ImGUI：基于 DirectX 12 的实现

ImGUI

ImGUI（Immediate Mode Graphical User Interface，即时模式图形用户界面）是一种区别于传统保留模式（Retained Mode）的 UI 开发范式。其核心思想是通过「每帧完全重建界面」的方式，将 UI 元素的创建、状态管理和用户交互响应紧密结合。开发者无需维护复杂的 UI 对象树，而是通过代码直接描述当前帧的界面状态，系统自动处理与上一帧的差异对比。

CMake

cmake_minimum_required(VERSION 3.10)
project(ImGUIgRPC VERSION 0.5)

set(CMAKE_CXX_STANDARD 14)

# ImGUI
set(IMGUI_DIR "${PROJECT_SOURCE_DIR}/ThirdParty/imgui-1.89.3")
include_directories(IMGUI_INCLUDES ${IMGUI_DIR} "${PROJECT_SOURCE_DIR}/ThirdParty/imgui-1.89.3/backends")
file (GLOB IMGUI_SRC ${IMGUI_DIR}/*.h ${IMGUI_DIR}/*.cpp)
file (GLOB PLATFORM_SRC ${IMGUI_DIR}/backends/imgui_impl_win32.* ${IMGUI_DIR}/backends/imgui_impl_dx12.*)

include_directories(${PROJECT_SOURCE_DIR}/include)
file (GLOB SRC_DIR ${PROJECT_SOURCE_DIR}/src/*.cpp)

add_executable(main ${SRC_DIR} ${IMGUI_SRC} ${PLATFORM_SRC})
target_link_libraries(main ${LIBS_NAME})
target_link_libraries(main
        d3d12.lib
        d3dcompiler.lib
        dxgi.lib
    )

重新封装的 DirectX 12 后端

主要是将官网的示例重新提取和封装到 dx12context.h 和 dx12context.cpp 中。

• 使用类重构
• 私有化类变量（getter）
• NULL 替换成 nullptr
• Impl 惯用法重构类

dx12context.h

#pragma once
#include <memory>

#include "imgui.h"
#include "imgui_impl_win32.h"
#include "imgui_impl_dx12.h"
#include <d3d12.h>
#include <dxgi1_4.h>
#include <tchar.h>

#ifdef _DEBUG
#define DX12_ENABLE_DEBUG_LAYER
#endif

#ifdef DX12_ENABLE_DEBUG_LAYER
#include <dxgidebug.h>
#pragma comment(lib, "dxguid.lib")
#endif

struct FrameContext
{
    ID3D12CommandAllocator *CommandAllocator;
    UINT64 FenceValue;
};

constexpr int NUM_FRAMES_IN_FLIGHT = 3;
constexpr int NUM_BACK_BUFFERS = 3;

class DX12Context
{
public:
    DX12Context();

    ~DX12Context();

    bool CreateDeviceD3D(HWND hWnd);

    void CleanupDeviceD3D();

    void CreateRenderTarget();

    void CleanupRenderTarget();

    void WaitForLastSubmittedFrame();

    FrameContext* WaitForNextFrameResources();

    FrameContext* frameContext();

    UINT frameIndex();

    void set_frameIndex(UINT index);

    ID3D12Device* pd3dDevice();

    ID3D12DescriptorHeap* pd3dRtvDescHeap();

    ID3D12DescriptorHeap* pd3dSrvDescHeap();

    ID3D12CommandQueue* pd3dCommandQueue();

    ID3D12GraphicsCommandList* pd3dCommandList();

    ID3D12Fence* fence();

    HANDLE fenceEvent();

    UINT64 fenceLastSignaledValue() const;

    void set_fenceLastSignaledValue(UINT64 value);

    IDXGISwapChain3* pSwapChain();

    void set_hSwapChainWaitableObject(HANDLE handle);

    HANDLE hSwapChainWaitableObject();

    D3D12_CPU_DESCRIPTOR_HANDLE* mainRenderTargetDescriptor();

