Screen Capture

screenCapture.cpp

#include <iostream>
#include <Windows.h>
#include <opencv2/opencv.hpp>

using namespace std;
using namespace cv;

Mat captureScreenMat(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);
       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;
 }

int main()
{
    namedWindow("Screen Capture", CV_WINDOW_NORMAL);
    HWND hwnd = GetDesktopWindow();
    int key = 0;
    while(key != 27){
        Mat src = captureScreenMat(hwnd);
        key = waitKey(30);
    }

    return 0;
}