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Good afternoon. I am trying to modify the function so that it wastes gpu and not cpu. Here is its initial view.

Mat hwnd2mat(HWND hwnd)
{
HDC hwindowDC, hwindowCompatibleDC;

int height, width, srcheight, srcwidth;
HBITMAP hbwindow;
Mat src;
BITMAPINFOHEADER  bi;

hwindowDC = GetDC(hwnd);
hwindowCompatibleDC = CreateCompatibleDC(hwindowDC);
SetStretchBltMode(hwindowCompatibleDC, COLORONCOLOR);

RECT windowsize;    // get the height and width of the screen
GetClientRect(hwnd, &windowsize);

srcheight = windowsize.bottom;
srcwidth = windowsize.right;
height = windowsize.bottom / 1;  //change this to whatever size you want to resize to
width = windowsize.right / 1;

src.create(height, width, CV_8UC4);

// create a bitmap
hbwindow = CreateCompatibleBitmap(hwindowDC, width, height);
bi.biSize = sizeof(BITMAPINFOHEADER);    //http://msdn.microsoft.com/en-us/library/windows/window/dd183402%28v=vs.85%29.aspx
bi.biWidth = width;
bi.biHeight = -height;  //this is the line that makes it draw upside down or not
bi.biPlanes = 1;
bi.biBitCount = 32;
bi.biCompression = BI_RGB;
bi.biSizeImage = 0;
bi.biXPelsPerMeter = 0;
bi.biYPelsPerMeter = 0;
bi.biClrUsed = 0;
bi.biClrImportant = 0;

// use the previously created device context with the bitmap
SelectObject(hwindowCompatibleDC, hbwindow);
// copy from the window device context to the bitmap device context
StretchBlt(hwindowCompatibleDC, 0, 0, width, height, hwindowDC, 0, 0, srcwidth, srcheight, SRCCOPY); //change SRCCOPY to NOTSRCCOPY for wacky colors !
GetDIBits(hwindowCompatibleDC, hbwindow, 0, height, src.data, (BITMAPINFO*)&bi, DIB_RGB_COLORS);  //copy from hwindowCompatibleDC to hbwindow

// avoid memory leak
DeleteObject(hbwindow);
DeleteDC(hwindowCompatibleDC);
ReleaseDC(hwnd, hwindowDC);

return src;
}

Here's how I change it, but nothing works for me. So that you do not look for a long time what exactly I am to change, then I will write. I changed

Mat src = UMat src
src.create (height, width, CV_8UC4) = src.create (height, width, CV_8UC4, USAGE_ALLOCATE_DEVICE_MEMORY);
GetDIBits (hwindowCompatibleDC, hbwindow, 0, height, src.data, (BITMAPINFO *) & bi, DIB_RGB_COLORS) = GetDIBits (hwindowCompatibleDC, hbwindow, 0, height, src.u-> data, (BITMAPINFO_R *); & bi_DIBOLORS

All Code:

UMat hwnd2mat(HWND hwnd)
{
HDC hwindowDC, hwindowCompatibleDC;

int height, width, srcheight, srcwidth;
HBITMAP hbwindow;
UMat src;
BITMAPINFOHEADER  bi;

hwindowDC = GetDC(hwnd);
hwindowCompatibleDC = CreateCompatibleDC(hwindowDC);
SetStretchBltMode(hwindowCompatibleDC, COLORONCOLOR);

RECT windowsize;    // get the height and width of the screen
GetClientRect(hwnd, &windowsize);

srcheight = windowsize.bottom;
srcwidth = windowsize.right;
height = windowsize.bottom / 1;  //change this to whatever size you want to resize to
width = windowsize.right / 1;

src.create(height, width, CV_8UC4, USAGE_ALLOCATE_DEVICE_MEMORY);

// create a bitmap
hbwindow = CreateCompatibleBitmap(hwindowDC, width, height);
bi.biSize = sizeof(BITMAPINFOHEADER);    //http://msdn.microsoft.com/en-us/library/windows/window/dd183402%28v=vs.85%29.aspx
bi.biWidth = width;
bi.biHeight = -height;  //this is the line that makes it draw upside down or not
bi.biPlanes = 1;
bi.biBitCount = 32;
bi.biCompression = BI_RGB;
bi.biSizeImage = 0;
bi.biXPelsPerMeter = 0;
bi.biYPelsPerMeter = 0;
bi.biClrUsed = 0;
bi.biClrImportant = 0;

// use the previously created device context with the bitmap
SelectObject(hwindowCompatibleDC, hbwindow);
// copy from the window device context to the bitmap device context
StretchBlt(hwindowCompatibleDC, 0, 0, width, height, hwindowDC, 0, 0, srcwidth, srcheight, SRCCOPY); //change SRCCOPY to NOTSRCCOPY for wacky colors !
GetDIBits(hwindowCompatibleDC, hbwindow, 0, height, src.u->data, (BITMAPINFO*)&bi, DIB_RGB_COLORS);  //copy from hwindowCompatibleDC to hbwindow

// avoid memory leak
DeleteObject(hbwindow);
DeleteDC(hwindowCompatibleDC);
ReleaseDC(hwnd, hwindowDC);

return src;
}