RComposite

RComposite is an RMagick abstraction library to easily manipulate and composite images through the use of a canvas, layers, layer masks, adjustment layers, fill layers, and layer sets (much like in Photoshop).

Install:

Add the github repository to your gem sources:

sudo gem sources -a http://gems.github.com

Install the gem from github:

sudo gem install corbanbrook-rcomposite

Require:

require 'rubygems'
require 'rcomposite'

include RComposite # optional: if you wish to have the RComposite module in your project scope

...

Class Summary:

• Layers: There are 4 types of Layer Models,

  • Layer: The base layer model. Can load an image from disk, blob, or RMagick Image object. Contains methods to transform, change layer mode, change opacity level, and more.

  • FillLayer: A solid color, gradient, or pattern fill layer.

  • AdjustmentLayer: Invert, Threshold, Levels, Blur adjustment layer. Applies layer effect over everything under it in the layer stack.

  • LayerMask: Mask any of the above layer types. LayerMasks are a special type of layer which is a Alpha Channel mask that can be applied to any layer type. Since LayerMask is also a layer, it can also be transformed in any way.

  • LayerSets: 2 types of LayerSet Models,

    • LayerSet: The LayerSet is a container, or directory in which to bundle layers. LayerSet contains methods to do group transforms on its bundled layers. Transforms like rotation, movement and scaling are performed on all the layers it contains while maintaining each layer on a seperate plane without merging.

    • Canvas: The canvas is a special LayerSet which is a blank workspace containing other layers and layer sets.

Usage:

• Creating a blank canvas:

  canvas = RComposite::Canvas.new(640, 480)
  

  Canvas also accepts an optional block for easily adding layers to the stack

  canvas = Rcomposite::Canvas.new(640, 480) do
    layer :file => 'butterfly.png'
  end
  

• Creating a layer:

  photo = RComposite::Layer.new :file => 'photo.jpg'
  

• Creating a fill layer:

  blue = RCompisite::FillLayer.new '#000090'
  

• Changing a Layers properties:

  blue.opacity 40
  blue.mode Multiply
  

• Adding layers to the canvas. (Whatever is added first will be on top):

  canvas.layer blue
  canvas.layer photo
  

• Saving the canvas:

  canvas.save_as 'bluesky.jpg'
  

• Adding an alpha channel mask to a layer:

  Masks are used to punch holes into layers to add transparency.

  blue.layer_mask :file => 'alpha_channel.png'
  

  You can add layer options to the mask just like it was a normal layer.

  fill_layer SolidColor, '#f83898FF' do
    layer_mask :file => 'butterfly-mask.png' do
      offset -30, -30
      rotate 40
    end
  end
  

The real power of RComposite lies in its use of blocks and simplified syntax. Take a look at the following examples:

• Just like the Canvas, all layer types also accept an optional block parametre for setting layer options:

  butterfly = RComposite::Layer :file => 'butterfly.png' do 
    offset 100, 100 # moves the layer on the canvas
    rotate 25
  end
  

  or..

  canvas.layer :file => 'butterfly.png' do 
    ..
  end
  

• DSL Example

  Canvas.new(320,240) do
  
    layer_set :slides do
      layer :file => 'slide1.png' do
        opacity 65
        offset 12, 12
        mode Lighten
      end
  
      adjustment_layer Blur, 0.5, 1.5 do
        layer_mask :file => 'butterfly-mask.png'
      end
  
      layer :file => 'slide2.png' do
        offset 28, 28
        opacity 30
        mode Darken
      end
  
      rotate 45
      offset 70, 50
      scale 80, 80
    end
  
    fill_layer SolidColor, '#f83898FF' do
      opacity 70
      mode Multiply
  
      layer_mask :file => 'butterfly-mask.png' do
        offset -30, -30
        image.rotate! 40
      end
    end
  
    fill_layer Gradient, 0, 0, 0, 50, '#606', '#033' do
      opacity 90
      mode Overlay
  
      layer_mask :file => 'butterfly-mask.png' do
        offset -20, -20
      end
    end
  
    layer :file => 'background.png' do
      image.resize!(320, 240)
    end
  
    save_as 'composite.jpg'
  end
  

The nice thing about RComposite is that it doesnt hide the underlaying RMagick Image object from you. It is always available through the image accessor

layer :file => 'photo.jpg' do
  image.crop_resized!(100,300) # crop_resized! is a RMagick method
end

@corban weare.buildingsky.net __

Copyright (c) 2009 Corban Brook, released under the MIT license