require 'tkmove3.rb'
include TestBed

c = TkCanvas.new.pack
testbed( c )

x0, y0 = 150, 100
TkcOval.new(c, x0-4, y0-4, x0+4, y0+4, 'fill'=>'yellow').addtag('center')
f = TkFrame.new.pack
TkButton.new(f, 'text'=>'addtag_closest', 'command'=>proc{
  c.delete('center')
  c.addtag_closest( 'closest', x0, y0 )
  item = c.find_withtag('closest').shift
  if item != nil
    item.fill('blue')
  end
  TkcOval.new(c, x0-4, y0-4, x0+4, y0+4, 'fill'=>'yellow').addtag('center')
  c.dtag('closest')
}).pack('side'=>'left')

Tk.mainloop