require 'tk'

class TkdControl
  def initialize( canvas )
    @canvas = canvas
    @item = nil
    @coords = []
    @x0, @y0 = 0, 0
  end
  attr_writer :item
  def get_coords
    @coords = []
    a = @item.coords
    while( a != [])
      x = a.shift
      y = a.shift
      @coords.push( [x, y] )
    end
    @coords
  end
  def set_coords
    eval( "@item.coords(" + @coords.flatten.join(',') + ")" )
  end
  def make_control
    @coords.each_index{|i|
      x, y = @coords[i][0], @coords[i][1]
      cont = TkcRectangle.new(@canvas, x-2, y-2, x+2, y+2, 'fill'=>'white')
      cont.addtag('control')
      cont.addtag( i )
    }
  end
  def remove_control
    @canvas.delete('control')
  end
  def plotDown(x, y)
    @canvas.dtag 'selected'
    @canvas.addtag_withtag 'selected', 'current'
    @canvas.raise 'current'
    @x0, @y0 = x, y
  end
  def plotMove(x, y)
    @canvas.move 'selected', x-@x0, y-@y0
    @x0, @y0 = x, y
    i = @canvas.find_withtag('selected').shift.gettags[1]
    @coords[i][0], @coords[i][1] = x, y
    set_coords
  end
  def bind
    @canvas.bind('1', proc{})
    @canvas.bind('B1-Motion', proc{})
    @canvas.itembind('control', '1', proc{|x,y| plotDown x,y }, "%x %y" )
    @canvas.itembind('control', 'B1-Motion', proc{|x,y| plotMove x, y }, "%x %y")
  end
  def get_item( item )
    @item = item
    get_coords
    make_control
    bind
  end
  def get_item_with_cursor
    item = @canvas.find_withtag('current').shift
    get_item( item )
  end
end

c = TkCanvas.new.pack
cont = TkdControl.new( c )
item = TkcLine.new(c, 50, 50, 100, 150, 150, 100, 'width'=>2)
cont.get_item( item )

Tk.mainloop