(Breaking) Backends: DX12: changed ImGui_ImplDX12_Init() signature. Added ImGui_ImplDX12_InitInfo. Added support for Srv allocators.

Ref 7708

Author: ocornut

backends/imgui_impl_dx12.cpp

@@ -19,6 +19,8 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2024-11-15: DirectX12: *BREAKING CHANGE* Changed ImGui_ImplDX12_Init() signature to take a ImGui_ImplDX12_InitInfo struct. Legacy ImGui_ImplDX12_Init() signature is still supported (will obsolete).
+//  2024-11-15: DirectX12: *BREAKING CHANGE* User is now required to pass function pointers to allocate/free SRV Descriptors. We provide convenience legacy fields to pass a single descriptor, matching the old API, but upcoming features will want multiple.
 //  2024-10-23: DirectX12: Unmap() call specify written range. The range is informational and may be used by debug tools.
 //  2024-10-07: DirectX12: Changed default texture sampler to Clamp instead of Repeat/Wrap.
 //  2024-10-07: DirectX12: Expose selected render state in ImGui_ImplDX12_RenderState, which you can access in 'void* platform_io.Renderer_RenderState' during draw callbacks.
@@ -57,6 +59,7 @@
 struct ImGui_ImplDX12_RenderBuffers;
 struct ImGui_ImplDX12_Data
 {
+    ImGui_ImplDX12_InitInfo     InitInfo;
     ID3D12Device*               pd3dDevice;
     ID3D12RootSignature*        pRootSignature;
     ID3D12PipelineState*        pPipelineState;
@@ -695,8 +698,14 @@ void    ImGui_ImplDX12_InvalidateDeviceObjects()
     ImGuiIO& io = ImGui::GetIO();
     SafeRelease(bd->pRootSignature);
     SafeRelease(bd->pPipelineState);
+
+    // Free SRV descriptor used by texture
+#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+    if (bd->InitInfo.SrvDescriptorFreeFn != NULL)
+#endif
+        bd->InitInfo.SrvDescriptorFreeFn(&bd->InitInfo, bd->hFontSrvCpuDescHandle, bd->hFontSrvGpuDescHandle);
     SafeRelease(bd->pFontTextureResource);
-    io.Fonts->SetTexID(0); // We copied bd->pFontTextureView to io.Fonts->TexID so let's clear that as well.
+    io.Fonts->SetTexID(0); // We copied bd->hFontSrvGpuDescHandle to io.Fonts->TexID so let's clear that as well.
 
     for (UINT i = 0; i < bd->numFramesInFlight; i++)
     {
@@ -706,30 +715,47 @@ void    ImGui_ImplDX12_InvalidateDeviceObjects()
     }
 }
 
-bool ImGui_ImplDX12_Init(ID3D12Device* device, int num_frames_in_flight, DXGI_FORMAT rtv_format, ID3D12DescriptorHeap* cbv_srv_heap,
-                         D3D12_CPU_DESCRIPTOR_HANDLE font_srv_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE font_srv_gpu_desc_handle)
+bool ImGui_ImplDX12_Init(ImGui_ImplDX12_InitInfo* init_info)
 {
     ImGuiIO& io = ImGui::GetIO();
     IMGUI_CHECKVERSION();
     IM_ASSERT(io.BackendRendererUserData == nullptr && "Already initialized a renderer backend!");
 
     // Setup backend capabilities flags
     ImGui_ImplDX12_Data* bd = IM_NEW(ImGui_ImplDX12_Data)();
+
+    bd->InitInfo = *init_info; // Deep copy
+    bd->pd3dDevice = init_info->Device;
+    bd->RTVFormat = init_info->RTVFormat;
+    bd->numFramesInFlight = init_info->NumFramesInFlight;
+    bd->pd3dSrvDescHeap = init_info->SrvDescriptorHeap;
+
     io.BackendRendererUserData = (void*)bd;
     io.BackendRendererName = "imgui_impl_dx12";
     io.BackendFlags |= ImGuiBackendFlags_RendererHasVtxOffset;  // We can honor the ImDrawCmd::VtxOffset field, allowing for large meshes.
 
