Extending Compass

Sprite engine

The sprite engine is the work horse of sprite generation it's the interface for assembling and writing the image file to disk.

Requirements

A sprite engine requires two methods construct_sprite, and save(filename)

Once inside the class you have access to images which is a collection of Compass::SassExtensions::Sprites::Image

Configuration

To enable your sprite engine from the config file set

sprite_engine = :<engine name>

The example below will load Compass::SassExtension::Sprites::ChunkyPngEngine.new(width, height, images)

sprite_engine = :chunky_png

Class Definition

module Compass
  module SassExtensions
    module Sprites
      class ChunkyPngEngine < Compass::SassExtensions::Sprites::Engine

        def construct_sprite
          #do something
        end    

        def save(filename)
          #save file
        end

      end
    end
  end
end

Adding Configuration Properties to Compass

To add a new configuration property to Compass:

Compass::Configuration.add_configuration_property(:foobar, "this is a foobar") do
  if environment == :production
    "foo"
  else
    "bar"
  end
end

This will do several things:

1. make it possible for users to set the foobar configuration property in their configuration file.
2. Ruby code can read and write the foobar attribute from any configuration object.
3. It will add the comment # this is a foobar above the property in the configuration file. A comment is not required, you can simply omit this argument if you like.
4. The block of code provided allows you to assign a sensible default value according to other settings in the configuration or by using arbitrary code to determine what the value should be. For instance it could read from another configuration file or it could change based on the user's operating system.