[SOLVED] Grabbing window content

El Mago · 04-09-2010, 08:25 AM

I'd like to write a C/C++ program, that would grab content of window (in form of pixmap), which belongs to another application and do something with it. However, I ran into problems already at the beginning. In all toolkits I have searched through, I only found one function that claims to do what I want, namely XGetImage from Xlib. However, among other parameters like Display, coordinates, etc., it requires a Drawable. How do I specify a Drawable, that would correspond to the window I want to grab content of?
Or even better question: is there any easier way to achieve this?

paulsm4 · 04-10-2010, 08:10 PM

Suggestion - don't reinvent the wheel. Just use one of the standard screenshot programs available to you (all of which can easily be called from C/C++):

http://tips.webdesign10.com/how-to-t...n-ubuntu-linux
http://www.sb.fsu.edu/~xray/Manuals/ScreenCapture.html

Otherwise, download the source for one of the above programs (the one you like the best) and simply look at how they do it.

'Hope that helps .. PSM

El Mago · 04-15-2010, 10:26 AM

Thanks for the links, they were useful. I managed to came up with the following solution, it waits for 2 seconds in order to get focus into window of interest and it updates the window content each second:

Code:

#include <Xlib.h>
#include <stdio.h>


int main(int argc, char **argv)
{ Display *dp;
  XImage *im;
  Window win, fw, root;
  GC gc;
  int ok, x, y;
  unsigned int w, h, bw, d;

  dp = XOpenDisplay(0);
  
  win = XCreateSimpleWindow(dp, RootWindow(dp, 0), 0, 0, 900, 700, 2, BlackPixel(dp, 0), WhitePixel(dp, 0));
  
  gc = XCreateGC(dp, win, 0, 0);
  
  XSelectInput(dp, win, StructureNotifyMask);

  XMapWindow(dp, win);
  
  for(;;) {
	    XEvent e;
	    XNextEvent(dp, &e);
	    if (e.type == MapNotify)
		  break;
      }

  sleep(2);
  XGetInputFocus(dp, &fw, &ok);
  
  XGetGeometry(dp, fw, &root, &x, &y, &w, &h, &bw, &d);
  
  while (1)
  { im = XGetImage(dp, fw, 0, 0, w, h, AllPlanes, ZPixmap);
    
    XPutImage(dp, win, gc, im, 0, 0, 0, 0, w, h);
    
    XFlush(dp);
    
    
    sleep(1);
    }
  
  XDestroyWindow(dp, w);
  XCloseDisplay(dp);
  }