Question

之前我已经能够做到这一点，我不知道两周前和最后一次Windows更新之间发生了什么变化，但出于某种原因SetPixelFormat没有创建alpha通道。

gDebugger显示窗口的后台缓冲区只有3个通道。

白色+ 0 alpha呈现为白色。

因此，我正在做的事情本身存在一些错误，或者更新了它。

下面的代码应该可以粘贴到一个空的VS项目中。

#include <Windows.h>
#include <dwmapi.h>
#include <gl/GL.h>

#pragma comment(lib,"opengl32.lib")
#pragma comment(lib,"dwmapi.lib")

HWND hWnd = 0;
HDC hDC = 0;
HGLRC hRC = 0;
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);

int APIENTRY WinMain(
    HINSTANCE hInstance,
    HINSTANCE hPrevInstance,
    LPSTR lpCmdLine,
    int nCmdShow
    )
{   
    WNDCLASSEX wcex = {0};

    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.lpfnWndProc    = WndProc;
    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wcex.lpszClassName  = TEXT("why_class");

    RegisterClassEx(&wcex);
    // no errors

    hWnd = CreateWindowEx(
            NULL,
            TEXT("why_class"),
            TEXT("why_window"),
            WS_OVERLAPPEDWINDOW,
            128,128,
            256,256,
            NULL,
            NULL,
            hInstance,
            NULL
        );
    // no errors

    PIXELFORMATDESCRIPTOR pfd = {0};
    pfd.nSize = sizeof(pfd);
    pfd.nVersion = 1;
    pfd.dwFlags = PFD_DRAW_TO_WINDOW|
        PFD_SUPPORT_OPENGL|
        PFD_DOUBLEBUFFER|
        PFD_SUPPORT_COMPOSITION;
    pfd.cColorBits = 32;
    pfd.cAlphaBits = 8;     // need an alpha channel
    pfd.cDepthBits = 24;
    pfd.cStencilBits = 8;

    hDC = GetDC(hWnd);
    int i = ChoosePixelFormat(hDC,&pfd);
    SetPixelFormat(hDC,i,&pfd);
    // no errors

    hRC = wglCreateContext(hDC);
    // no errors

    wglMakeCurrent(hDC,hRC);
    // no errors

    // EDIT: Turn on alpha testing (which actually won't
    // fix the clear color problem below)
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);

    // EDIT: Regardless of whether or not GL_BLEND is enabled,
    // a clear color with an alpha of 0 should (or did at one time)
    // make this window transparent

    glClearColor(
        0,0,0,  // if this is (1,1,1), the window renders
                // solid white regardless of the alpha
        0   // changing the alpha here has some effect
        );

    DWM_BLURBEHIND bb = {0};
    bb.dwFlags = DWM_BB_ENABLE|DWM_BB_TRANSITIONONMAXIMIZED;
    bb.fEnable = TRUE;
    bb.fTransitionOnMaximized = TRUE;
    DwmEnableBlurBehindWindow(hWnd,&bb);
    // no errors

    ShowWindow(hWnd, SW_SHOWNORMAL);
    UpdateWindow(hWnd);
    // no errors

    MSG msg = {0};
    while(true){
        GetMessage(&msg,NULL,NULL,NULL);
        if(msg.message == WM_QUIT){
            return (int)msg.wParam;
        }
        TranslateMessage(&msg);
        DispatchMessage(&msg);

        glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

        glBegin(GL_TRIANGLES);
        // this vertex should be transparent,
        // as it was when I last built this test
        //
        // it renders as white
        glColor4f(1,1,1,0);
        glVertex2f(0,0);
        glColor4f(0,1,1,1);
        glVertex2f(1,0);
        glColor4f(1,0,1,1);
        glVertex2f(0,1);
        glEnd();

        SwapBuffers(hDC);
    }

    return (int)msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{   
    switch (message)
    {
    case WM_DESTROY:
        {
            PostQuitMessage(0);
        }return 0;
    default:
        break;
    }

    return DefWindowProc(hWnd, message, wParam, lParam);
}

Answer 1

您通常无法获得具有32位颜色和8位alpha的帧缓冲区。

我没有尝试过您的代码，但建议将颜色位切换为24。

pfd.cColorBits = 24;
pfd.cAlphaBits = 8;

Answer 2

如果您想使用混合，只需致电：

glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

虽然为了实现这一点，你必须在三角形后面加上一些东西才能融合（黑色背景不算数！）

SetPixelFormat没有为OpenGL创建alpha通道

2 个答案: