rgbdemo = proc ()
    basevalue = 2**8
    initialvalue = basevalue * 2**7
    offvalue = 2**16
    maxvalue = offvalue - basevalue
    pixs: pixellist, mask: int := x_display$alloc_cells(4, 0, false)
    defs: colordeflist := colordeflist$[colordef${pixel: pixs[1],
						  red: initialvalue,
						  green: 0,
						  blue: 0},
					colordef${pixel: pixs[2],
						  red: 0,
						  green: initialvalue,
						  blue: 0},
					colordef${pixel: pixs[3],
						  red: 0,
						  green: 0,
						  blue: initialvalue},
					colordef${pixel: pixs[4],
						  red: initialvalue,
						  green: initialvalue,
						  blue: initialvalue}]
    x_display$store_colors(defs)
    bwidth: int := int$parse(xdemo_default("rgb", "BorderWidth"))
       except when not_found, overflow, bad_format: bwidth := 2 end
    bdr: x_pixmap := x_display$black()
    mousep: int := BlackPixel
    begin
	r, g, b: int := x_parse_color(xdemo_default("rgb", "Border"))
	bdr := x_pixmap$tile(x_display$alloc_color(r, g, b))
	end except when not_found: end
    begin
	r, g, b: int := x_parse_color(xdemo_default("rgb", "Mouse"))
	mousep := x_display$alloc_color(r, g, b)
	end except when not_found: end
    w: x_window, wid0, hgt0: int := x_cons("rgb", x_pixmap$tile(pixs[4]), bdr,
					   xdemo_geometry(), "=200x200+1+1",
					   40, 40, bwidth)
    w.name := "rgb"
    x_window$map(w)
    sx, sy, width, height, wb, ms, wk: int, iw: x_window := x_window$query(w)
    w3: int := width / 3
    h3: int := height / 3
    rw: x_window := x_window$create(0, 0, w3, h3, x_pixmap$tile(pixs[1]), w,
				    0, x_pixmap$none())
    gw: x_window := x_window$create(w3, 0, w3, h3, x_pixmap$tile(pixs[2]), w,
				    0, x_pixmap$none())
    bw: x_window := x_window$create(2 * w3, 0, width - 2 * w3, h3,
				    x_pixmap$tile(pixs[3]), w,
				    0, x_pixmap$none())
    x_window$map_subwindows(w)
    cr: x_cursor := x_cursor$scons(cross_width, cross_height,
				   cross, cross_mask,
				   pixs[4], mousep, cross_x, cross_y,
				   GXcopy)
    w.cursor := cr
    w.input := ExposeWindow
    rw.input := ButtonPressed + ButtonReleased + MiddleDownMotion
    gw.input := ButtonPressed + ButtonReleased + MiddleDownMotion
    bw.input := ButtonPressed + ButtonReleased + MiddleDownMotion
    f: x_font := x_font$create("8x13")
    rgb: string := ""
    rgbx: int := (width - x_font$width(f, "ffffff")) / 2
    rgby: int := height - h3
    ev: event := x_input$empty_event()
    tracking: bool := false
    while true do
	if string$empty(rgb)
	   then rgb := string$rest(i_hunparse((defs[4].red + offvalue) / basevalue), 2) ||
		       string$rest(i_hunparse((defs[4].green + offvalue) / basevalue), 2) ||
		       string$rest(i_hunparse((defs[4].blue + offvalue) / basevalue), 2)
		x_window$text(w, rgb, f, WhitePixel, BlackPixel, rgbx, rgby)
	   end
	x_input$deq(ev)
	if ev.kind = ExposeWindow
	   then if ev.sub = x_window$none()
		   then sx, sy, width, height, wb, ms, wk, iw := x_window$query(w)
			if width <= 30  cor  height <= 30
			   then x_window$destroy(w)
				return
			   end
			w3 := width / 3
			h3 := height / 3
			x_window$change(rw, w3, h3)
			x_window$configure(gw, w3, 0, w3, h3)
			x_window$configure(bw, 2 * w3, 0, width - 2 * w3, h3)
			rgb := ""
			rgbx := (width - x_font$width(f, "ffffff")) / 2
			rgby := height - h3
		   end
		continue
	 elseif ev.kind = MouseMoved  cor  ev.value = MiddleButton
	   then y: int := ev.y
		if ev.kind = MouseMoved
		   then x: int
			sub: x_window
			x, y, sub := x_window$query_mouse(ev.win)
		   else tracking := ~tracking
		   end
		if y < 0
		   then y := 0
		 elseif y >= h3
		   then y := h3 - 1 end
		y := (maxvalue * y) / (h3 - 1)
		if ev.win = rw
		   then defs[1].red := y
			defs[4].red := y
		 elseif ev.win = gw
		   then defs[2].green := y
			defs[4].green := y
		 else defs[3].blue := y
		      defs[4].blue := y
		 end
		x_display$store_colors(defs)
		rgb := ""
	 elseif ~tracking  cand  ev.kind = ButtonPressed
	   then value: int := basevalue
		if ev.value = LeftButton
		   then value := -value end
		if ev.win = rw
		   then defs[1].red := int$min(int$max(defs[1].red + value,
						       0),
					       maxvalue)
			defs[4].red := defs[1].red
		 elseif ev.win = gw
		   then defs[2].green := int$min(int$max(defs[2].green + value,
							 0),
						 maxvalue)
			defs[4].green := defs[2].green
		 else defs[3].blue := int$min(int$max(defs[3].blue + value,
						      0),
					      maxvalue)
		      defs[4].blue := defs[3].blue
		 end
		x_display$store_colors(defs)
		value := basevalue
		rgb := ""
	 end
	end
    end rgbdemo