仅截图窗口的特定区域

Question

I'm currently screenshotting windows using the following lines of code:

UpdateWindow(hwnd);
HDC window_dc = GetDC(hwnd);
HDC res = CreateCompatibleDC(window_dc);
RECT r;
GetClientRect(hwnd, &r);
HBITMAP bmp = CreateCompatibleBitmap(window_dc, r.right - r.left, r.bottom - r.top);
SelectObject(res, bmp);
PrintWindow(hwnd, res, PW_CLIENTONLY);
DeleteObject(bmp);
ReleaseDC(hwnd, window_dc);

Now is there a way, to only screenshot a specific area of my HWND? I realized, that on some applications, the screenshotting takes siginificantly longer when the window is only a little bit larger. So I figured if I was able to only screenshot the important frame, I could really improve my speed.

EDIT: It needs to work for windows which are in the background, eg. overlapped by other windows.

Answer 1

You could try it like this:

bool ScreenShot(HWND hwnd, int x, int y, int w, int h, LPCSTR file){
    HDC source = GetDC(hwnd);
    HDC memory = CreateCompatibleDC(source);

    HBITMAP bitmap = CreateCompatibleBitmap(source, w, h);
    HBITMAP bitmapOld = (HBITMAP)SelectObject(memory, hBitmap);

    BitBlt(memory, 0, 0, w, h, source, x, y, SRCCOPY);
    hBitmap = (HBITMAP)SelectObject(memory, bitmapOld);

    DeleteDC(source);
    DeleteDC(memory);

    HPALETTE pal = NULL;
    if(saveBitmap(file, bitmap, pal)) return true;
    return false;
}