-    bd->pd3dDevice = device;
-    bd->RTVFormat = rtv_format;
-    bd->hFontSrvCpuDescHandle = font_srv_cpu_desc_handle;
-    bd->hFontSrvGpuDescHandle = font_srv_gpu_desc_handle;
-    bd->pFrameResources = new ImGui_ImplDX12_RenderBuffers[num_frames_in_flight];
-    bd->numFramesInFlight = num_frames_in_flight;
-    bd->pd3dSrvDescHeap = cbv_srv_heap;
-    bd->frameIndex = UINT_MAX;
+    // Allocate 1 SRV descriptor for the font texture
+    if (init_info->SrvDescriptorAllocFn != NULL)
+    {
+        IM_ASSERT(init_info->SrvDescriptorFreeFn != NULL);
+        init_info->SrvDescriptorAllocFn(&bd->InitInfo, &bd->hFontSrvCpuDescHandle, &bd->hFontSrvGpuDescHandle);
+    }
+    else
+    {
+#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+        IM_ASSERT(init_info->LegacySingleSrvCpuDescriptor.ptr != 0 && init_info->LegacySingleSrvGpuDescriptor.ptr != 0);
+        bd->hFontSrvCpuDescHandle = init_info->LegacySingleSrvCpuDescriptor;
+        bd->hFontSrvGpuDescHandle = init_info->LegacySingleSrvGpuDescriptor;
+#else
+        IM_ASSERT(init_info->SrvDescriptorAllocFn != NULL);
+        IM_ASSERT(init_info->SrvDescriptorFreeFn != NULL);
+#endif
+    }
 
     // Create buffers with a default size (they will later be grown as needed)
-    for (int i = 0; i < num_frames_in_flight; i++)
+    bd->frameIndex = UINT_MAX;
+    bd->pFrameResources = new ImGui_ImplDX12_RenderBuffers[bd->numFramesInFlight];
+    for (int i = 0; i < (int)bd->numFramesInFlight; i++)
     {
         ImGui_ImplDX12_RenderBuffers* fr = &bd->pFrameResources[i];
         fr->IndexBuffer = nullptr;
@@ -741,6 +767,22 @@ bool ImGui_ImplDX12_Init(ID3D12Device* device, int num_frames_in_flight, DXGI_FO
     return true;
 }
 
+#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+// Legacy initialization API Obsoleted in 1.91.5
+// font_srv_cpu_desc_handle and font_srv_gpu_desc_handle are handles to a single SRV descriptor to use for the internal font texture, they must be in 'srv_descriptor_heap'
+bool ImGui_ImplDX12_Init(ID3D12Device* device, int num_frames_in_flight, DXGI_FORMAT rtv_format, ID3D12DescriptorHeap* srv_descriptor_heap, D3D12_CPU_DESCRIPTOR_HANDLE font_srv_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE font_srv_gpu_desc_handle)
+{
+    ImGui_ImplDX12_InitInfo init_info;
+    init_info.Device = device;
+    init_info.NumFramesInFlight = num_frames_in_flight;
+    init_info.RTVFormat = rtv_format;
+    init_info.SrvDescriptorHeap = srv_descriptor_heap;
+    init_info.LegacySingleSrvCpuDescriptor = font_srv_cpu_desc_handle;
+    init_info.LegacySingleSrvGpuDescriptor = font_srv_gpu_desc_handle;;
+    return ImGui_ImplDX12_Init(&init_info);
+}
+#endif
+
 void ImGui_ImplDX12_Shutdown()
 {
     ImGui_ImplDX12_Data* bd = ImGui_ImplDX12_GetBackendData();
@@ -750,6 +792,7 @@ void ImGui_ImplDX12_Shutdown()
     // Clean up windows and device objects
     ImGui_ImplDX12_InvalidateDeviceObjects();
     delete[] bd->pFrameResources;
+
     io.BackendRendererName = nullptr;
     io.BackendRendererUserData = nullptr;
     io.BackendFlags &= ~ImGuiBackendFlags_RendererHasVtxOffset;

backends/imgui_impl_dx12.h

@@ -21,24 +21,42 @@
 #include "imgui.h"      // IMGUI_IMPL_API
 #ifndef IMGUI_DISABLE
 #include <dxgiformat.h> // DXGI_FORMAT
+#include <d3d12.h>      // D3D12_CPU_DESCRIPTOR_HANDLE
 