    ID3D12Resource** mainRenderTargetResource();

private:
    struct Impl;
    std::unique_ptr<Impl> pImpl;
};

dx12context.cpp

#include "dx12context.h"

struct DX12Context::Impl {
    FrameContext frameContext_[NUM_FRAMES_IN_FLIGHT] = {};
    UINT frameIndex_ = 0;
    ID3D12Device* pd3dDevice_ = nullptr;
    ID3D12DescriptorHeap* pd3dRtvDescHeap_ = nullptr;
    ID3D12DescriptorHeap* pd3dSrvDescHeap_ = nullptr;
    ID3D12CommandQueue* pd3dCommandQueue_ = nullptr;
    ID3D12GraphicsCommandList* pd3dCommandList_ = nullptr;
    ID3D12Fence* fence_ = nullptr;
    HANDLE fenceEvent_ = nullptr;
    UINT64 fenceLastSignaledValue_ = 0;
    IDXGISwapChain3* pSwapChain_ = nullptr;
    HANDLE hSwapChainWaitableObject_ = nullptr;
    ID3D12Resource* mainRenderTargetResource_[NUM_BACK_BUFFERS] = {};
    D3D12_CPU_DESCRIPTOR_HANDLE mainRenderTargetDescriptor_[NUM_BACK_BUFFERS] = {};
};

DX12Context::DX12Context()
    : pImpl{std::make_unique<Impl>()}
{
}

DX12Context::~DX12Context()
{
}

bool DX12Context::CreateDeviceD3D(HWND hWnd)
{
    // Setup swap chain
    DXGI_SWAP_CHAIN_DESC1 sd;
    {
        ZeroMemory(&sd, sizeof(sd));
        sd.BufferCount = NUM_BACK_BUFFERS;
        sd.Width = 0;
        sd.Height = 0;
        sd.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
        sd.Flags = DXGI_SWAP_CHAIN_FLAG_FRAME_LATENCY_WAITABLE_OBJECT;
        sd.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;
        sd.SampleDesc.Count = 1;
        sd.SampleDesc.Quality = 0;
        sd.SwapEffect = DXGI_SWAP_EFFECT_FLIP_DISCARD;
        sd.AlphaMode = DXGI_ALPHA_MODE_UNSPECIFIED;
        sd.Scaling = DXGI_SCALING_STRETCH;
        sd.Stereo = FALSE;
    }

    // [DEBUG] Enable debug interface
#ifdef DX12_ENABLE_DEBUG_LAYER
    ID3D12Debug* pdx12Debug = nullptr;
    if (SUCCEEDED(D3D12GetDebugInterface(IID_PPV_ARGS(&pdx12Debug))))
        pdx12Debug->EnableDebugLayer();
#endif

    // Create device
    D3D_FEATURE_LEVEL featureLevel = D3D_FEATURE_LEVEL_11_0;
    if (D3D12CreateDevice(nullptr, featureLevel, IID_PPV_ARGS(&pImpl->pd3dDevice_)) != S_OK)
        return false;

    // [DEBUG] Setup debug interface to break on any warnings/errors
#ifdef DX12_ENABLE_DEBUG_LAYER
    if (pdx12Debug != nullptr)
    {
        ID3D12InfoQueue* pInfoQueue = nullptr;
        pImpl->pd3dDevice_->QueryInterface(IID_PPV_ARGS(&pInfoQueue));
        pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_ERROR, true);
        pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_CORRUPTION, true);
        pInfoQueue->SetBreakOnSeverity(D3D12_MESSAGE_SEVERITY_WARNING, true);
        pInfoQueue->Release();
        pdx12Debug->Release();
    }
#endif

    {
        D3D12_DESCRIPTOR_HEAP_DESC desc = {};
        desc.Type = D3D12_DESCRIPTOR_HEAP_TYPE_RTV;
        desc.NumDescriptors = NUM_BACK_BUFFERS;
        desc.Flags = D3D12_DESCRIPTOR_HEAP_FLAG_NONE;
        desc.NodeMask = 1;
        if (pImpl->pd3dDevice_->CreateDescriptorHeap(&desc, IID_PPV_ARGS(&pImpl->pd3dRtvDescHeap_)) != S_OK)
            return false;

