i tried to run this code on a game and it doesn t work(it gets a black screen as ouput)
the only app that worked partially was the File Explorer -Home Window or Gallery Window,but the image is not positioned well in the output,and it doesn t show the entire window(the output is partially black)
This is the code i’ve been using:

cv::Mat getMat(HWND wnd) {

    HDC deviceContext = GetDC(wnd);
    HDC memoryDeviceContext = CreateCompatibleDC(deviceContext);

    RECT windowRect;
    GetClientRect(wnd, &windowRect);

    int height = windowRect.bottom;
    int width = windowRect.right;

    HBITMAP bitmap = CreateCompatibleBitmap(deviceContext, width, height);

    SelectObject(memoryDeviceContext, bitmap);

    //copy
    BitBlt(memoryDeviceContext, 0, 0, width, height, deviceContext, 0, 0, SRCCOPY);


    //specify format by using bitmapinfoheader
    BITMAPINFOHEADER bi;
    bi.biSize = sizeof(BITMAPINFOHEADER);
    bi.biWidth = width;
    bi.biHeight = -height;
    bi.biPlanes = 1;
    bi.biBitCount = 32;
    bi.biCompression = BI_RGB;
    bi.biSizeImage = 1; 
    

    cv::Mat mat = cv::Mat(height, width, CV_8UC4); //8 biti int+4canale;

    //transform datele si le pun in mat
    GetDIBits(memoryDeviceContext, bitmap, 0, height, mat.data, (BITMAPINFO*)&bi, DIB_RGB_COLORS);

    //curat;
    DeleteObject(bitmap);
    DeleteDC(memoryDeviceContext); 
    ReleaseDC(wnd, deviceContext);

    return mat;
}