「R2Dを使って、リサージュ図形をアニメーションしてみました https://maehrm.hatenablog.com/entry/20140208/p1 」のR2Dがdeprecatedなので、 Ruby2D gem 向けに書き換えたもの。

lissajous-figure-with-ruby2d.rb

# -*- coding: utf-8 -*-
# Originally written by maehrm (id:rahaema) - https://maehrm.hatenablog.com/entry/20140208/p1
require "ruby2d"
include Math

w = Window

class Numeric
  def to_rad
    self*PI/180
  end
end

alpha = 0
exp = ->(deg, alpha) {
  # (x, y) = (cosθ, sin(2θ+α))
  [cos(deg.to_rad)*200+w.width/2, -sin(2*deg.to_rad+alpha.to_rad)*200+w.height/2]
}

update do
  Rectangle.new(x: 0, y: 0, width: w.width, height: w.height, color: 'black')
  Text.new("α = #{alpha}", x: 10, y: 10, size: 30, color: 'green')
  x1, y1 = exp.call(0, alpha)
  5.step(360, 5) {|deg|
    x2, y2 = exp.call(deg, alpha)
    Line.new(x1: x1, y1: y1, x2: x2, y2: y2, width: 2, color: "red")
    x1, y1 = x2, y2
  }
  alpha >= 330 ? alpha = 0 : alpha += 30
end

w.show