#include <stdio.h>
#include <X11/Xos.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>

int main() {
    Display *dpy;
    int scr;
    Window win;
    XSetWindowAttributes xswa;
    char *xservname=NULL;

    if ((dpy=XOpenDisplay(xservname)) == NULL) {
	fprintf(stderr,"can not open %s\n",XDisplayName(xservname));
	exit(-1);
    }
    scr = DefaultScreen(dpy);
    xswa.background_pixel = WhitePixel(dpy,scr);
    xswa.border_pixel = BlackPixel(dpy,scr);
    xswa.event_mask = ExposureMask;
    win = XCreateWindow(dpy,RootWindow(dpy,scr),0,0,320,240,1,
			CopyFromParent,CopyFromParent,CopyFromParent,
			CWBackPixel | CWBorderPixel | CWEventMask, &xswa);
    XMapWindow(dpy,win);
    for (;;) {
	XEvent ev;
	XNextEvent(dpy,&ev);
	switch (ev.type) {
	  case Expose:
	    XClearWindow(dpy,win);
	    break;
	  default:
	    printf("unknown event %d\n",ev.type);
	    break;
	}
    }
}