Dragonfly gem Watermark processor blog snippets

after.rb

photograph.original.thumb('640x480>').watermark

before.rb

photograph.original.thumb('640x480>')

dragonfly-initializer.rb

# ... other initialization stuff above here ...

Dragonfly[:images].processor.register(Watermark)

# optional, but gives you the ability to use watermark(opacity: 50)
# rather than process(:watermark, opacity: 50) 
Dragonfly[:images].configure do |c|
  c.job(:watermark) { |*args| process(:watermark, *args) }
end

watermark.rb

class Watermark
  include Configurable
  include ImageMagick::Utils

  def watermark(source_image, opts = {})
    opts = defaults.merge(opts)

    # uses the source image dimensions to resize the watermark with
    image_properties = identify(source_image)
    watermark_resize = "#{image_properties[:width]}x#{image_properties[:height]}^"

    # assembles an ImageMagick convert command which does all the work
    convert(
        source_image,
        "( #{opts[:watermark]} -resize #{watermark_resize} ) -compose dissolve -define compose:args=#{opts[:opacity]} -composite"
    )
    # as you can see the convert syntax is somewhat inscrutable, which is why
    # it's called ImageMagick and not ImageObvious
  end

  def defaults
    {
        opacity: 60, # 0-100 where 0 is opaque
        watermark: File.new("watermark-logo.png").path # a path to a default watermark image
    }
  end
end