Requirements

Requires JRubyArt-1.3.1+ (hence jruby-9.0.8.0+) or propane-2.3.2+

Install the generative gem

jruby -S gem install geomerative # safe way
gem install geomerative # using rvm rbenv to use jruby instead of MRI

Create basic sketch

mkdir 'fred'
mkdir 'fred/data'
cp '/usr/share/fonts/TTF/FreeMono.ttf fred/data' # other fonts are available
# '/usr/share/fonts/TTF/LiberationMono-Bold.ttf' Mac and Windows paths differ
cd fred
k9 create fred 600 400

Edit sketch as follows:-

require 'geomerative'

# Declare the objects we are going to use, so that they are accessible from
# setup and from draw (use '@' prefix in declare)
attr_reader :grp

def setup
  sketch_title 'Fred'
  RG.init(self) # important
  fill(255, 102, 0)
  # you could also use absolute path for fonts, then no need to copy
  @grp = RG.get_text('Hello World!', data_path('FreeMono.ttf'), 72, CENTER)
end

def draw
  background(255)
  translate(width / 2, height / 2)
  grp.draw
end

def settings
  size(600, 400)
end

fred.png

See more refined examples here, and even more here including rotating text and text obeying physics.

Usage with propane is very similar see examples here