    #! /usr/local/bin/ruby -w
    require 'RMagick'

    i = Magick::ImageList.new
    i.new_image(400, 400) { self.background_color = "white" }

    gc = Magick::Draw.new

    gc.font('Helvetica').pointsize(128)

    # Draw large black percentages
    gc.text( 10,140,"'100'")
    gc.text(235,140,"'80'")
    gc.text( 35,340,"'60'")
    gc.text(235,340,"'40'")

    # Establish the stroke and fill parameters
    gc.stroke("'blue'").stroke_width(10).stroke_linejoin('round')
    gc.fill('yellow')

    # For each of the 4 opacity levels, draw a blue-rimmed
    # yellow triangle over the corresponding number.
    # Note that the opacity argument can be either a number
    # between 0 and 1
    gc.opacity('100%')   or 1.00
    gc.polygon(25,175, 175, 25, 25,25)
    gc.opacity('80%')    or 0.80
    gc.polygon(225,175, 375,25, 225,25)
    gc.opacity(0.60)     or '60%'
    gc.polygon( 25,375, 175, 225, 25,225)
    gc.opacity(0.40)     or '40%'
    gc.polygon(225,375, 375,225, 225,225)

    gc.draw(i)
    #i.display
    i.write("opacity.gif")