Analysers

An Analyser analyses a particular property of a piece of content, e.g. the width of an image, the bitrate of an audio file, etc.

One can be added using a block

Dragonfly.app.configure do
  analyser :depth do |content|
    # ...
  end
  # ...
end

or providing an object that responds to call (MyAnalyser in this case)

Dragonfly.app.configure do
  analyser :depth, MyAnalyser
  # ...
end

Using the analyser

The analyser is available as a method to Job objects

image = Dragonfly.app.fetch('some/uid')
image.depth

and Attachment objects

image = my_model.photo
image.depth

Implementing the analyser

The content object yielded to the block/call method is a Dragonfly::Content - see the doc for methods it provides.

Returning the property

Simply return the calculated property. You will probably want to use one of the Content methods for getting the data such as data (String), file, path, etc.

analyser :depth do |content|
  SomeLibrary.get_depth(content.data)
end

Using shell commands

To use the shell, you can use Content#shell_eval

analyser :depth do |content|
  content.shell_eval do |path|
    "/usr/bin/get_depth #{path}"  # The command sent to the command line
  end
end

The yielded path above will always exist.

Using pre-registered analysers

To use a pre-registered analyser, use Content#analyse

analyser :bytes_per_pixel do |content|
  num_pixels = content.analyse(:width) * content.analyse(:height)
  content.size.to_f / num_pixels
end

ImageMagick

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

“Magic” Model Attributes

To automatically store analysed properties in your model see Models - Magic Attributes