How to get a screen image into a memory buffer?

Question

I\'ve been searching for a pure WIN32 way of getting the image data of a screen into a buffer, for analysis of the objects in the image later... Sadly I haven\'t found any.

Answer 1

There are multiple ways (you could use DirectX), but probably the simplest and easiest is to use GDI.

    // GetDC(0) will return screen device context
    HDC hScreenDC = GetDC(0);
    // Create compatible device context which will store the copied image
    HDC hMyDC= CreateCompatibleDC(hScreenDC );

    // Get screen properties
    int iScreenWidth = GetSystemMetrics(SM_CXSCREEN);
    int iScreenHeight = GetSystemMetrics(SM_CYSCREEN);
    int iBpi= GetDeviceCaps(hScreenDC ,BITSPIXEL);

    // Fill BITMAPINFO struct
    BITMAPINFO info;
    info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    info.bmiHeader.biWidth = iScreenWidth;
    info.bmiHeader.biHeight = iScreenHeight ;
    info.bmiHeader.biPlanes = 1;
    info.bmiHeader.biBitCount  = iBpi;
    info.bmiHeader.biCompression = BI_RGB;

    // Create bitmap, getting pointer to raw data (this is the important part)
    void *data;
    hBitmap = CreateDIBSection(hMyDC,&info,DIB_RGB_COLORS,(void**)&data,0,0);
    // Select it into your DC
    SelectObject(hMyDC,hBitmap);

    // Copy image from screen
    BitBlt(hMyDC, 0, 0, iScreenWidth, iScreenHeight, hScreenDC , 0, 0, SRCCOPY);

    // Remember to eventually free resources, etc.

It's been a while since I did this so I may be forgetting something, but that's the gist of it. A word of warning: this is NOT fast; when the screen is moving a lot, it may take 50ms or more to capture one frame. It's basically doing the equivalent of pressing the PrintScreen key.