        SIZE_T rtvDescriptorSize = pImpl->pd3dDevice_->GetDescriptorHandleIncrementSize(D3D12_DESCRIPTOR_HEAP_TYPE_RTV);
        D3D12_CPU_DESCRIPTOR_HANDLE rtvHandle = pImpl->pd3dRtvDescHeap_->GetCPUDescriptorHandleForHeapStart();
        for (UINT i = 0; i < NUM_BACK_BUFFERS; i++)
        {
            mainRenderTargetDescriptor()[i] = rtvHandle;
            rtvHandle.ptr += rtvDescriptorSize;
        }
    }

    {
        D3D12_DESCRIPTOR_HEAP_DESC desc = {};
        desc.Type = D3D12_DESCRIPTOR_HEAP_TYPE_CBV_SRV_UAV;
        desc.NumDescriptors = 1;
        desc.Flags = D3D12_DESCRIPTOR_HEAP_FLAG_SHADER_VISIBLE;
        if (pImpl->pd3dDevice_->CreateDescriptorHeap(&desc, IID_PPV_ARGS(&pImpl->pd3dSrvDescHeap_)) != S_OK)
            return false;
    }

    {
        D3D12_COMMAND_QUEUE_DESC desc = {};
        desc.Type = D3D12_COMMAND_LIST_TYPE_DIRECT;
        desc.Flags = D3D12_COMMAND_QUEUE_FLAG_NONE;
        desc.NodeMask = 1;
        if (pImpl->pd3dDevice_->CreateCommandQueue(&desc, IID_PPV_ARGS(&pImpl->pd3dCommandQueue_)) != S_OK)
            return false;
    }

    for (UINT i = 0; i < NUM_FRAMES_IN_FLIGHT; i++)
        if (pImpl->pd3dDevice_->CreateCommandAllocator(D3D12_COMMAND_LIST_TYPE_DIRECT, IID_PPV_ARGS(&pImpl->frameContext_[i].CommandAllocator)) != S_OK)
            return false;

    if (pImpl->pd3dDevice_->CreateCommandList(0, D3D12_COMMAND_LIST_TYPE_DIRECT, pImpl->frameContext_[0].CommandAllocator, nullptr, IID_PPV_ARGS(&pImpl->pd3dCommandList_)) != S_OK ||
        pImpl->pd3dCommandList_->Close() != S_OK)
        return false;

    if (pImpl->pd3dDevice_->CreateFence(0, D3D12_FENCE_FLAG_NONE, IID_PPV_ARGS(&pImpl->fence_)) != S_OK)
        return false;

    pImpl->fenceEvent_ = CreateEvent(nullptr, FALSE, FALSE, nullptr);
    if (pImpl->fenceEvent_ == nullptr)
        return false;

    {
        IDXGIFactory4* dxgiFactory = nullptr;
        IDXGISwapChain1* swapChain1 = nullptr;
        if (CreateDXGIFactory1(IID_PPV_ARGS(&dxgiFactory)) != S_OK)
            return false;
        if (dxgiFactory->CreateSwapChainForHwnd(pImpl->pd3dCommandQueue_, hWnd, &sd, nullptr, nullptr, &swapChain1) != S_OK)
            return false;
        if (swapChain1->QueryInterface(IID_PPV_ARGS(&pImpl->pSwapChain_)) != S_OK)
            return false;
        swapChain1->Release();
        dxgiFactory->Release();
        pImpl->pSwapChain_->SetMaximumFrameLatency(NUM_BACK_BUFFERS);
        set_hSwapChainWaitableObject(pImpl->pSwapChain_->GetFrameLatencyWaitableObject());
    }

