OPENCV desktop capture Part II - c++

Question

Continuing in previous post from here OPENCV Destop Capture and this hwnd2mat function, a method to capture desktop as source in opencv is create a bitmap from the screen image with this hwnd2mat function. done.
this function is already create a bitmap from the screen image.but it gives weird effect like a trailing inside the video, i just want a normal video source more likely like this one . i've already try to find what cause it, but i don't know anymore.
#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include <Windows.h>
#include <iostream>
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 / 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;
}
int main(int argc, char **argv)
{
HWND hwndDesktop = GetDesktopWindow();
namedWindow("output", CV_WINDOW_NORMAL);
int key = 0;
while (key != 30 )
{
Mat src = hwnd2mat(hwndDesktop);
// you can do some image processing here
imshow("output", src);
key = waitKey(30); // you can change wait time
}
ReleaseCapture();
destroyAllWindows();
return 0;
}

Answer 1

Using GetDesktopWindow() will make infinite-mirror-effect, instead that, using what window you want capture, and me, i'm using FindWindowEx(), and use Spy++ to find what window you want to capture, that should works. but of course it will go to the next bug :).