% from Symbolics?

rec = record[x1, y1, x2, y2: int]
ar = array[rec]

qixdemo = proc ()
    vsize = 100 * 2
    bwidth: int := int$parse(xdemo_default("qix", "BorderWidth"))
       except when not_found, overflow, bad_format: bwidth := 2 end
    back: x_pixmap := x_display$white()
    bdr: x_pixmap := x_display$black()
    plane: int := 1
    if x_display$cells() > 2
       then begin
	    r, g, b: int := x_parse_color(xdemo_default("qix", "Border"))
	    bdr := x_pixmap$tile(x_display$alloc_color(r, g, b))
	    end except when not_found: end
	    cback: string := xdemo_default("qix", "Background")
	       except when not_found: cback := "" end
	    cfore: string := xdemo_default("qix", "Foreground")
	       except when not_found: cfore := "" end
	    if string$empty(cback)  cand  string$empty(cfore)
	       then exit done end
	    pixs: pixellist
	    pixs, plane := x_display$alloc_cells(1, 1, false)
	    back := x_pixmap$tile(pixs[1])
	    r, g, b: int
	    if string$empty(cback)
	       then r, g, b := x_display$query_color(WhitePixel)
	       else r, g, b := x_parse_color(cback)
	       end
	    x_display$store_color(pixs[1], r, g, b)
	    if string$empty(cfore)
	       then r, g, b := x_display$query_color(BlackPixel)
	       else r, g, b := x_parse_color(cfore)
	       end
	    x_display$store_color(pixs[1] + plane, r, g, b)
       end except when done: end
    w: x_window, wid0, hgt0: int := x_cons("qix", back, bdr,
					   xdemo_geometry(), "=400x400+1+1",
					   40, 40, bwidth)
    w.name := "qix"
    w.input := UnmapWindow
    x_window$map(w)
    w.input := ExposeWindow + UnmapWindow
    vlist: x_vlist := x_vlist$create(vsize)
    ev: event := x_input$empty_event()
    while true do
	x_window$clear(w)
	sx, sy, width, height, bw, ms, wk: int, iw: x_window := x_window$query(w)
	if width <= 30  cor  height <= 30
	   then x_window$destroy(w)
		return
	   end
	hsize: int := 100 + random$next(int$min(width, height) / 8)
	h: ar := ar$fill_copy(0, hsize, rec${x1, y1, x2, y2: 0})
	i: int := 0
	idx: int := 1
	x1: int := 0
	y1: int := height - 1
	x2: int := 0
	y2: int := height - 1
	dx1: int := 5
	dy1: int := 12
	dx2: int := 12
	dy2: int := 5
	first: bool := true
	while ~x_input$pending() do
	    r: rec := h[i]
	    if ~first
	       then x_vlist$store(vlist, idx, r.x1, r.y1, VertexDontDraw)
		    idx := idx + 1
		    x_vlist$store(vlist, idx, r.x2, r.y2, VertexDrawLastPoint)
		    if idx = vsize
		       then x_window$draw(w, vlist, vsize, 0, 1, 1,
					  GXinvert, plane)
			    idx := 1
		       else idx := idx + 1
		       end
	       end
	    r.x1 := x1
	    r.y1 := y1
	    r.x2 := x2
	    r.y2 := y2
	    x_vlist$store(vlist, idx, x1, y1, VertexDontDraw)
	    idx := idx + 1
	    x_vlist$store(vlist, idx, x2, y2, VertexDrawLastPoint)
	    if idx = vsize
	       then x_window$draw(w, vlist, vsize, 0, 1, 1, GXinvert, plane)
		    idx := 1
	       else idx := idx + 1
	       end
	    i := i + 1
	    if i = hsize
	       then i := 0
		    first := false
	       end
	    dx1 := int$max(-12, int$min(dx1 + random$next(3) - 1, 12))
	    x1 := x1 + dx1
	    if x1 >= width  cor  x1 < 0
	       then x1 := x1 - 2 * dx1
		    dx1 := -dx1
	       end
	    dy1 := int$max(-12, int$min(dy1 + random$next(3) - 1, 12))
	    y1 := y1 + dy1
	    if y1 >= height  cor  y1 < 0
	       then y1 := y1 - 2 * dy1
		    dy1 := -dy1
	       end
	    dx2 := int$max(-12, int$min(dx2 + random$next(3) - 1, 12))
	    x2 := x2 + dx2
	    if x2 >= width  cor  x2 < 0
	       then x2 := x2 - 2 * dx2
		    dx2 := -dx2
	       end
	    dy2 := int$max(-12, int$min(dy2 + random$next(3) - 1, 12))
	    y2 := y2 + dy2
	    if y2 >= height  cor  y2 < 0
	       then y2 := y2 - 2 * dy2
		    dy2 := -dy2
	       end
	    end
	x_input$deq(ev)
	if ev.kind = UnmapWindow
	   then x_input$deq(ev) end
	end
    end qixdemo