);

#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
if (init_info->SrvDescriptorAllocFn == nullptr)
Expand Down Expand Up @@ -1059,7 +1076,7 @@ void ImGui_ImplDX12_NewFrame()
static void ImGui_ImplDX12_CreateWindow(ImGuiViewport* viewport)
{
ImGui_ImplDX12_Data* bd = ImGui_ImplDX12_GetBackendData();
ImGui_ImplDX12_ViewportData* vd = IM_NEW(ImGui_ImplDX12_ViewportData)(bd->numFramesInFlight);
ImGui_ImplDX12_ViewportData* vd = IM_NEW(ImGui_ImplDX12_ViewportData)(bd->numBackbuffer, bd->numFramesInFlight);
viewport->RendererUserData = vd;

// PlatformHandleRaw should always be a HWND, whereas PlatformHandle might be a higher-level handle (e.g. GLFWWindow*, SDL's WindowID).
Expand Down Expand Up @@ -1088,7 +1105,7 @@ static void ImGui_ImplDX12_CreateWindow(ImGuiViewport* viewport)
// FIXME-VIEWPORT: May want to copy/inherit swap chain settings from the user/application.
DXGI_SWAP_CHAIN_DESC1 sd1;
ZeroMemory(&sd1, sizeof(sd1));
sd1.BufferCount = bd->numFramesInFlight;
sd1.BufferCount = bd->numBackbuffer;
sd1.Width = (UINT)viewport->Size.x;
sd1.Height = (UINT)viewport->Size.y;
sd1.Format = bd->RTVFormat;
Expand Down Expand Up @@ -1120,7 +1137,7 @@ static void ImGui_ImplDX12_CreateWindow(ImGuiViewport* viewport)
{
D3D12_DESCRIPTOR_HEAP_DESC desc = {};
desc.Type = D3D12_DESCRIPTOR_HEAP_TYPE_RTV;
desc.NumDescriptors = bd->numFramesInFlight;
desc.NumDescriptors = bd->numBackbuffer;
desc.Flags = D3D12_DESCRIPTOR_HEAP_FLAG_NONE;
desc.NodeMask = 1;

Expand All @@ -1129,19 +1146,16 @@ static void ImGui_ImplDX12_CreateWindow(ImGuiViewport* viewport)

SIZE_T rtv_descriptor_size = bd->pd3dDevice->GetDescriptorHandleIncrementSize(D3D12_DESCRIPTOR_HEAP_TYPE_RTV);
D3D12_CPU_DESCRIPTOR_HANDLE rtv_handle = vd->RtvDescHeap->GetCPUDescriptorHandleForHeapStart();
for (UINT i = 0; i < bd->numFramesInFlight; i++)
ID3D12Resource* back_buffer;
for (UINT i = 0; i < bd->numBackbuffer; i++)
{
vd->FrameCtx[i].RenderTargetCpuDescriptors = rtv_handle;
vd->BackBuffer[i].RenderTargetCpuDescriptors = rtv_handle;
rtv_handle.ptr += rtv_descriptor_size;
}

ID3D12Resource* back_buffer;
for (UINT i = 0; i < bd->numFramesInFlight; i++)
{
IM_ASSERT(vd->FrameCtx[i].RenderTarget == nullptr);
IM_ASSERT(vd->BackBuffer[i].RenderTarget == nullptr);
vd->SwapChain->GetBuffer(i, IID_PPV_ARGS(&back_buffer));
bd->pd3dDevice->CreateRenderTargetView(back_buffer, nullptr, vd->FrameCtx[i].RenderTargetCpuDescriptors);
vd->FrameCtx[i].RenderTarget = back_buffer;
bd->pd3dDevice->CreateRenderTargetView(back_buffer, nullptr, vd->BackBuffer[i].RenderTargetCpuDescriptors);
vd->BackBuffer[i].RenderTarget = back_buffer;
}

hr = vd->SwapChain->SetMaximumFrameLatency(bd->numFramesInFlight);
Expand Down Expand Up @@ -1197,9 +1211,11 @@ static void ImGui_ImplDX12_DestroyWindow(ImGuiViewport* viewport)
SafeRelease(vd->SwapChain);
SafeRelease(vd->RtvDescHeap);

for (UINT i = 0; i < bd->numBackbuffer; i++)
SafeRelease(vd->BackBuffer[i].RenderTarget);

for (UINT i = 0; i < bd->numFramesInFlight; i++)
{
SafeRelease(vd->FrameCtx[i].RenderTarget);
SafeRelease(vd->FrameCtx[i].CommandAllocator);
ImGui_ImplDX12_DestroyRenderBuffers(&vd->FrameRenderBuffers[i]);
}
Expand All @@ -1215,20 +1231,20 @@ static void ImGui_ImplDX12_SetWindowSize(ImGuiViewport* viewport, ImVec2 size)

