我在主窗口上有几个子窗口，有的是GDI窗口，有的是opengl渲染的窗口，一个功能是用rect截取图像(可能覆盖不同的窗口组合)。此功能在 windows xp 下工作正常。但是在windows 7下，所有opengl渲染的窗口都是黑色的。我做了一些研究，有人说 gdi 不能通过窗口 DC 直接访问帧缓冲区，必须使用 glReadPixels 来组合位图。然而，这种方法很尴尬，因为我必须分别组合该矩形中的每个窗口。谁有更好的选择？

这是我捕获 bmp 的代码:

   void MainWndClass::catchBmp(const char* path_fn, bool drawAreaOnly /*=0*/) 
{   
    CDC *pDC=GetDC();

    int BitPerPixel = pDC->GetDeviceCaps(BITSPIXEL);
    int Left,Top,Width,Height;

    if (drawAreaOnly)
    {
        Left = rBDWin.left;
        Top = rBDWin.top;
        Width = rBDWin.right-rBDWin.left;
        Width = Width/4*4;
        Height = rBDWin.bottom-rBDWin.top;
        Height = Height/4*4;
    }
    else
    {
        Left=rbmpWin.left;
        Top=rbmpWin.top;
        Width=rbmpWin.right-rbmpWin.left;
        Width=Width/4*4;
        Height=rbmpWin.bottom-rbmpWin.top;
        Height=Height/4*4;
    }   

    CDC memDC;
    memDC.CreateCompatibleDC(pDC);



    CBitmap memBitmap, *oldmemBitmap;
    memBitmap.CreateCompatibleBitmap(pDC, Width, Height);
    //it seems does no work
    //short bpp=24;
    if(BitPerPixel>24) BitPerPixel=24;
    memBitmap.SetBitmapBits(2,&BitPerPixel);

    oldmemBitmap = memDC.SelectObject(&memBitmap);
    //copy the bitmap from the pDC (source)
    memDC.BitBlt(0, 0, Width, Height, pDC, Left, Top, SRCCOPY);
    /*
    CString title;
    GetWindowText(title);

      memDC.SetBkMode(TRANSPARENT);
      memDC.TextOut(64,4,title);
    */
    BITMAP bmp;
    memBitmap.GetBitmap(&bmp);
    if(bmp.bmBitsPixel>24) 
    {
        bmp.bmBitsPixel=24;
        //bmp.bmWidthBytes=bmp.bmWidth*3;
    }

    bmp.bmWidthBytes=bmp.bmWidth*(bmp.bmBitsPixel/8);

    FILE *fp=NULL;

    //path_fn+=".bmp";
    fp=fopen((LPCTSTR)path_fn,"w+b");

    BITMAPINFOHEADER bih = {0};
    bih.biBitCount = bmp.bmBitsPixel;
    bih.biCompression = BI_RGB;
    bih.biHeight = bmp.bmHeight;
    bih.biPlanes = 1;
    bih.biSize = sizeof(BITMAPINFOHEADER);
    bih.biSizeImage = bmp.bmWidthBytes * bmp.bmHeight;
    bih.biWidth = bmp.bmWidth;

    BITMAPFILEHEADER bfh = {0};
    bfh.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
    bfh.bfSize = bfh.bfOffBits + bmp.bmWidthBytes * bmp.bmHeight;
    bfh.bfType = (WORD)0x4d42;

    if(fp)
    {
        fwrite(&bfh, 1, sizeof(BITMAPFILEHEADER), fp);

        fwrite(&bih, 1, sizeof(BITMAPINFOHEADER), fp);
    }

    byte * p = new byte[bmp.bmWidthBytes * bmp.bmHeight];
    //copy the bits to the buffer
    int ret=GetDIBits(memDC.m_hDC, (HBITMAP) memBitmap.m_hObject, 0, Height, p, 
        (LPBITMAPINFO) &bih, DIB_RGB_COLORS);

    if(fp)
        fwrite(p, 1, bmp.bmWidthBytes * bmp.bmHeight, fp);

    delete [] p;

    if(fp)
        fclose(fp);


    memDC.SelectObject(oldmemBitmap);
}

opengl窗口配置为:

PIXELFORMATDESCRIPTOR pixelDesc =
{
    sizeof(PIXELFORMATDESCRIPTOR),
        1,
        PFD_DRAW_TO_WINDOW|PFD_SUPPORT_OPENGL|
        PFD_DOUBLEBUFFER,
        PFD_TYPE_RGBA,
        24,
        0,0,0,0,0,0,
        0,
        0,
        0,
        0,0,0,0,
        32,//
        0,
        0,
        PFD_MAIN_PLANE,
        0,
        0,0,0
};  