    CreateRenderTarget();
    return true;
}

void DX12Context::CleanupDeviceD3D()
{
    CleanupRenderTarget();
    if (pImpl->pSwapChain_)
    {
        pImpl->pSwapChain_->SetFullscreenState(false, nullptr);
        pImpl->pSwapChain_->Release();
        pImpl->pSwapChain_ = nullptr;
    }
    if (hSwapChainWaitableObject() != nullptr)
    {
        CloseHandle(hSwapChainWaitableObject());
    }
    for (UINT i = 0; i < NUM_FRAMES_IN_FLIGHT; i++)
        if (pImpl->frameContext_[i].CommandAllocator)
        {
            pImpl->frameContext_[i].CommandAllocator->Release();
            pImpl->frameContext_[i].CommandAllocator = nullptr;
        }
    if (pImpl->pd3dCommandQueue_)
    {
        pImpl->pd3dCommandQueue_->Release();
        pImpl->pd3dCommandQueue_ = nullptr;
    }
    if (pImpl->pd3dCommandList_)
    {
        pImpl->pd3dCommandList_->Release();
        pImpl->pd3dCommandList_ = nullptr;
    }
    if (pImpl->pd3dRtvDescHeap_)
    {
        pImpl->pd3dRtvDescHeap_->Release();
        pImpl->pd3dRtvDescHeap_ = nullptr;
    }
    if (pImpl->pd3dSrvDescHeap_)
    {
        pImpl->pd3dSrvDescHeap_->Release();
        pImpl->pd3dSrvDescHeap_ = nullptr;
    }
    if (pImpl->fence_)
    {
        pImpl->fence_->Release();
        pImpl->fence_ = nullptr;
    }
    if (pImpl->fenceEvent_)
    {
        CloseHandle(pImpl->fenceEvent_);
        pImpl->fenceEvent_ = nullptr;
    }
    if (pImpl->pd3dDevice_)
    {
        pImpl->pd3dDevice_->Release();
        pImpl->pd3dDevice_ = nullptr;
    }

#ifdef DX12_ENABLE_DEBUG_LAYER
    IDXGIDebug1* pDebug = nullptr;
    if (SUCCEEDED(DXGIGetDebugInterface1(0, IID_PPV_ARGS(&pDebug))))
    {
        pDebug->ReportLiveObjects(DXGI_DEBUG_ALL, DXGI_DEBUG_RLO_SUMMARY);
        pDebug->Release();
    }
#endif
}

void DX12Context::CreateRenderTarget()
{
    for (UINT i = 0; i < NUM_BACK_BUFFERS; i++)
    {
        ID3D12Resource* pBackBuffer = nullptr;
        pImpl->pSwapChain_->GetBuffer(i, IID_PPV_ARGS(&pBackBuffer));
        pImpl->pd3dDevice_->CreateRenderTargetView(pBackBuffer, nullptr, mainRenderTargetDescriptor()[i]);
        mainRenderTargetResource()[i] = pBackBuffer;
    }
}

void DX12Context::CleanupRenderTarget()
{
    WaitForLastSubmittedFrame();

    for (UINT i = 0; i < NUM_BACK_BUFFERS; i++)
    {
        if (mainRenderTargetResource()[i])
        {
            mainRenderTargetResource()[i]->Release();
            mainRenderTargetResource()[i] = nullptr;
        }
    }
}

void DX12Context::WaitForLastSubmittedFrame()
{
    FrameContext* frameCtx = &pImpl->frameContext_[pImpl->frameIndex_ % NUM_FRAMES_IN_FLIGHT];

    UINT64 fenceValue = frameCtx->FenceValue;
    if (fenceValue == 0)
        return; // No fence was signaled

    frameCtx->FenceValue = 0;
    if (pImpl->fence_->GetCompletedValue() >= fenceValue)
        return;

    pImpl->fence_->SetEventOnCompletion(fenceValue, pImpl->fenceEvent_);
    WaitForSingleObject(pImpl->fenceEvent_, INFINITE);
}


FrameContext* DX12Context::WaitForNextFrameResources()
{
    UINT nextFrameIndex = pImpl->frameIndex_ + 1;
    pImpl->frameIndex_ = nextFrameIndex;

    HANDLE waitableObjects[] = { hSwapChainWaitableObject(), nullptr};
    DWORD numWaitableObjects = 1;

    FrameContext* frameCtx = &pImpl->frameContext_[nextFrameIndex % NUM_FRAMES_IN_FLIGHT];
    UINT64 fenceValue = frameCtx->FenceValue;
    if (fenceValue != 0) // means no fence was signaled
    {
        frameCtx->FenceValue = 0;
        pImpl->fence_->SetEventOnCompletion(fenceValue, pImpl->fenceEvent_);
        waitableObjects[1] = pImpl->fenceEvent_;
        numWaitableObjects = 2;
    }

