#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <X11/Xlib.h>
#include <X11/extensions/shape.h>
#include <X11/Xutil.h>

int scr_width, scr_height;

uint64_t x, y, width, height;
Window window;

#define MIN_WIDTH 10
#define MIN_HEIGHT 10
#define MAX_WIDTH (800 - MIN_WIDTH)
#define MAX_HEIGHT (800 - MIN_HEIGHT)

static uint32_t
reflect (uint64_t i, uint64_t size)
{
    i = i % (size * 2);
    if (i >= size)
	i = size * 2 - i - 1;

    return i;
}

#define OUTLINE_WIDTH 3

void
set_shape (Display *dpy, Window window, XRectangle *rect)
{
    if (rect->width > OUTLINE_WIDTH * 2 &&
	rect->height > OUTLINE_WIDTH * 2)
    {
	XRectangle xrect;
	Region inner_xregion;
	Region outer_xregion;

	inner_xregion = XCreateRegion ();
	outer_xregion = XCreateRegion ();

	xrect.x = 0;
	xrect.y = 0;
	xrect.width = rect->width;
	xrect.height = rect->height;

	XUnionRectWithRegion (&xrect, outer_xregion, outer_xregion);

	xrect.x += OUTLINE_WIDTH;
	xrect.y += OUTLINE_WIDTH;
	xrect.width -= OUTLINE_WIDTH * 2;
	xrect.height -= OUTLINE_WIDTH * 2;

	XUnionRectWithRegion (&xrect, inner_xregion, inner_xregion);

	XSubtractRegion (outer_xregion, inner_xregion, outer_xregion);

	XShapeCombineRegion (dpy, window,
			     ShapeBounding, 0, 0, outer_xregion, ShapeSet);

	XDestroyRegion (outer_xregion);
	XDestroyRegion (inner_xregion);
    }
}

static void
update_window (Display *dpy)
{
    uint32_t real_x, real_y, real_width, real_height;
    XRectangle rect;

    real_width = reflect (width, MAX_WIDTH) + MIN_WIDTH;
    real_height = reflect (height, MAX_HEIGHT) + MIN_HEIGHT;

    real_x = reflect (x, scr_width);
    real_y = reflect (y, scr_height);

    if (real_x + real_width >= scr_width)
	real_x = scr_width - real_width;
    if (real_y + real_height >= scr_height)
	real_y = scr_height - real_height;

    XMoveResizeWindow (dpy, window, real_x, real_y,
		       real_width, real_height);

    rect.x = real_x;
    rect.y = real_y;
    rect.width = real_width;
    rect.height = real_height;

    set_shape (dpy, window, &rect);
    
    
    x += rand () % 20;
    width += rand () % 20;
    y += rand () % 20;
    height += rand () % 20;

    XSync (dpy, False);
}

int
main ()
{
    Display *dpy = XOpenDisplay (NULL);
    XSetWindowAttributes attr;

    attr.override_redirect = True;
    attr.background_pixel = 0;

    x = 10;
    y = 10;
    width = 400;
    height = 400;

    scr_width = DisplayWidth (dpy, 0);
    scr_height = DisplayHeight (dpy, 0);

    window = XCreateWindow (
	dpy, DefaultRootWindow (dpy), x, y, width, height,
	0, 0,
	InputOutput, DefaultVisual (dpy, 0),
	CWOverrideRedirect | CWBackPixel, &attr);

    XMapWindow (dpy, window);

    while (1)
    {
	update_window (dpy);

	usleep (10000);
    }

    XSync (dpy, False);

    sleep (10);
}