{Software} Structures

/* 
 
   Structure 3 (work in progress) 
   
   A surface filled with one hundred medium to small sized circles. 
   Each circle has a different size and direction, but moves at the same slow rate. 
   Display: 
   A. The instantaneous intersections of the circles 
   B. The aggregate intersections of the circles 
 
   Ported to p5.js by Casey Reas
   11 July 2016
   p5.js 0.5.2
  
   Restored by Casey Reas <http://reas.com> 
   22 June 2016 
   Processing v.3.1.1 <http://processing.org> 
  
   Implemented by Casey Reas 
   Uses circle intersection code from William Ngan <http://metaphorical.net> 
   Processing v.68 <http://processing.org> 
 
*/

var circleA, circleB;

function setup() {
  createCanvas(300, 300);
  frameRate(30);
  circleA = new Circle(150, 150, 60);
  circleB = new Circle(150, 150, 90);
  noStroke();
  background(204);
}

function draw() {
  circleA.update();
  circleB.update();
  intersect(circleA, circleB);
}

function Circle(px, py, pr) {
  this.x = px;
  this.y = py;
  this.r = pr;
  this.r2 = this.r * this.r;
  this.xspeed = random(-2, 2);
  this.yspeed = random(-2, 2);
  this.xdir = 1;
  this.ydir = -1;

  this.update = function() {

    this.x += this.xspeed * this.xdir;
    if (this.x > width - this.r || this.x < this.r) {
      this.xdir = this.xdir * -1;
    }

    this.y += this.yspeed * this.ydir;
    if (this.y > width - this.r || this.y < this.r) {
      this.ydir = this.ydir * -1;
    }

  }
}

function intersect(cA, cB) {

  var dx = cA.x - cB.x;
  var dy = cA.y - cB.y;
  var d2 = dx * dx + dy * dy;
  var d = sqrt(d2);

  if ((d > cA.r + cB.r) || (d < abs(cA.r - cB.r))) {
    return; // no solution 
  }

  var a = (cA.r2 - cB.r2 + d2) / (2 * d);
  var h = sqrt(cA.r2 - a * a);
  var x2 = cA.x + a * (cB.x - cA.x) / d;
  var y2 = cA.y + a * (cB.y - cA.y) / d;

  var paX = x2 + h * (cB.y - cA.y) / d;
  var paY = y2 - h * (cB.x - cA.x) / d;
  var pbX = x2 - h * (cB.y - cA.y) / d;
  var pbY = y2 + h * (cB.x - cA.x) / d;

  stroke(0, 26);
  line(paX, paY, pbX, pbY);

}