Flickering rectangle

flicker_in_screen.rb

require 'java'
require 'swt'

module Swt
  include_package 'org.eclipse.swt'
  include_package 'org.eclipse.swt.layout'
  include_package 'org.eclipse.swt.widgets'
  include_package 'org.eclipse.swt.graphics'
  include_package 'org.eclipse.swt.events'
end

class Object
  include Swt
end

class Rect
  def initialize x, y
    @x, @y = x, y
  end
  attr_accessor :x, :y
end

class Anim
  def initialize display, cs, &blk
    @display, @cs, @blk = display, cs, blk
  end
  def run
    @blk.call
    @cs.redraw
    @display.timerExec 10, self
  end
end

display = Swt::Display.new
shell = Swt::Shell.new display
shell.setSize 200+16, 500+38
cs = Swt::Composite.new shell, Swt::SWT::NONE
cs.setSize 600, 500

def rect_paint_control display, cs, rects
  pl = Swt::PaintListener.new
  class << pl; self end.
  instance_eval do
    define_method :paintControl do |e|
      gc = e.gc
      gc.setAntialias Swt::SWT::ON
      gc.setBackground Swt::Color.new(display, 95, 158, 160)
      rects.each do |s|
        gc.fillRoundRectangle s.x, s.y, 50, 50, 0, 0
      end
    end
  end
  cs.addPaintListener pl
end

def anim display, cs, &blk
  Anim.new(display, cs, &blk).tap do |a|
    display.timerExec 10, a
  end
end

rects = [Rect.new(50, 0)]

rect_paint_control display, cs, rects

i = 0
anim display, cs do
  rects.each{|r| r.y = i % 500}
  i += 1
end

shell.open

while !shell.isDisposed do
  display.sleep unless display.readAndDispatch
end
display.dispose

I'm looking for a solution to reduce flicker in screen.
Try out this snippet with your JRuby and SWT.