How to capture the desktop in OpenCV (ie. turn a bitmap into a Mat)?

Question

I want to use OpenCV to process my desktop as if it were a video stream.
I am familiar with OpenCV.
I am not familiar with the Windows API. I realize there are other ways to capture the screen, but for the purposes of my question, I need it to be done using OpenCV.

Here is my (super naive) code:

HWND hDesktopWnd; HDC hDesktopDC; hDesktopWnd=GetDesktopWindow(); hDesktopDC=GetDC(hDesktopWnd);  // get the height and width of the screen int height = GetSystemMetrics(SM_CYVIRTUALSCREEN); int width = GetSystemMetrics(SM_CXVIRTUALSCREEN);  // create a bitmap HBITMAP hbDesktop = CreateCompatibleBitmap( hDesktopDC, width, height);  Mat src(height,width,CV_8UC4); src.data = (uchar*)hbDesktop;  imshow("output",src);  //fails :( 

There are similar questions on StackOverflow, but they are either for the old-style OpenCV, or for Android operating system.
I'm on windows 7 64x
Opencv 2.4.3

Thanks anyone who can answer this question.

Answer 1

After MUCH trial and error, I managed to write a function to do it. here it is for anyone else who might want it:

#include "stdafx.h" #include "opencv2/core/core.hpp" #include "opencv2/imgproc/imgproc.hpp" #include <opencv2/highgui/highgui.hpp> #include <Windows.h> #include <iostream> #include <string> using namespace std; using namespace cv;  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/2;  //change this to whatever size you want to resize to     width = windowsize.right/2;      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; }