Context free art in ruby in 3d in opengl

Since I'm a fan of contextfreeart.org and nodebox.net, I've made a small ruby program inspired by contextfreeart, using context free grammars in 3d with opengl. The only operations right now are:

• cube - create a cube.
  
• up/down/left/right/to/from(rule) - define what rule to continue with in the specified direction.
  
• flip - rotate 90 degress
  
• scale - scale with 0.9.
  

But it should be quite easy to add new primitives (and clean up the code). Here is an example of a tree. Install ruby-opengl gem, click and move mouse to rotate, q - new random seed value, w - increase rendering depth, e - decrease rendering depth.

load 'cfa3d.rb'
class Tree < CFG
  rule :start do |s|
    s.cube
    s.up :x
  end

  rule :x do |s|
    s.cube
    s.right :x
  end
  rule :x do |s|
    s.cube
    s.flip
    s.left :x
  end
  rule :x, 0.1 do |s|
    s.cube
    s.flip
    s.right :x
    s.flip
    s.left :x
  end
  rule :x do |s|
    s.cube
    s.scale
    s.up :x
  end
end

render Tree