Hwnd2mat function unidentified

i just installed OpenCV and it works, but when i tried to use the hwnd2mat function it didn’t recognize it. This is my code:
#include <opencv2/opencv.hpp>
#include <Windows.h>

using namespace std;
using namespace cv;

int main()
HWND num = GetDesktopWindow();
Mat src = hwnd2mat(num);

return 0;


i didn’t find anything about this problem online so if someone knows how to solve it i would appreciate it

this is not an opencv function, but a piece of code, that someone wrote, and is now circulating on the net. just google it, please.

thanks, i didn’t realize that it’s a function written by someone, not one from OpenCV

anyway, found it on my disk:

// link gdi32 !
Mat hwnd2mat(HWND hwnd=GetDesktopWindow()){

    HDC hwindowDC,hwindowCompatibleDC;

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

    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/2;  //change this to whatever size you want to resize to
    width = windowsize.right/2;


    // 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);
    ReleaseDC(hwnd, hwindowDC);

    return src;

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