DirectX11 ClearRenderTargetViewback透明缓冲

我试图创建一个使用directx在透明视图(即桌面显示通过)之上绘制不透明内容的窗口。使用DirectX11，我试图做以下事情，但它没有使背景透明。事实上，我输入的任何不透明度值都会得到相同的结果。

我在做什么:

float color[4] = { 0.0f, 0.0f, 0.0f, 0.0f };
deviceContext->ClearRenderTargetView(backBuffer, color);

工作重现代码(main.cpp):

#include <Windows.h>
#include <windowsx.h>
#pragma comment (lib, "Winmm.lib")
#include <d3d11.h>
#pragma comment (lib, "d3d11.lib")
#include <d3dcompiler.h>
#pragma comment(lib, "D3DCompiler.lib")
#include <dwmapi.h>
#pragma comment (lib, "Dwmapi.lib")

// Globals
IDXGISwapChain *swapChain;
ID3D11Device *device;
ID3D11DeviceContext *deviceContext;
ID3D11RenderTargetView *backBuffer;
ID3D11InputLayout *inputLayout;            // the pointer to the input layout
ID3D11VertexShader *vertexShader;               // the pointer to the vertex shader
ID3D11PixelShader *pixelShader;                // the pointer to the pixel shader
ID3D11Buffer *vertexBuffer;                // the pointer to the vertex buffer
void InitializeDirectX(HWND hWnd);
void LoadTriangle();
struct Vertex {
    float x, y, z;
    float color[4];
};
// this is the main message handler for the program
LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_DESTROY:
    {
                       // close the application entirely
                       PostQuitMessage(0);
                       return 0;
    }
    }
    return DefWindowProc(hWnd, message, wParam, lParam);
}
// Globals
const LPCWSTR ClassName = L"className";

// the entry point for any Windows program
int WINAPI WinMain(HINSTANCE hInstance,
    HINSTANCE hPrevInstance,
    LPSTR lpCmdLine,
    int nCmdShow)
{
    // the handle for the window, filled by a function
    HWND hWnd;
    // this struct holds information for the window class
    WNDCLASSEX wc;
    // Pick out window size
    int windowHeight = 400;
    int windowWidth = 400;
    // clear out the window class for use
    ZeroMemory(&wc, sizeof(WNDCLASSEX));
    // fill in the struct with the needed information
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = WindowProc;
    wc.hInstance = hInstance;
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)COLOR_WINDOW;
    wc.lpszClassName = ClassName;
    // register the window class
    RegisterClassEx(&wc);
    // Window style
    DWORD exStyle = WS_EX_LAYERED | WS_EX_TOPMOST;
    DWORD style = WS_POPUP;
    // create the window and use the result as the handle
    hWnd = CreateWindowEx(
        exStyle,        // extended styles
        ClassName,    // name of the window class
        L"TestOverlay",   // title of the window
        style,    // window style
        0,    // x-position of the window
        0,    // y-position of the window
        400,    // width of the window
        400,    // height of the window
        NULL,    // we have no parent window, NULL
        NULL,    // we aren't using menus, NULL
        hInstance,    // application handle
        NULL);    // used with multiple windows, NULL
    // display the window on the screen
    ShowWindow(hWnd, nCmdShow);
    SetWindowPos(hWnd,
        HWND_TOPMOST,
        0, 0,
        windowWidth, windowHeight,
        SWP_SHOWWINDOW);
    // Show the window
    ShowWindow(hWnd, SW_SHOWDEFAULT);
    UpdateWindow(hWnd);
    // Make the window transparent
    SetWindowLong(hWnd, GWL_EXSTYLE, WS_EX_LAYERED);
    SetLayeredWindowAttributes(hWnd, RGB(0, 0, 0), 255, LWA_ALPHA | LWA_COLORKEY);
    // NOTE: If I uncomment DwmExtendFrameIntoClientArea then it becomes transparent, otherwise its a black screen
    MARGINS dwmMargin = { -1 };
    //DwmExtendFrameIntoClientArea(hWnd, &dwmMargin);
    // DirectX
    InitializeDirectX(hWnd);
    LoadTriangle();
    // enter the main loop:
    MSG msg;
    BOOL gotMessage;
    while (TRUE)
    {
        if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
            if (msg.message == WM_QUIT)
                break;
            // DirectX stuff
            float color[4] = { 0.0f, 0.0f, 0.0f, 0.0f };
            deviceContext->ClearRenderTargetView(backBuffer, color);
            // Draw triangle
            UINT stride = sizeof(Vertex);
            UINT offset = 0;
            deviceContext->IASetVertexBuffers(0, 1, &vertexBuffer, &stride, &offset);
            deviceContext->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
            deviceContext->Draw(3, 0);
            swapChain->Present(0, 0);
        }
    }
    return msg.wParam;
}

void InitializeDirectX(HWND hWnd)
{
    // create a struct to hold information about the swap chain
    DXGI_SWAP_CHAIN_DESC scd;
    // clear out the struct for use
    ZeroMemory(&scd, sizeof(DXGI_SWAP_CHAIN_DESC));
    // fill the swap chain description struct
    scd.BufferCount = 1;                                    // one back buffer
    scd.BufferDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;     // use 32-bit color
    scd.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;      // how swap chain is to be used
    scd.OutputWindow = hWnd;                                // the window to be used
    scd.SampleDesc.Count = 4;                               // how many multisamples
    scd.Windowed = TRUE;                                    // windowed/full-screen mode
    // create a device, device context and swap chain using the information in the scd struct
    D3D11CreateDeviceAndSwapChain(NULL,
        D3D_DRIVER_TYPE_HARDWARE,
        NULL,
        NULL,
        NULL,
        NULL,
        D3D11_SDK_VERSION,
        &scd,
        &swapChain,
        &device,
        NULL,
        &deviceContext);

