bounce.rb

class Bouncer
  def initialize xvelocity, yvelocity, canvas
    @xvelocity = xvelocity
    @yvelocity = yvelocity
    @canvas = canvas
  end

  def update target
    if (Canvas.get_left(target) + @xvelocity) >= (@canvas.actual_width - target.width)  or (Canvas.get_left(target) + @xvelocity) <= 0
      @xvelocity = -@xvelocity
    end
    if (Canvas.get_top(target)  + @yvelocity) >= (@canvas.actual_height - target.height) or (Canvas.get_top(target)  + @yvelocity) <= 0
      @yvelocity = -@yvelocity
    end
    Canvas.set_top  target, Canvas.get_top(target)  + @yvelocity
    Canvas.set_left target, Canvas.get_left(target) + @xvelocity
  end
end

def each_object target
  Bouncer.new rand(10) - 5, rand(10) - 5, canvas
end

lots-o-squares.rb

# create a ton of random sized, colored, and stroked rectangles

include System::Windows::Shapes
include System::Windows::Media
include System::Windows::Controls

canvas.children.clear
colors = %W(red orange yellow lime blue purple violet)
brushes = colors.map{|c| SolidColorBrush.new(Colors.send(c)) }
canvas_dim = lambda{ [canvas.actual_width, canvas.actual_height] }

500.times do
  size = rand(canvas_dim[].max / 10)
  shape = Rectangle.new
  shape.width, shape.height = size, size
  shape.fill = brushes[rand brushes.size]
  shape.stroke = brushes[rand brushes.size]
  shape.stroke_thickness = rand(canvas_dim[].max / 70) + 4
  canvas.children.add shape
  Canvas.set_left shape, rand(canvas_dim[].first - size)
  Canvas.set_top  shape, rand(canvas_dim[].last  - size)
end

without-host-help.rb

# Load the DLLs that allow you work with graphics
require 'PresentationCore, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'
require 'PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'

# Get the window and canvas from the host application
window = System::Windows::Application.current.main_window
canvas = window.find_name('_canvas')