Examples: DirectX12: Add directx12_example

examples/directx12_example/imgui_impl_dx12.h

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+// ImGui Win32 + DirectX12 binding
+// You can copy and use unmodified imgui_impl_* files in your project. See main.cpp for an example of using this.
+// If you use this binding you'll need to call 4 functions: ImGui_ImplXXXX_Init(), ImGui_ImplXXXX_NewFrame(), ImGui::Render() and ImGui_ImplXXXX_Shutdown().
+// If you are new to ImGui, see examples/README.txt and documentation at the top of imgui.cpp.
+// https://github.com/ocornut/imgui
+
+#include <d3d12.h>
+
+// cmdList is the command list that the implementation will use to render the
+// GUI.
+//
+// Before calling ImGui::Render(), caller must prepare cmdList by resetting it
+// and setting the appropriate render target and descriptor heap that contains
+// fontSrv*puDescHandle.
+//
+// fontSrvCpuDescHandle and fontSrvGpuDescHandle are handles to a single SRV
+// descriptor to use for the internal font texture.
+IMGUI_API bool        ImGui_ImplDX12_Init(void* hwnd, int numFramesInFlight,
+                                          ID3D12Device* device, ID3D12GraphicsCommandList* cmdList,
+                                          D3D12_CPU_DESCRIPTOR_HANDLE fontSrvCpuDescHandle,
+                                          D3D12_GPU_DESCRIPTOR_HANDLE fontSrvGpuDescHandle);
+IMGUI_API void        ImGui_ImplDX12_Shutdown();
+IMGUI_API void        ImGui_ImplDX12_NewFrame();
+
+// Use if you want to reset your rendering device without losing ImGui state.
+IMGUI_API void        ImGui_ImplDX12_InvalidateDeviceObjects();
+IMGUI_API bool        ImGui_ImplDX12_CreateDeviceObjects();
+
+// Handler for Win32 messages, update mouse/keyboard data.
+// You may or not need this for your implementation, but it can serve as reference for handling inputs.
+// Commented out to avoid dragging dependencies on <windows.h> types. You can copy the extern declaration in your code.
+/*
+IMGUI_API LRESULT   ImGui_ImplDX12_WndProcHandler(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);
+*/