# shadow.rb

    require 'RMagick'

    # Draw a big red Bezier curve on a transparent background.
    img = Magick::Image.new(340, 120) {self.background_color = 'none'}
    gc = Magick::Draw.new
    gc.fill('none')
    gc.stroke('red')
    gc.stroke_linecap('round')
    gc.stroke_width(10)
    gc.bezier(20, 60, 20,-90, 320,210, 320,60)
    gc.draw(img)

    # Composite it onto a white background, draw a border around the result,
    # write it to the "before" file.
    before = img.copy
    bg = Magick::Image.new(before.columns, before.rows) {self.background_color='white'}
    before = bg.composite(before, Magick::CenterGravity, Magick::OverCompositeOp)
    before.border!(1,1,'gray80')
    before.write('shadow_before.gif')

    # Create the shadow.
    shadow = img.shadow()
    # Composite the original image over the shadow, composite the result
    # onto a white background, add a border, write it to the "after" file.
    shadow = shadow.composite(img, Magick::NorthWestGravity, Magick::OverCompositeOp)
    bg = Magick::Image.new(shadow.columns, shadow.rows) {self.background_color='white'}
    after = bg.composite(shadow, Magick::CenterGravity, Magick::OverCompositeOp)
    after.border!(1,1,'gray80')

    after.write('shadow_after.gif')

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