circles

Author: monkstone

contributed/circles.rb

@@ -0,0 +1,108 @@
+# 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
+
+# JRubyArt version by Martin Prout
+PBisector = Struct.new(:vector, :angle) # perpendicular bisector
+Vect = Struct.new(:x, :y, :z) # for calculation of center
+
+def settings
+  size(800, 400, P2D)
+end
+
+def setup
+  sketch_title 'Circles From Three Moving Points'
+  color_mode(HSB, 360, 100, 100, 100)
+  @c = rand(360)
+  @points = (0..2).map { Point.new(rand(width), rand(height)) }
+  background 0
+end
+
+def draw
+  fill(0, 0, 0)
+  noStroke
+  rect(0, 0, width, height) if (frame_count % 8_000).zero?
+  @points.each do |point|
+    # change direction sometimes
+    point.set_dir rand(-PI..PI) if rand > 0.96
+    point.update
+    point.check_edges
+  end
+  # set the style of the circle
+  @dc = map1d(millis, 0..150_000, 0..360) # slowly changes hue
+  stroke((@c + @dc) % 360, 50, 100, 5)
+  no_fill
+  # verifies if there is a circle and draw it
+  return if collinear(@points[0].pos, @points[1].pos, @points[2].pos)
+  draw_circle @points
+end
+
+def draw_circle(pts)
+  # find the bisectors of 2 sides
+  mp = []
+  mp[0] = bisector(pts[0].pos, pts[1].pos)
+  mp[1] = bisector(pts[1].pos, pts[2].pos)
+  center_point = center(mp) # find the center of the circle
+  # calculate the radius
+  radius = center_point.dist(pts[2].pos)
+  # if not collinear display circle
+  ellipse(center_point.x, center_point.y, 2 * radius, 2 * radius)
+end
+
+def bisector(a, b)
+  midpoint = (a + b) / 2.0 # middle of AB
+  theta = atan2(b.y - a.y, b.x - a.x) # inclination of AB
+  PBisector.new(midpoint, theta - HALF_PI)
+end
+
+def collinear(a, b, c)
+  (a - b).cross(b - c).zero?
+end
+
+def center(bisector)
+  # equation of the first bisector (ax - y =  -b)
+  eq = bisector.map do |mp|
+    a = tan mp.angle
+    v = mp.vector
+    Vect.new(a, -1, -1 * (v.y - v.x * a))
+  end
+  # calculate x and y coordinates of the circumcenter
+  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)
+  Vec2D.new(ox,oy)
+end
+
+class Point
+  include Processing::Proxy
+  attr_accessor :pos, :velocity, :acceleration
+
+  def initialize(x, y)
+    @pos = Vec2D.new(x, y)
+    @velocity = Vec2D.new
+    @acceleration = Vec2D.random
+  end
+
+  # change direction
+  def set_dir(angle)
+    # direction of the acceleration is defined by the new angle
+    @acceleration = Vec2D.from_angle(angle)
+    dif = acceleration.angle_between velocity
+    dif = map1d(dif, 0..PI, 0.1..0.001)
+    @acceleration *= dif
+  end
+
+  # update position
+  def update
+    @velocity += acceleration
+    velocity.set_mag(1.5) { velocity.mag > 1.5 } # limit velocity
+    @pos += velocity
+  end
+
+  def check_edges
+    pos.x = constrain(pos.x, 0, width)
+    pos.y = constrain(pos.y, 0, height)
+  end
+end