    // get the address of the back buffer
    ID3D11Texture2D *pBackBuffer;
    swapChain->GetBuffer(0, __uuidof(ID3D11Texture2D), (LPVOID*)&pBackBuffer);
    // use the back buffer address to create the render target
    device->CreateRenderTargetView(pBackBuffer, NULL, &backBuffer);
    pBackBuffer->Release();
    // set the render target as the back buffer
    deviceContext->OMSetRenderTargets(1, &backBuffer, NULL);
    // Set the viewport size
    RECT cRect;
    GetClientRect(hWnd, &cRect);
    D3D11_VIEWPORT viewport;
    ZeroMemory(&viewport, sizeof(D3D11_VIEWPORT));
    viewport.TopLeftX = 0;
    viewport.TopLeftY = 0;
    viewport.Width = cRect.right - cRect.left;
    viewport.Height = cRect.bottom - cRect.top;
    deviceContext->RSSetViewports(1, &viewport);

    // Initialize pipeline stuff
    ID3D10Blob *VS, *PS;
    // compile shader
    D3DCompileFromFile(L"shaders.shader", 0, 0, "VShader", "vs_4_0", 0, 0, &VS, 0);
    D3DCompileFromFile(L"shaders.shader", 0, 0, "PShader", "ps_4_0", 0, 0, &PS, 0);
    // encapsulate both shaders into shader objects
    device->CreateVertexShader(VS->GetBufferPointer(), VS->GetBufferSize(), NULL, &vertexShader);
    device->CreatePixelShader(PS->GetBufferPointer(), PS->GetBufferSize(), NULL, &pixelShader);
    deviceContext->VSSetShader(vertexShader, 0, 0);
    deviceContext->PSSetShader(pixelShader, 0, 0);
    // create input layout object
    D3D11_INPUT_ELEMENT_DESC ied[] =
    {
        { "POSITION", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 0, D3D11_INPUT_PER_VERTEX_DATA, 0 },
        { "COLOR", 0, DXGI_FORMAT_R32G32B32A32_FLOAT, 0, 12, D3D11_INPUT_PER_VERTEX_DATA, 0 },
    };
    device->CreateInputLayout(ied, 2, VS->GetBufferPointer(), VS->GetBufferSize(), &inputLayout);
    deviceContext->IASetInputLayout(inputLayout);
}

void LoadTriangle()
{
    // create a triangle using the VERTEX struct
    Vertex OurVertices[] =
    {
    { 0.0f, 0.5f, 0.0f, { 1.0f, 0.0f, 0.0f, 1.0f } },
    { 0.45f, -0.5, 0.0f, { 0.0f, 1.0f, 0.0f, 1.0f } },
    { -0.45f, -0.5f, 0.0f, { 0.0f, 0.0f, 1.0f, 1.0f } }
    };

    // create the vertex buffer
    D3D11_BUFFER_DESC bd;
    ZeroMemory(&bd, sizeof(bd));
    bd.Usage = D3D11_USAGE_DYNAMIC;                // write access access by CPU and GPU
    bd.ByteWidth = sizeof(Vertex)* 3;             // size is the VERTEX struct * 3
    bd.BindFlags = D3D11_BIND_VERTEX_BUFFER;       // use as a vertex buffer
    bd.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;    // allow CPU to write in buffer
    device->CreateBuffer(&bd, NULL, &vertexBuffer);       // create the buffer

    // copy the vertices into the buffer
    D3D11_MAPPED_SUBRESOURCE ms;
    deviceContext->Map(vertexBuffer, NULL, D3D11_MAP_WRITE_DISCARD, NULL, &ms);    // map the buffer
    memcpy(ms.pData, OurVertices, sizeof(OurVertices));                 // copy the data
    deviceContext->Unmap(vertexBuffer, NULL);                                      // unmap the buffer
}

着色器文件(shaders.shader):

struct VOut
{
    float4 position : SV_POSITION;
    float4 color : COLOR;
};
VOut VShader(float4 position : POSITION, float4 color : COLOR)
{
    VOut output;
    output.position = position;
    output.color = color;
    return output;
}
float4 PShader(float4 position : SV_POSITION, float4 color : COLOR) : SV_TARGET
{
    return color;
}

如果在第119行取消DwmExtendFrameIntoClientArea调用的注释，那么它就得到了我正在寻找的效果。我想知道是否有一种方法可以在不使用dwm的情况下获得相同的效果(原因我不会进入)。

任何想法?

编辑:添加了工作示例的完整源代码。发现如果我调用DwmExtendFrameIntoClientArea，那么我得到了我想要的效果。但是我仍然想知道如果不使用dwm api是否有可能做到这一点。