    WaitForMultipleObjects(numWaitableObjects, waitableObjects, TRUE, INFINITE);

    return frameCtx;
}

FrameContext* DX12Context::frameContext() {
    return pImpl->frameContext_;
}

UINT DX12Context::frameIndex() {
    return pImpl->frameIndex_;
}

void DX12Context::set_frameIndex(UINT index) {
    pImpl->frameIndex_ = index;
}

ID3D12Device* DX12Context::pd3dDevice() {
    return pImpl->pd3dDevice_;
}

ID3D12DescriptorHeap* DX12Context::pd3dRtvDescHeap() {
    return pImpl->pd3dRtvDescHeap_;
}

ID3D12DescriptorHeap* DX12Context::pd3dSrvDescHeap() {
    return pImpl->pd3dSrvDescHeap_;
}

ID3D12CommandQueue* DX12Context::pd3dCommandQueue() {
    return pImpl->pd3dCommandQueue_;
}

ID3D12GraphicsCommandList* DX12Context::pd3dCommandList() {
    return pImpl->pd3dCommandList_;
}

ID3D12Fence* DX12Context::fence() {
    return pImpl->fence_;
}

HANDLE DX12Context::fenceEvent() {
    return pImpl->fenceEvent_;
}

UINT64 DX12Context::fenceLastSignaledValue() const {
    return pImpl->fenceLastSignaledValue_;
}

void DX12Context::set_fenceLastSignaledValue(UINT64 value) {
    pImpl->fenceLastSignaledValue_ = value;
}

IDXGISwapChain3* DX12Context::pSwapChain() {
    return pImpl->pSwapChain_;
}

void DX12Context::set_hSwapChainWaitableObject(HANDLE handle) {
    pImpl->hSwapChainWaitableObject_ = handle;
}

HANDLE DX12Context::hSwapChainWaitableObject() {
    return pImpl->hSwapChainWaitableObject_;
}

D3D12_CPU_DESCRIPTOR_HANDLE* DX12Context::mainRenderTargetDescriptor() {
    return pImpl->mainRenderTargetDescriptor_;
}

ID3D12Resource** DX12Context::mainRenderTargetResource() {
    return pImpl->mainRenderTargetResource_;
}

main

// Dear ImGui: standalone example application for DirectX 12
// If you are new to Dear ImGui, read documentation from the docs/ folder + read the top of imgui.cpp.
// Read online: https://github.com/ocornut/imgui/tree/master/docs

// Important: to compile on 32-bit systems, the DirectX12 backend requires code to be compiled with '#define ImTextureID ImU64'.
// This is because we need ImTextureID to carry a 64-bit value and by default ImTextureID is defined as void*.
// This define is set in the example .vcxproj file and need to be replicated in your app or by adding it to your imconfig.h file.
#include "dx12context.h"

static DX12Context ctx;

LRESULT WINAPI WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);

// Main code
int main(int, char **)
{
    // Create application window
    // ImGui_ImplWin32_EnableDpiAwareness();
    WNDCLASSEXW wc = {sizeof(wc), CS_CLASSDC, WndProc, 0L, 0L, GetModuleHandle(nullptr), nullptr, nullptr, nullptr, nullptr, L"ImGui Example", nullptr};
    ::RegisterClassExW(&wc);
    HWND hwnd = ::CreateWindowW(wc.lpszClassName, L"Dear ImGui DirectX12 Example", WS_OVERLAPPEDWINDOW, 100, 100, 1280, 800, nullptr, nullptr, wc.hInstance, nullptr);

    // Initialize Direct3D
    if (!ctx.CreateDeviceD3D(hwnd))
    {
        ctx.CleanupDeviceD3D();
        ::UnregisterClassW(wc.lpszClassName, wc.hInstance);
        return 1;
    }

    // Show the window
    ::ShowWindow(hwnd, SW_SHOWDEFAULT);
    ::UpdateWindow(hwnd);

    // Setup Dear ImGui context
    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGuiIO &io = ImGui::GetIO();
    (void)io;
    io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard; // Enable Keyboard Controls
    io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;  // Enable Gamepad Controls

    // Setup Dear ImGui style
    ImGui::StyleColorsDark();
    // ImGui::StyleColorsLight();

