// gcc -o em em.c -L/usr/X11R6/lib -I/usr/X11R6/include -lX11

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <X11/X.h>
#include <X11/Xlib.h>

#define MAX	(20)

const double c=0.3;
const double d=0.92;

int main (int argc, char *argv [])
{
double vx,vy;
int ox,oy;
int dw, dh;
Display *dpy;
Window rootwindow;
   
dpy = XOpenDisplay (NULL);
	if(!dpy) return 1;
rootwindow = DefaultRootWindow (dpy);
dw = DisplayWidth (dpy, DefaultScreen (dpy));
dh = DisplayHeight (dpy, DefaultScreen (dpy));

ox=-1;
vx=vy=0;

  	for(;;){
	int x, y, dummy;
	Window w=rootwindow;
	XQueryPointer (dpy, w,  &w, &w, &x, &y, &dummy, &dummy, &dummy);
		if(ox>=0){
		vx=(vx+((double)(x-ox))*c)*d;
		vy=(vy+((double)(y-oy))*c)*d;
	
			if(vx>MAX) vx=MAX;
			if(vx<-MAX) vx=-MAX;
			
			if(vy>MAX) vy=MAX;
			if(vy<-MAX) vy=-MAX;

			if(x+vx<0 || x+vx>=dw) vx*=-1;
			if(y+vy<0 || y+vy>=dh) vy*=-1;
		
		XWarpPointer (dpy, rootwindow, 0, 0, 0, 0, 0, (int)vx, (int)vy);
		}
	ox=x+(int)vx; oy=y+(int)vy;
	usleep(10000);
	}
    
XCloseDisplay (dpy);
}