-struct ID3D12Device;
-struct ID3D12DescriptorHeap;
-struct ID3D12GraphicsCommandList;
-struct D3D12_CPU_DESCRIPTOR_HANDLE;
-struct D3D12_GPU_DESCRIPTOR_HANDLE;
+// Initialization data, for ImGui_ImplDX12_Init()
+struct ImGui_ImplDX12_InitInfo
+{
+    ID3D12Device*               Device;
+    ID3D12CommandQueue*         CommandQueue;
+    int                         NumFramesInFlight;
+    DXGI_FORMAT                 RTVFormat;
+    void*                       UserData;
 
-// Follow "Getting Started" link and check examples/ folder to learn about using backends!
+    // Allocating SRV descriptors for textures is up to the application, so we provide callbacks.
+    // (current version of the backend will only allocate one descriptor, future versions will need to allocate more)
+    ID3D12DescriptorHeap*       SrvDescriptorHeap;
+    void                        (*SrvDescriptorAllocFn)(ImGui_ImplDX12_InitInfo* info, D3D12_CPU_DESCRIPTOR_HANDLE* out_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE* out_gpu_desc_handle);
+    void                        (*SrvDescriptorFreeFn)(ImGui_ImplDX12_InitInfo* info, D3D12_CPU_DESCRIPTOR_HANDLE cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE gpu_desc_handle);
+#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+    D3D12_CPU_DESCRIPTOR_HANDLE LegacySingleSrvCpuDescriptor; // To facilitate transition from single descriptor to allocator callback, you may use those.
+    D3D12_GPU_DESCRIPTOR_HANDLE LegacySingleSrvGpuDescriptor;
+#endif
 
-// Before calling the render function, caller must prepare the command list by resetting it and setting the appropriate
-// render target and descriptor heap that contains font_srv_cpu_desc_handle/font_srv_gpu_desc_handle.
-// font_srv_cpu_desc_handle and font_srv_gpu_desc_handle are handles to a single SRV descriptor to use for the internal font texture.
-IMGUI_IMPL_API bool     ImGui_ImplDX12_Init(ID3D12Device* device, int num_frames_in_flight, DXGI_FORMAT rtv_format, ID3D12DescriptorHeap* cbv_srv_heap,
-                                            D3D12_CPU_DESCRIPTOR_HANDLE font_srv_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE font_srv_gpu_desc_handle);
+    ImGui_ImplDX12_InitInfo()   { memset(this, 0, sizeof(*this)); }
+};
+
+// Follow "Getting Started" link and check examples/ folder to learn about using backends!
+IMGUI_IMPL_API bool     ImGui_ImplDX12_Init(ImGui_ImplDX12_InitInfo* info);
 IMGUI_IMPL_API void     ImGui_ImplDX12_Shutdown();
 IMGUI_IMPL_API void     ImGui_ImplDX12_NewFrame();
 IMGUI_IMPL_API void     ImGui_ImplDX12_RenderDrawData(ImDrawData* draw_data, ID3D12GraphicsCommandList* graphics_command_list);
 
+#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+// Legacy initialization API Obsoleted in 1.91.5
+// font_srv_cpu_desc_handle and font_srv_gpu_desc_handle are handles to a single SRV descriptor to use for the internal font texture, they must be in 'srv_descriptor_heap'
+IMGUI_IMPL_API bool     ImGui_ImplDX12_Init(ID3D12Device* device, int num_frames_in_flight, DXGI_FORMAT rtv_format, ID3D12DescriptorHeap* srv_descriptor_heap, D3D12_CPU_DESCRIPTOR_HANDLE font_srv_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE font_srv_gpu_desc_handle);
+#endif
+
 // Use if you want to reset your rendering device without losing Dear ImGui state.
 IMGUI_IMPL_API bool     ImGui_ImplDX12_CreateDeviceObjects();
 IMGUI_IMPL_API void     ImGui_ImplDX12_InvalidateDeviceObjects();

docs/CHANGELOG.txt

@@ -41,10 +41,20 @@ HOW TO UPDATE?
 
