var numBalls = 10;

var damp = 15;

var radius = 12;

var simulationIters = 10;

var simSpeed = 0.5;

var wind = 5;

​

function setup() {

  createCanvas(400, 400);

  for(var i = 0; i < numBalls; i++) {

    sphericles.push([Math.random() * width,

                     Math.random() * height, 0, 0]);

  }

}

​

function draw() {

  background(235);

  fill(200, 120, 30);

  noStroke();

  // collisions

  for(var i = 0; i < sphericles.length; i++) {

    var [x, y, vx, vy] = sphericles[i];

    circle(x, y, radius*2);

  }

  for(var it = 0; it < simulationIters; it++) {

    for(var i = 0; i < sphericles.length; i++) {

      var [x, y, vx, vy] = sphericles[i];

​

      //acceleration

      // gravity

      sphericles[i][3] += 0.4 * simSpeed/simulationIters;

      // wind

      sphericles[i][2] += wind*(noise(millis()*10+i*100) - 

                           0.5) * simSpeed/simulationIters;

​

      // integration

      sphericles[i][1] += sphericles[i][3] * simSpeed/simulationIters;

      sphericles[i][0] += sphericles[i][2] * simSpeed/simulationIters;

​

      // damping

      sphericles[i][2] = constrain(sphericles[i][2],

                                   -damp, damp);

      sphericles[i][3] = constrain(sphericles[i][3],

                                   -damp, damp);

    }

    collisions();

  }

}

​

function collisions() {

  // bounds checking

  for(var i = 0; i < sphericles.length; i++) {

    // walls

    if(sphericles[i][0] > width-radius || sphericles[i][0] < radius) {

      sphericles[i][0] = constrain(sphericles[i][0],

                                   radius, width-radius);

      sphericles[i][2] *= -1;

    }

    // floor/ceiling

    if(sphericles[i][1] > height-radius || sphericles[i][1] < radius) {

      sphericles[i][1] = constrain(sphericles[i][1],

                                   radius, height-radius);

      sphericles[i][3] *= -1;

    }

  }

​

  // other balls

  var newSphericles = sphericles.slice();

  for(var i = 0; i < sphericles.length; i++) {

    var [x1, y1, vx1, vy1] = sphericles[i];

    for(var j = 0; j < sphericles.length; j++) {

      if(i == j) {

        continue;

      }

      var [x2, y2, vx2, vy2] = sphericles[j];

      var dist = sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)/2;

      if(dist < radius) {

        var meanX = (x1 + x2) / 2, meanY = (y1 + y2) / 2;

        var dot2 = vx2 * (x1 - x2) + vy2 * (y1 - y2);

        dot2 /= dist*4 * sqrt(vx2 ** 2 + vy2 ** 2);

        // remove orthogonal component

        var nx2 = (x1-x2) * dot2,

            ny2 = (y1-y2) * dot2;

        var dot1 = vx1 * (x2 - x1) + vy1 * (y2 - y1);

        dot1 /= dist*4 * sqrt(vx1 ** 2 + vy1 ** 2);

        // keep orthogonal component

        var nx1 = (x2-x1) * dot1,

            ny1 = (y2-y1) * dot1;

        newSphericles[i] = [

          meanX + (x1 - meanX) * (radius+0.05) / dist,

          meanY + (y1 - meanY) * (radius+0.05) / dist,

          nx2 + vx1 - nx1,

          ny2 + vy1 - ny1

        ]

      }

    }

  }

  sphericles = newSphericles;

}

​