require 'tk'

class TkMove
  def initialize( canvas )
    @x0, @y0 = 0, 0
    @canvas = canvas
    @tag = 'item'
  end

  def bind
    @canvas.itembind( @tag, '1', proc{|x, y| plotDown x, y},"%x %y")
    @canvas.itembind( @tag, 'B1-Motion', proc{|x, y| plotMove x, y},"%x %y")
  end
  def unbind
    @canvas.itembind( @tag, '1', proc{} )
    @canvas.itembind( @tag, 'B1-Motion', proc{} )
  end

  def plotDown(x, y)
    @canvas.dtag 'selected'
    tag = @canvas.gettags('current')[-2]
    @canvas.addtag_withtag 'selected', tag
    @canvas.raise tag
    @x0, @y0 = x, y
  end
  def plotMove(x, y)
    @canvas.move 'selected', x - @x0, y - @y0
    @x0, @y0 = x, y
  end
end

c = TkCanvas.new.pack
m = TkMove.new( c )
m.bind

x1, y1 = 100, 100
item1 = TkcRectangle.new(c, x1-15, y1-15, x1+15, y1+15, 'fill'=>'white')
item1.addtag('item'); item1.addtag('g1')
x2, y2 = 100, 100
item1 = TkcOval.new(c, x2-10, y2-10, x2+10, y2+10, 'fill'=>'red')
item1.addtag('item'); item1.addtag('g1')
x3, y3 = 150, 100
item1 = TkcOval.new(c, x3-10, y3-10, x3+10, y3+10, 'fill'=>'yellow')
item1.addtag('item')
x4, y4 = 200, 100
item1 = TkcOval.new(c, x4-10, y4-10, x4+10, y4+10, 'fill'=>'blue')
item1.addtag('item'); item1.addtag('g2')
Tk.mainloop