ImGui_WaitForPendingOperations(vd);

for (UINT i = 0; i < bd->numFramesInFlight; i++)
SafeRelease(vd->FrameCtx[i].RenderTarget);
for (UINT i = 0; i < bd->numBackbuffer; i++)
SafeRelease(vd->BackBuffer[i].RenderTarget);

if (vd->SwapChain)
{
ID3D12Resource* back_buffer = nullptr;
DXGI_SWAP_CHAIN_DESC1 desc = {};
vd->SwapChain->GetDesc1(&desc);
vd->SwapChain->ResizeBuffers(0, (UINT)size.x, (UINT)size.y, desc.Format, desc.Flags);
for (UINT i = 0; i < bd->numFramesInFlight; i++)
for (UINT i = 0; i < bd->numBackbuffer; i++)
{
vd->SwapChain->GetBuffer(i, IID_PPV_ARGS(&back_buffer));
bd->pd3dDevice->CreateRenderTargetView(back_buffer, nullptr, vd->FrameCtx[i].RenderTargetCpuDescriptors);
vd->FrameCtx[i].RenderTarget = back_buffer;
bd->pd3dDevice->CreateRenderTargetView(back_buffer, nullptr, vd->BackBuffer[i].RenderTargetCpuDescriptors);
vd->BackBuffer[i].RenderTarget = back_buffer;
}
}
}
Expand All @@ -1245,7 +1261,7 @@ static void ImGui_ImplDX12_RenderWindow(ImGuiViewport* viewport, void*)
D3D12_RESOURCE_BARRIER barrier = {};
barrier.Type = D3D12_RESOURCE_BARRIER_TYPE_TRANSITION;
barrier.Flags = D3D12_RESOURCE_BARRIER_FLAG_NONE;
barrier.Transition.pResource = vd->FrameCtx[back_buffer_idx].RenderTarget;
barrier.Transition.pResource = vd->BackBuffer[back_buffer_idx].RenderTarget;
barrier.Transition.Subresource = D3D12_RESOURCE_BARRIER_ALL_SUBRESOURCES;
barrier.Transition.StateBefore = D3D12_RESOURCE_STATE_PRESENT;
barrier.Transition.StateAfter = D3D12_RESOURCE_STATE_RENDER_TARGET;
Expand All @@ -1256,9 +1272,9 @@ static void ImGui_ImplDX12_RenderWindow(ImGuiViewport* viewport, void*)
frame_context->CommandAllocator->Reset();
cmd_list->Reset(frame_context->CommandAllocator, nullptr);
cmd_list->ResourceBarrier(1, &barrier);
cmd_list->OMSetRenderTargets(1, &vd->FrameCtx[back_buffer_idx].RenderTargetCpuDescriptors, FALSE, nullptr);
cmd_list->OMSetRenderTargets(1, &vd->BackBuffer[back_buffer_idx].RenderTargetCpuDescriptors, FALSE, nullptr);
if (!(viewport->Flags & ImGuiViewportFlags_NoRendererClear))
cmd_list->ClearRenderTargetView(vd->FrameCtx[back_buffer_idx].RenderTargetCpuDescriptors, (const float*)&clear_color, 0, nullptr);
cmd_list->ClearRenderTargetView(vd->BackBuffer[back_buffer_idx].RenderTargetCpuDescriptors, (const float*)&clear_color, 0, nullptr);
cmd_list->SetDescriptorHeaps(1, &bd->pd3dSrvDescHeap);

ImGui_ImplDX12_RenderDrawData(viewport->DrawData, cmd_list);
Expand Down
1 change: 1 addition & 0 deletions backends/imgui_impl_dx12.h
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@ struct ImGui_ImplDX12_InitInfo
{
ID3D12Device* Device;
ID3D12CommandQueue* CommandQueue; // Command queue used for queuing texture uploads.
int NumBackBuffer;
int NumFramesInFlight;
DXGI_FORMAT RTVFormat; // RenderTarget format.
DXGI_FORMAT DSVFormat; // DepthStencilView format.
Expand Down
3 changes: 2 additions & 1 deletion examples/example_win32_directx12/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -166,6 +166,7 @@ int main(int, char**)
ImGui_ImplDX12_InitInfo init_info = {};
init_info.Device = g_pd3dDevice;
init_info.CommandQueue = g_pd3dCommandQueue;
init_info.NumBackBuffer = APP_NUM_BACK_BUFFERS;
init_info.NumFramesInFlight = APP_NUM_FRAMES_IN_FLIGHT;
init_info.RTVFormat = DXGI_FORMAT_R8G8B8A8_UNORM;
init_info.DSVFormat = DXGI_FORMAT_UNKNOWN;
Expand Down Expand Up @@ -449,7 +450,7 @@ bool CreateDeviceD3D(HWND hWnd)

swapChain1->Release();
dxgiFactory->Release();
g_pSwapChain->SetMaximumFrameLatency(APP_NUM_BACK_BUFFERS);
g_pSwapChain->SetMaximumFrameLatency(APP_NUM_FRAMES_IN_FLIGHT);
g_hSwapChainWaitableObject = g_pSwapChain->GetFrameLatencyWaitableObject();
}

Expand Down