    // Setup Platform/Renderer backends
    ImGui_ImplWin32_Init(hwnd);
    ImGui_ImplDX12_Init(ctx.pd3dDevice(), NUM_FRAMES_IN_FLIGHT,
                        DXGI_FORMAT_R8G8B8A8_UNORM, ctx.pd3dSrvDescHeap(),
                        ctx.pd3dSrvDescHeap()->GetCPUDescriptorHandleForHeapStart(),
                        ctx.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.
    // - If the file cannot be loaded, the function will return nullptr. Please handle those errors in your application (e.g. use an assertion, or display an error and quit).
    // - The fonts will be rasterized at a given size (w/ oversampling) and stored into a texture when calling ImFontAtlas::Build()/GetTexDataAsXXXX(), which ImGui_ImplXXXX_NewFrame below will call.
    // - Use '#define IMGUI_ENABLE_FREETYPE' in your imconfig file to use Freetype for higher quality font rendering.
    // - Read 'docs/FONTS.md' for more instructions and details.
    // - Remember that in C/C++ if you want to include a backslash \ in a string literal you need to write a double backslash \\ !
    // io.Fonts->AddFontDefault();
    // io.Fonts->AddFontFromFileTTF("c:\\Windows\\Fonts\\segoeui.ttf", 18.0f);
    // io.Fonts->AddFontFromFileTTF("../../misc/fonts/DroidSans.ttf", 16.0f);
    // io.Fonts->AddFontFromFileTTF("../../misc/fonts/Roboto-Medium.ttf", 16.0f);
    // io.Fonts->AddFontFromFileTTF("../../misc/fonts/Cousine-Regular.ttf", 15.0f);
    // ImFont* font = io.Fonts->AddFontFromFileTTF("c:\\Windows\\Fonts\\ArialUni.ttf", 18.0f, nullptr, io.Fonts->GetGlyphRangesJapanese());
    // IM_ASSERT(font != nullptr);

    // Our state
    bool show_demo_window = true;
    bool show_another_window = false;
    ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);

    // Main loop
    bool done = false;
    while (!done)
    {
        // Poll and handle messages (inputs, window resize, etc.)
        // See the WndProc() function below for our to dispatch events to the Win32 backend.
        MSG msg;
        while (::PeekMessage(&msg, nullptr, 0U, 0U, PM_REMOVE))
        {
            ::TranslateMessage(&msg);
            ::DispatchMessage(&msg);
            if (msg.message == WM_QUIT)
                done = true;
        }
        if (done)
            break;

        // Start the Dear ImGui frame
        ImGui_ImplDX12_NewFrame();
        ImGui_ImplWin32_NewFrame();
        ImGui::NewFrame();

        // 1. Show the big demo window (Most of the sample code is in ImGui::ShowDemoWindow()! You can browse its code to learn more about Dear ImGui!).
        if (show_demo_window)
            ImGui::ShowDemoWindow(&show_demo_window);

        // 2. Show a simple window that we create ourselves. We use a Begin/End pair to create a named window.
        {
            float f = 0.0f;
            int counter = 0;

            ImGui::Begin("Hello, world!"); // Create a window called "Hello, world!" and append into it.

            ImGui::Text("This is some useful text.");          // Display some text (you can use a format strings too)
            ImGui::Checkbox("Demo Window", &show_demo_window); // Edit bools storing our window open/close state
            ImGui::Checkbox("Another Window", &show_another_window);

            ImGui::SliderFloat("float", &f, 0.0f, 1.0f);             // Edit 1 float using a slider from 0.0f to 1.0f
            ImGui::ColorEdit3("clear color", (float *)&clear_color); // Edit 3 floats representing a color

            if (ImGui::Button("Button")) // Buttons return true when clicked (most widgets return true when edited/activated)
                counter++;
            ImGui::SameLine();
            ImGui::Text("counter = %d", counter);

            ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / io.Framerate, io.Framerate);
            ImGui::End();
        }

        // 3. Show another simple window.
        if (show_another_window)
        {
            ImGui::Begin("Another Window", &show_another_window); // Pass a pointer to our bool variable (the window will have a closing button that will clear the bool when clicked)
            ImGui::Text("Hello from another window!");
            if (ImGui::Button("Close Me"))
                show_another_window = false;
            ImGui::End();
        }

        // Rendering
        ImGui::Render();

        FrameContext *frameCtx = ctx.WaitForNextFrameResources();
        UINT backBufferIdx = ctx.pSwapChain()->GetCurrentBackBufferIndex();
        frameCtx->CommandAllocator->Reset();

