Using libraries from processing-3.0a4 in ruby processing

Up to and including processing-2.2.1 the path to sketchbook was/is discovered by "reading" the preferences.txt configuration file for ruby processing. For processing-3.0a4 the name has changed (to allow different libraries/sketches to co-exist for different versions?). For processing-3.0a4 you can set the "sketchbook_path" in the ".rp5rc" file, works for me on linux see yaml file below (will override preferences.txt value).

---
PROCESSING_ROOT: /home/tux/processing-3.0a4
JRUBY: "true"
sketchbook_path: /home/tux/sketchbook

New features in ruby-processing-2.6.2

# Hooky class demonstrates how to use the post_initialize hook,
# available since ruby-processing-2.6.2, to add additional attribute
# in this case :background as an array of int (splat to color)
# Not sure how clever it is to have multiple sketch instances.

class Hooky < Processing::App
  attr_reader :back

  def setup
    size 200, 200
    background(*back)
  end

  def post_initialize(args)
    @back = (args[:background])
  end
end

red = [200, 0, 0]
green = [0, 200, 0]
blue = [0, 0, 200]
colors = [red, green, blue]

colors.each_with_index do |col, i|
  Hooky.new(x: i * 90, y: i * 90, title: "Hooky #{i}", background: col)
end

Read more about post-initialization hooks in POODR by Sandi Metz.