New contributed example, from OpenProcessing.

Author: poqudrof

contributed/circles.rb

@@ -0,0 +1,140 @@
+#!/usr/bin/env jruby
+# coding: utf-8
+require 'propane'
+
+## Circles by Bárbara Almeida
+##  A fork of Circle through 3 points by Bárbara Almeida.
+## Draw circles from 3 points moving on smooth random trajectories.
+## https://www.openprocessing.org/sketch/211167
+
+## Propane version by Jérémy Laviole - @poqudrof
+
+class Circles < Propane::App
+
+  def settings
+    size(800, 600, P3D)
+  end
+  
+  ## To be overriden by the Presentation Code.
+  def setup
+    colorMode(HSB, 360, 100, 100, 100);
+    @c = random(360);
+
+    @points = []
+    3.times { @points << Points.new(random(width),random(height)) }
+
+    background 0
+    @setup_done = true
+  end
+
+  def draw
+    fill(0, 0, 0);
+    noStroke
+
+    if (frameCount % 8000 == 0)
+      rect(0, 0, width, height);
+    end
+    
+    @points.each do |point|
+      ##change direction sometimes  
+      point.setDir random(-Propane::PConstants::PI, Propane::PConstants::PI) if (random(1) > 0.96)
+      point.update
+      point.checkEdges
+    end
+
+    ## set the style of the circle
+    @dc = Propane::PApplet::map(millis(), 0, 150000, 0, 360) ## slowly changes hue
+    stroke((@c + @dc) % 360, 50, 100, 5)
+    noFill
+  
+  ## verifies if there is a circle and draw it
+    
+    det = (@points[0].p.x * @points[1].p.y)  + (@points[1].p.x * @points[2].p.y) + (@points[2].p.x * @points[0].p.y);
+
+    det -= (@points[0].p.y * @points[1].p.x)  + (@points[1].p.y * @points[2].p.x) + (@points[2].p.y * @points[0].p.x);
+
+
+    draw_circle @points if Propane::PApplet::abs(det) > 50
+  end
+
+
+  def draw_circle(pts)
+
+    ## find the midpoints of 2 sides
+    mp = []
+    mp[0] = midpoint(pts[0].p, pts[1].p);
+    mp[1] = midpoint(pts[1].p, pts[2].p); 
+
+    center_point = center(mp);   ## find the center of the circle
+    r = dist(center_point.x, center_point.y, pts[2].p.x, pts[2].p.y);  ##calculate the radius
+      
+    ellipse(center_point.x, center_point.y, 2*r, 2*r); ## if not collinear display circle  
+  end
+
+  def midpoint(a, b)
+    d = dist(a.x, a.y, b.x, b.y); ## distance AB
+    theta = atan2(b.y - a.y, b.x - a.x); ## inclination of AB
+    p = Propane::PVector.new(a.x + d/2*  Propane::PApplet::cos(theta),
+                    a.y + d/2* Propane::PApplet::sin(theta), # midpoint
+                    theta - Propane::PConstants::HALF_PI);  #inclination of the bissecteur
+    return p
+  end
+
+  def center(mid_point)
+    eq = []
+
+    ## equation of the first bissector (ax - y =  -b)       
+    mid_point.each do |mp|
+      a = tan mp.z
+      eq << Propane::PVector.new(a,
+                                   -1,
+                                   -1*(mp.y - mp.x*a))
+    end
+
+    ## calculate x and y coordinates of the center of the circle
+    ox = (eq[1].y * eq[0].z - eq[0].y * eq[1].z) /
+         (eq[0].x * eq[1].y - eq[1].x * eq[0].y);
+    oy =  (eq[0].x * eq[1].z - eq[1].x * eq[0].z) /
+          (eq[0].x * eq[1].y - eq[1].x * eq[0].y);
+    return Propane::PVector.new(ox,oy);
+  end
+end
+
+
+class Points
+
+  include Propane::Proxy
+  attr_accessor :p, :velocity, :acceleration
+  
+  def initialize(x, y)
+    @p = Propane::PVector.new(x, y, 1)
+    @velocity = Propane::PVector.new(0, 0, 0);
+    @acceleration = Propane::PVector.new($app.random(1), $app.random(1), 0)
+  end
+
+  # change direction
+  def setDir(angle) 
+    ## direction of the acceleration is defined by the new angle
+    acceleration.set(Propane::PApplet::cos(angle), Propane::PApplet::sin(angle), 0); 
+    
+    ## magnitude of the acceleration is proportional to the angle between acceleration and velocity
+    acceleration.normalize
+    dif = Propane::PVector::angleBetween(acceleration, velocity)
+    dif = Propane::PApplet::map(dif, 0, Propane::PConstants::PI, 0.1, 0.001)
+    acceleration.mult(dif);
+  end
+
+  ## update position
+  def update
+    velocity.add(acceleration);
+    velocity.limit(1.5);    
+    p.add(velocity);
+  end
+  
+  def checkEdges
+    p.x = constrain(p.x, 0, $app.width)
+    p.y = constrain(p.y, 0, $app.height)
+  end
+end
+
+Circles.new