Generators

A Generator creates content from nothing, e.g. text image generation, sine-wave audio generation for a given note, etc.

They work in exactly the same way as processors, except the content they receive is empty.

They can be added using a block or object that responds to call

Dragonfly.app.configure do
  generator :text do |content, *args|
    # ...
  end

  generator :sine_wave, SineWaveGenerator.new
  # ...
end

Using the generator

Calling the generator on the app creates a new Job object

job = Dragonfly.app.generate(:sine_wave, 'c')

Implementing the generator

Implementing is the same as for processors (including update_url) - see Processors and Dragonfly::Content.

Using shell commands

To generate using the shell, you can use Content#shell_generate

generator :sine_wave do |content, note|
  content.shell_generate :ext => 'wav' do |path|  # :ext is optional
    "/usr/local/bin/sine_wave -note #{note} -out #{path}"
  end
end

The yielded path above will always exist.

Using pre-registered generators

To generate using a pre-registered generator, use Content#generate!

generator :gradient do |content|
  content.generate! :convert, "-size 100x100 gradient:blue", 'jpg'
end

ImageMagick

The ImageMagick plugin adds a few generators - see the doc for more details.

If you’re defining a new generator you can make use of the generate command in Dragonfly::ImageMagick::Commands, e.g.

include Dragonfly::ImageMagick::Commands

generator :fancy do |content|
  generate(content, '-size 100x100 gradient:blue', 'jpg')
end

which corresponds to the command-line

convert -size 100x100 gradient:blue <path>

where path has extension ‘jpg’ (optional argument).