Backends: DX12: comment about using SrvDescriptorAllocFn/SrvDescriptorFreeFn.

Amend 40b2286

Author: ocornut

backends/imgui_impl_dx12.cpp

@@ -748,7 +748,7 @@ bool ImGui_ImplDX12_Init(ImGui_ImplDX12_InitInfo* init_info)
         init_info->SrvDescriptorAllocFn = [](ImGui_ImplDX12_InitInfo*, D3D12_CPU_DESCRIPTOR_HANDLE* out_cpu_handle, D3D12_GPU_DESCRIPTOR_HANDLE* out_gpu_handle)
         {
             ImGui_ImplDX12_Data* bd = ImGui_ImplDX12_GetBackendData();
-            IM_ASSERT(bd->LegacySingleDescriptorUsed == false);
+            IM_ASSERT(bd->LegacySingleDescriptorUsed == false && "Only 1 simultaneous texture allowed with legacy ImGui_ImplDX12_Init() signature!");
             *out_cpu_handle = bd->InitInfo.LegacySingleSrvCpuDescriptor;
             *out_gpu_handle = bd->InitInfo.LegacySingleSrvGpuDescriptor;
             bd->LegacySingleDescriptorUsed = true;

backends/imgui_impl_dx12.h

@@ -34,7 +34,7 @@ struct ImGui_ImplDX12_InitInfo
     void*                       UserData;
 
     // 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)
+    // (current version of the backend will only allocate one descriptor, from 1.92 the backend 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);

examples/example_win32_directx12/main.cpp

@@ -154,6 +154,9 @@ int main(int, char**)
     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);
 
+    // Before 1.91.6: our signature was using a single descriptor. From 1.92, specifying SrvDescriptorAllocFn/SrvDescriptorFreeFn will be required to benefit from new features.
+    //ImGui_ImplDX12_Init(g_pd3dDevice, APP_NUM_FRAMES_IN_FLIGHT, DXGI_FORMAT_R8G8B8A8_UNORM, g_pd3dSrvDescHeap, g_pd3dSrvDescHeap->GetCPUDescriptorHandleForHeapStart(), g_pd3dSrvDescHeap->GetGPUDescriptorHandleForHeapStart());
+
     // 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.
     // - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple.