Path: utzoo!attcan!uunet!jarthur!usc!snorkelwacker!bloom-beacon!HARVARD.HARVARD.EDU!jimf%saber
From: jimf%saber@HARVARD.HARVARD.EDU
Newsgroups: comp.windows.x
Subject: Re: Help on Invisible windows
Message-ID: <9003211620.AA16247@armory>
Date: 21 Mar 90 16:20:27 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 70

|     How do I create the "invisible (shadow/outline) windows" that 
|"twm" uses when a user moves his window (so that the user knows where
|the destination is going to be)?

The simplest way is something like:

-- cut here --
get_window_location(disp, width, height, rx, ry)
     int *rx, *ry;      /* return location */
     int width, height; /* width and height to outline */
{
    int       x, y;
    Display  *disp;
    Window    root;
    long      junk;
    XGCValues gcv;
    GC        gc;
    union {
	XEvent       generic;
	XAnyEvent    any;
	XButtonEvent button;
	XMotionEvent pointer;
    } xevent;

    scrn= DefaultScreen(disp);
    root= RootWindow(disp, scrn);
    XQueryPointer(disp, root, &junk, &junk, &x, &y, &junk, &junk, &junk);
    gcv.function= GXxor;
    gcv.foreground= 1;
    gcv.subwindow_mode= IncludeInferiors;
    gc= XCreateGC(disp, root,
		  GCFunction | GCForeground | GCSubwindowMode, &gcv);

    /* get mean */
    XGrabPointer(disp, root, False, ButtonPressMask | PointerMotionMask,
		 GrabModeSync, GrabModeSync, None, None, CurrentTime);

    /* zorch the root window */
    XDrawRectangle(disp, root, gc, x, y, width, height);
    for (;;) {
	XNextEvent(disp, &xevent);
	switch(xevent.any.type) {
	case ButtonPress:
	    goto done; /* nasty */
	case MotionNotify:
	    XDrawRectangle(disp, root, gc, x, y, width, height);
	    x= xevent.pointer.x;
	    y= xevent.pointer.y;
	    XDrawRectangle(disp, root, gc, x, y, width, height);
	}
    }
 done:
    /* unzorch the root window */
    XDrawRectangle(disp, root, gc, x, y, width, height);
    XUngrabPointer(disp, CurrentTime); /* sigh of relief */
    XFreeGC(disp, gc);
    *rx= x;
    *ry= y;
}
-- cut here --

That's quick and dirty but it works pretty well.  You can get a lot
more sophisticated (especially if you're using color) and you should
probably consider error checking the XGrabPointer call.

Happy hacking,

jim frost
saber software
jimf@saber.com