# opacity.rb

    #!/usr/local/bin/ruby18 -w
    require 'RMagick'

    canvas = Magick::Image.new(260, 125)
    gc = Magick::Draw.new
    gc.fill('black')
    gc.rectangle(10,20, 250,90)

    gc.stroke('blue')
    gc.fill('yellow')
    gc.stroke_width(10)

    gc.opacity('25%')
    gc.roundrectangle(20,20, 60,90, 5,5)

    gc.opacity('50%')
    gc.roundrectangle(80,20, 120,90, 5,5)

    gc.opacity(0.75)
    gc.roundrectangle(140,20, 180,90, 5,5)

    gc.opacity(1)
    gc.roundrectangle(200,20, 240,90, 5,5)

    gc.font_weight(Magick::NormalWeight)
    gc.font_style(Magick::NormalStyle)
    gc.stroke('transparent')
    gc.fill('black')
    gc.gravity(Magick::SouthGravity)
    gc.text(-90,15, '"25%"')
    gc.text(-30,15, '"50%"')
    gc.text( 30,15, '"75%"')
    gc.text( 90,15, '"100%"')

    gc.draw(canvas)
    canvas.write("opacity.png")
    exit

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