我想再强调一下这个事实: xp下可以，win7下不行(opengl窗口部分是黑色的)

最佳答案

你好，我终于找到了一个完美的解决方案。根据 Mats Pertersson 提供的信息，我很确定这就是原因，因为它符合事实。 Windows 7引入了透明窗口外观，每个窗口都不是最终效果。最终结果(屏幕输出)由所有窗口组成。所以我找到了解决方案，捕获最终屏幕而不是捕获主窗口。并且它在 xp 和 win 7 下都完美运行。

主要变化:所有DC来自屏幕而不是窗口，因此相关函数全部更改为全局gdi函数。

代码如下:

    catchBmp(const char* path_fn, bool drawAreaOnly /*=0*/) 
{   
    //CDC *pDC=GetDC();
    HDC hdcScreen;

    HDC hdcMemDC = NULL;
    HBITMAP hbmScreen = NULL;
    BITMAP bmpScreen;

    hdcScreen=::GetDC(NULL);


    int BitPerPixel = ::GetDeviceCaps(hdcScreen,BITSPIXEL);
    int Left,Top,Width,Height;

    if (drawAreaOnly)
    {
        Left = rBDWin.left;
        Top = rBDWin.top;
        Width = rBDWin.right-rBDWin.left;
        Width = Width/4*4;
        Height = rBDWin.bottom-rBDWin.top;
        Height = Height/4*4;
    }
    else
    {
        Left=rbmpWin.left;
        Top=rbmpWin.top;
        Width=rbmpWin.right-rbmpWin.left;
        Width=Width/4*4;
        Height=rbmpWin.bottom-rbmpWin.top;
        Height=Height/4*4;
    }   

    hdcMemDC=::CreateCompatibleDC(hdcScreen);

    hbmScreen=::CreateCompatibleBitmap(hdcScreen,Width,Height);


    if(BitPerPixel>24) BitPerPixel=24;

    ::SetBitmapBits(hbmScreen,2,&BitPerPixel);
    ::SelectObject(hdcMemDC,hbmScreen);

    BitBlt(hdcMemDC, 
        0,0,Width,Height,hdcScreen,Left,Top,SRCCOPY);

    ::GetObject(hbmScreen,sizeof(BITMAP),&bmpScreen);
    if(bmpScreen.bmBitsPixel>24) 
    {
        bmpScreen.bmBitsPixel=24;
    }

    bmpScreen.bmWidthBytes=bmpScreen.bmWidth*(bmpScreen.bmBitsPixel/8);

    FILE *fp=NULL;

    fp=fopen((LPCTSTR)path_fn,"w+b");

    BITMAPINFOHEADER bih = {0};
    bih.biBitCount = bmpScreen.bmBitsPixel;
    bih.biCompression = BI_RGB;
    bih.biHeight = bmpScreen.bmHeight;
    bih.biPlanes = 1;
    bih.biSize = sizeof(BITMAPINFOHEADER);
    bih.biSizeImage = bmpScreen.bmWidthBytes * bmpScreen.bmHeight;
    bih.biWidth = bmpScreen.bmWidth;

    BITMAPFILEHEADER bfh = {0};
    bfh.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
    bfh.bfSize = bfh.bfOffBits + bmpScreen.bmWidthBytes * bmpScreen.bmHeight;
    bfh.bfType = (WORD)0x4d42;

    if(fp)
    {
        fwrite(&bfh, 1, sizeof(BITMAPFILEHEADER), fp);

        fwrite(&bih, 1, sizeof(BITMAPINFOHEADER), fp);
    }

    byte * p = new byte[bmpScreen.bmWidthBytes * bmpScreen.bmHeight];

    GetDIBits(hdcScreen, hbmScreen, 0, Height, p, (LPBITMAPINFO) &bih, DIB_RGB_COLORS);
    if(fp)
        fwrite(p, 1, bmpScreen.bmWidthBytes * bmpScreen.bmHeight, fp);

    delete [] p;

    if(fp)
        fclose(fp);

    ::DeleteObject(hbmScreen);
    ::DeleteObject(hdcMemDC);
    ::ReleaseDC(NULL,hdcScreen);

    //memDC.SelectObject(oldmemBitmap);
}

关于c++ - 在 win7 下，为 opengl 窗口捕获的图像是黑色的，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28285601/