Add standalone example application for Dear ImGui with DirectX 12 support

Author: DMsuDev

examples/ImGui/include/imgui/backends/imgui_impl_dx12.cpp

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+// dear imgui: Renderer Backend for DirectX12
+// This needs to be used along with a Platform Backend (e.g. Win32)
+
+// Implemented features:
+//  [X] Renderer: User texture binding. Use 'D3D12_GPU_DESCRIPTOR_HANDLE' as texture identifier. Read the FAQ about ImTextureID/ImTextureRef!
+//  [X] Renderer: Large meshes support (64k+ vertices) even with 16-bit indices (ImGuiBackendFlags_RendererHasVtxOffset).
+//  [X] Renderer: Texture updates support for dynamic font atlas (ImGuiBackendFlags_RendererHasTextures).
+//  [X] Renderer: Expose selected render state for draw callbacks to use. Access in '(ImGui_ImplXXXX_RenderState*)GetPlatformIO().Renderer_RenderState'.
+
+// The aim of imgui_impl_dx12.h/.cpp is to be usable in your engine without any modification.
+// IF YOU FEEL YOU NEED TO MAKE ANY CHANGE TO THIS CODE, please share them and your feedback at https://github.com/ocornut/imgui/
+
+// You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
+// Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
+// Learn about Dear ImGui:
+// - FAQ                  https://dearimgui.com/faq
+// - Getting Started      https://dearimgui.com/getting-started
+// - Documentation        https://dearimgui.com/docs (same as your local docs/ folder).
+// - Introduction, links and more at the top of imgui.cpp
+
+#pragma once
+#include "imgui.h"      // IMGUI_IMPL_API
+#ifndef IMGUI_DISABLE
+#include <dxgiformat.h> // DXGI_FORMAT
+#include <d3d12.h>      // D3D12_CPU_DESCRIPTOR_HANDLE
+
+// Initialization data, for ImGui_ImplDX12_Init()
+struct ImGui_ImplDX12_InitInfo
+{
+    ID3D12Device*               Device;
+    ID3D12CommandQueue*         CommandQueue;       // Command queue used for queuing texture uploads.
+    int                         NumFramesInFlight;
+    DXGI_FORMAT                 RTVFormat;          // RenderTarget format.
+    DXGI_FORMAT                 DSVFormat;          // DepthStencilView format.
+    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, 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);
+#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
+
+    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'
+// - When we introduced the ImGui_ImplDX12_InitInfo struct we also added a 'ID3D12CommandQueue* CommandQueue' field.
+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();
+
+// (Advanced) Use e.g. if you need to precisely control the timing of texture updates (e.g. for staged rendering), by setting ImDrawData::Textures = NULL to handle this manually.
+IMGUI_IMPL_API void     ImGui_ImplDX12_UpdateTexture(ImTextureData* tex);
+
+// [BETA] Selected render state data shared with callbacks.
+// This is temporarily stored in GetPlatformIO().Renderer_RenderState during the ImGui_ImplDX12_RenderDrawData() call.
+// (Please open an issue if you feel you need access to more data)
+struct ImGui_ImplDX12_RenderState
+{
+    ID3D12Device*               Device;
+    ID3D12GraphicsCommandList*  CommandList;
+};
+
+#endif // #ifndef IMGUI_DISABLE