        D3D12_RESOURCE_BARRIER barrier = {};
        barrier.Type = D3D12_RESOURCE_BARRIER_TYPE_TRANSITION;
        barrier.Flags = D3D12_RESOURCE_BARRIER_FLAG_NONE;
        barrier.Transition.pResource = ctx.mainRenderTargetResource()[backBufferIdx];
        barrier.Transition.Subresource = D3D12_RESOURCE_BARRIER_ALL_SUBRESOURCES;
        barrier.Transition.StateBefore = D3D12_RESOURCE_STATE_PRESENT;
        barrier.Transition.StateAfter = D3D12_RESOURCE_STATE_RENDER_TARGET;
        ctx.pd3dCommandList()->Reset(frameCtx->CommandAllocator, nullptr);
        ctx.pd3dCommandList()->ResourceBarrier(1, &barrier);

        // Render Dear ImGui graphics
        const float clear_color_with_alpha[4] = {clear_color.x * clear_color.w, clear_color.y * clear_color.w, clear_color.z * clear_color.w, clear_color.w};
        ctx.pd3dCommandList()->ClearRenderTargetView(ctx.mainRenderTargetDescriptor()[backBufferIdx], clear_color_with_alpha, 0, nullptr);
        ctx.pd3dCommandList()->OMSetRenderTargets(1, &ctx.mainRenderTargetDescriptor()[backBufferIdx], FALSE, nullptr);
        auto srvDescHeap = ctx.pd3dSrvDescHeap();
        ctx.pd3dCommandList()->SetDescriptorHeaps(1, &srvDescHeap);
        ImGui_ImplDX12_RenderDrawData(ImGui::GetDrawData(), ctx.pd3dCommandList());
        barrier.Transition.StateBefore = D3D12_RESOURCE_STATE_RENDER_TARGET;
        barrier.Transition.StateAfter = D3D12_RESOURCE_STATE_PRESENT;
        ctx.pd3dCommandList()->ResourceBarrier(1, &barrier);
        ctx.pd3dCommandList()->Close();
        auto cmdList = ctx.pd3dCommandList();
        ctx.pd3dCommandQueue()->ExecuteCommandLists(1, (ID3D12CommandList* const*)&cmdList);

        ctx.pSwapChain()->Present(1, 0); // Present with vsync
        // ctx.pSwapChain->Present(0, 0); // Present without vsync

        UINT64 fenceValue = ctx.fenceLastSignaledValue() + 1;
        ctx.pd3dCommandQueue()->Signal(ctx.fence(), fenceValue);
        ctx.set_fenceLastSignaledValue(fenceValue);
        frameCtx->FenceValue = fenceValue;
    }

    ctx.WaitForLastSubmittedFrame();

    // Cleanup
    ImGui_ImplDX12_Shutdown();
    ImGui_ImplWin32_Shutdown();
    ImGui::DestroyContext();

    ctx.CleanupDeviceD3D();
    ::DestroyWindow(hwnd);
    ::UnregisterClassW(wc.lpszClassName, wc.hInstance);

    return 0;
}

// Forward declare message handler from imgui_impl_win32.cpp
extern IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);

// Win32 message handler
// You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
// - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application, or clear/overwrite your copy of the mouse data.
// - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application, or clear/overwrite your copy of the keyboard data.
// Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
LRESULT WINAPI WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    if (ImGui_ImplWin32_WndProcHandler(hWnd, msg, wParam, lParam))
        return true;

    switch (msg)
    {
    case WM_SIZE:
        if (ctx.pd3dDevice() != nullptr && wParam != SIZE_MINIMIZED)
        {
            ctx.WaitForLastSubmittedFrame();
            ctx.CleanupRenderTarget();
            HRESULT result = ctx.pSwapChain()->ResizeBuffers(0, (UINT)LOWORD(lParam), (UINT)HIWORD(lParam), DXGI_FORMAT_UNKNOWN, DXGI_SWAP_CHAIN_FLAG_FRAME_LATENCY_WAITABLE_OBJECT);
            assert(SUCCEEDED(result) && "Failed to resize swapchain.");
            ctx.CreateRenderTarget();
        }
        return 0;
    case WM_SYSCOMMAND:
        if ((wParam & 0xfff0) == SC_KEYMENU) // Disable ALT application menu
            return 0;
        break;
    case WM_DESTROY:
        ::PostQuitMessage(0);
        return 0;
    }
    return ::DefWindowProcW(hWnd, msg, wParam, lParam);
}