 Breaking changes:
 
+- Backends: DX12: Changed ImGui_ImplDX12_Init() signature to take a
+  ImGui_ImplDX12_InitInfo struct.
+  - Using the new API, application is now required to pass function pointers
+    to allocate/free SRV Descriptors.
+  - We provide convenience legacy fields to pass a single descriptor,
+    matching the old API, but upcoming features will want multiple.
+  - Legacy ImGui_ImplDX12_Init() signature is still supported (will obsolete).
+
 Other changes:
 
 - Error Handling: fixed cases where recoverable error handling would crash when 
   processing errors outside of the NewFrame()..EndFrame() scope. (#1651)
+- Examples: Win32+DX12: Using a basic free-list allocator to manage multiple
+  SRV descriptors.
 
 
 -----------------------------------------------------------------------

examples/example_win32_directx12/main.cpp

@@ -25,20 +25,67 @@
 // Config for example app
 static const int APP_NUM_FRAMES_IN_FLIGHT = 3;
 static const int APP_NUM_BACK_BUFFERS = 3;
+static const int APP_SRV_HEAP_SIZE = 64;
 
 struct FrameContext
 {
     ID3D12CommandAllocator*     CommandAllocator;
     UINT64                      FenceValue;
 };
 
+// Simple free list based allocator
+struct ExampleDescriptorHeapAllocator
+{
+    ID3D12DescriptorHeap*       Heap = nullptr;
+    D3D12_DESCRIPTOR_HEAP_TYPE  HeapType = D3D12_DESCRIPTOR_HEAP_TYPE_NUM_TYPES;
+    D3D12_CPU_DESCRIPTOR_HANDLE HeapStartCpu;
+    D3D12_GPU_DESCRIPTOR_HANDLE HeapStartGpu;
+    UINT                        HeapHandleIncrement;
+    ImVector<int>               FreeIndices;
+
+    void Create(ID3D12Device* device, ID3D12DescriptorHeap* heap)
+    {
+        IM_ASSERT(Heap == nullptr && FreeIndices.empty());
+        Heap = heap;
+        D3D12_DESCRIPTOR_HEAP_DESC desc = heap->GetDesc();
+        HeapType = desc.Type;
+        HeapStartCpu = Heap->GetCPUDescriptorHandleForHeapStart();
+        HeapStartGpu = Heap->GetGPUDescriptorHandleForHeapStart();
+        HeapHandleIncrement = device->GetDescriptorHandleIncrementSize(HeapType);
+        FreeIndices.reserve((int)desc.NumDescriptors);
+        for (int n = desc.NumDescriptors; n > 0; n--)
+            FreeIndices.push_back(n);
+    }
+    void Destroy()
+    {
+        Heap = NULL;
+        FreeIndices.clear();
+    }
+    void Alloc(D3D12_CPU_DESCRIPTOR_HANDLE* out_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE* out_gpu_desc_handle)
+    {
+        IM_ASSERT(FreeIndices.Size > 0);
+        int idx = FreeIndices.back();
+        FreeIndices.pop_back();
+        out_cpu_desc_handle->ptr = HeapStartCpu.ptr + (idx * HeapHandleIncrement);
+        out_gpu_desc_handle->ptr = HeapStartGpu.ptr + (idx * HeapHandleIncrement);
+    }
+    void Free(D3D12_CPU_DESCRIPTOR_HANDLE out_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE out_gpu_desc_handle)
+    {
+        int cpu_idx = (int)((out_cpu_desc_handle.ptr - HeapStartCpu.ptr) / HeapHandleIncrement);
+        int gpu_idx = (int)((out_gpu_desc_handle.ptr - HeapStartGpu.ptr) / HeapHandleIncrement);
+        IM_ASSERT(cpu_idx == gpu_idx);
+        FreeIndices.push_back(cpu_idx);
+    }
+};
+
 // Data
 static FrameContext                 g_frameContext[APP_NUM_FRAMES_IN_FLIGHT] = {};
 static UINT                         g_frameIndex = 0;
 
