#!/usr/koeki/bin/ruby -Ke
require 'tk'

TkCanvas.new {|c|
  width(400)
  height(400)
  cx, cy = c.width/2, c.height/2
  r = 100
  ovl = TkcOval.new(c, cx-r, cx-r, cx+r, cy+r,
                    'fill'=>'yellow', 'outline'=>'black')
  Thread.new {
    while true
      r = (r+8)%(width/2)
      ovl.coords(cx-r, cx-r, cx+r, cy+r)
      sleep 0.0001
    end
  }
}.pack
TkButton.new("text"=>'quit', 'command'=>'exit').pack
Tk.mainloop