替换成中文字体

ImFont* font = io.Fonts->AddFontFromFileTTF("FangSong.ttf", 16.0f, nullptr, io.Fonts->GetGlyphRangesChineseSimplifiedCommon());
IM_ASSERT(font != nullptr);

目前，新的 Visual Studio 应该都是默认 UTF8 了，不一定需要在字符串前面使用 u8。

GetGlyphRangesChineseSimplifiedCommon 只是包含中文常用字，如果发现有的汉字显示不了，变成了 ?，可以改用 GetGlyphRangesChineseFull。不过，加载的字多了之后，肯定会额外消耗内存。

嵌入字体

依赖外部字体文件在进行程序的分发后其实很容易丢失文件，而字体又是界面 UI 的基础。可以考虑将字体直接嵌入到程序之中，而不是从外部文件中进行读取，从而不再依赖外部字体文件，避免字体丢失。ImGUI 提供了 AddFontFromMemoryTTF 支持这一操作。

可以通过将二进制转换成 C/C++ 的工具，例如 bin2c 将字体转换成 C/C++ 字节数组。

ImFontConfig fontConfig;
fontConfig.FontDataOwnedByAtlas = false;

ImFont* font = io.Fonts->AddFontFromMemoryTTF((void*)(FangSongFontData), sizeof(FangSongFontData), 16.0f, &fontConfig, io.Fonts->GetGlyphRangesChineseFull());
IM_ASSERT(font != nullptr);

这里需要注意内存所有权的问题，由于转换的 C++ 数组的类型类似 static const unsigned char FangSongFontData[12434444UL + 1]，而 AddFontFromMemoryTTF 默认会移交内存所有权，这样最后会进行 delete。所以需要通过设置 FontDataOwnedByAtlas = false 明确内存所有权，避免进行内存清理导致错误。

嵌入字体会让最终生成的可执行文件变大，而且动辄十几甚至几十 MB 的字体保存到纯文本的(.cpp)中，打开效率也会受到影响。

铺满窗口

如果显然 Begin 和 End 定义的小窗口铺满 Windows 窗口，可以按窗口大小设置，并禁止移动和改变大小，这样可以获得和传统应用类似的体验。

ImGui::SetNextWindowSize(ImGui::GetIO().DisplaySize);
ImGui::SetNextWindowPos(ImVec2(0, 0));

ImGui::Begin("Hello, world!", nullptr, ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoResize);

获取相对路径的工具函数

用一个按钮给用户选择文件的时候，打开 Windows 的文件对话框。

#include <iostream>
#include <string>
#include <filesystem>

namespace fs = std::filesystem;

void ReadFilePath(std::string& filePath, const char* filter)
{
    char fileName[MAX_PATH] = { 0 };
    OPENFILENAMEA ofn;
    ZeroMemory(&ofn, sizeof(ofn));

    ofn.lStructSize = sizeof(ofn);
    ofn.lpstrFilter = filter;
    ofn.lpstrFile = fileName;
    ofn.nMaxFile = MAX_PATH;
    ofn.Flags = OFN_EXPLORER | OFN_FILEMUSTEXIST | OFN_HIDEREADONLY | OFN_NOCHANGEDIR;

    if (GetOpenFileNameA(&ofn))
    {
        fs::path fullFilePath = ofn.lpstrFile;
        fs::path programPath = fs::current_path();

        // 使用filesystem库计算相对路径
        std::string relativePath = fs::proximate(fullFilePath, programPath).generic_string();

        // 如果是相对路径,则保留相对路径
        if (!relativePath.empty() && relativePath != "." && relativePath != "..")
        {
            filePath = relativePath;
        }
        else
        {
            // 否则,记录完整路径
            filePath = fullFilePath.generic_string();
        }
    }
}

小结

好吧，其实最初原本是想在这个基础上学习 DirectX 12 的。然后？就一直还没有然后。