# File gtk/sample/misc/mouse-gesture.rb, line 163
  def start(widget, button, x, y, base_x, base_y)
    Gtk.grab_add(self)
    @widget = widget
    @button = button
    @processor.start(x, y)
    @base_x = base_x
    @base_y = base_y
    @cr = window.create_cairo_context
    @cr.set_source_rgba(@line_rgba)
    @cr.move_to(x, y)
  end