Procedural circle

procedural_circle.rb

# Based on https://codepen.io/clawtros/pen/yVONbR

require 'graphics'

SIZE = 0.5

Node = Struct.new :x, :y, :∆x, :∆y, :color, :lifespan, :on_death do
  def successor
    new∆x = ∆x*0.98 + (rand - 0.5) / 2
    new∆y = ∆y*0.98 + (rand - 0.5) / 2
    Node.new x+new∆x, y+new∆y,
             new∆x,   new∆y,
             color,
             lifespan-1,
             on_death
  end

  def draw(canvas)
    canvas.line x, y, x+∆x, y+∆y, color
  end

  def alive?
    0 <= lifespan
  end
end


class Velo < Graphics::Simulation
  include Math
  attr_accessor :nodes

  def initialize(width, height)
    super width, height, 24
    color.default_proc = -> h, k { k }
    self.nodes = 0.step(by: 2*PI/width, to: 2*PI).map do |angle|
      x = cos(angle) * height / 5
      y = sin(angle) * height / 5
      Node.new x + width/2, y + height/2,
               0, 0,
               [255, 0, 0],
               10_000 * rand,
               :explode
    end
  end

  def update(n)
    self.nodes = nodes.each_with_object([]) do |node, new_nodes|
      successor = node.successor
      if successor.alive?
        new_nodes << successor
      elsif successor.on_death == :explode
        rand(20).times do
          new_nodes << Node.new(
            node.x,                 node.y,
            node.∆x + (rand - 0.5), node.∆y + (rand - 0.5),
            [255, 255, 255],
            (100 * rand).to_i,
            :nothing
          )
        end
      end
    end
  end

  def draw(n)
    nodes.each { |node| node.draw self }
  end
end

Velo.new(1200, 900).run