 static ID3D12Device*                g_pd3dDevice = nullptr;
 static ID3D12DescriptorHeap*        g_pd3dRtvDescHeap = nullptr;
 static ID3D12DescriptorHeap*        g_pd3dSrvDescHeap = nullptr;
+static ExampleDescriptorHeapAllocator g_pd3dSrvDescHeapAlloc;
 static ID3D12CommandQueue*          g_pd3dCommandQueue = nullptr;
 static ID3D12GraphicsCommandList*   g_pd3dCommandList = nullptr;
 static ID3D12Fence*                 g_fence = nullptr;
@@ -93,10 +140,18 @@ int main(int, char**)
 
     // Setup Platform/Renderer backends
     ImGui_ImplWin32_Init(hwnd);
-    ImGui_ImplDX12_Init(g_pd3dDevice, NUM_FRAMES_IN_FLIGHT,
-        DXGI_FORMAT_R8G8B8A8_UNORM, g_pd3dSrvDescHeap,
-        g_pd3dSrvDescHeap->GetCPUDescriptorHandleForHeapStart(),
-        g_pd3dSrvDescHeap->GetGPUDescriptorHandleForHeapStart());
+
+    ImGui_ImplDX12_InitInfo init_info = {};
+    init_info.Device = g_pd3dDevice;
+    init_info.CommandQueue = g_pd3dCommandQueue;
+    init_info.NumFramesInFlight = APP_NUM_FRAMES_IN_FLIGHT;
+    init_info.RTVFormat = DXGI_FORMAT_R8G8B8A8_UNORM;
+    // Allocating SRV descriptors (for textures) is up to the application, so we provide callbacks.
+    // (current version of the backend will only allocate one descriptor, future versions will need to allocate more)
+    init_info.SrvDescriptorHeap = g_pd3dSrvDescHeap;
+    init_info.SrvDescriptorAllocFn = [](ImGui_ImplDX12_InitInfo*, D3D12_CPU_DESCRIPTOR_HANDLE* out_cpu_handle, D3D12_GPU_DESCRIPTOR_HANDLE* out_gpu_handle) { return g_pd3dSrvDescHeapAlloc.Alloc(out_cpu_handle, out_gpu_handle); };
+    init_info.SrvDescriptorFreeFn = [](ImGui_ImplDX12_InitInfo*, D3D12_CPU_DESCRIPTOR_HANDLE cpu_handle, D3D12_GPU_DESCRIPTOR_HANDLE gpu_handle)            { return g_pd3dSrvDescHeapAlloc.Free(cpu_handle, gpu_handle); };
+    ImGui_ImplDX12_Init(&init_info);
 
     // Load Fonts
     // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them.
@@ -310,10 +365,11 @@ bool CreateDeviceD3D(HWND hWnd)
     {
         D3D12_DESCRIPTOR_HEAP_DESC desc = {};
         desc.Type = D3D12_DESCRIPTOR_HEAP_TYPE_CBV_SRV_UAV;
-        desc.NumDescriptors = 1;
+        desc.NumDescriptors = APP_SRV_HEAP_SIZE;
         desc.Flags = D3D12_DESCRIPTOR_HEAP_FLAG_SHADER_VISIBLE;
         if (g_pd3dDevice->CreateDescriptorHeap(&desc, IID_PPV_ARGS(&g_pd3dSrvDescHeap)) != S_OK)
             return false;
+        g_pd3dSrvDescHeapAlloc.Create(g_pd3dDevice, g_pd3dSrvDescHeap);
     }
 
     {