Shuffle.js

planck.testbed('Shuffle', function(testbed) {
  var pl = planck, Vec2 = pl.Vec2, Math = pl.Math;

  var SPI4 = Math.sin(Math.PI / 4), SPI3 = Math.sin(Math.PI / 3);

  var width = 10.00, height = 10.00;

  var BALL_R = 0.3;
  var BALL_D = 1;

  testbed.x = 0;
  testbed.y = 0;
  testbed.width = width * 1.5;
  testbed.height = height * 1.5;
  testbed.ratio = 50;
  testbed.mouseForce = -100;

  pl.internal.Settings.velocityThreshold = 0;

  var world = pl.World({});

  var walls = [
    Vec2(-width * .5, -height * .5),
    Vec2(-width * .5, +height * .5),
    Vec2(+width * .5, +height * .5),
    Vec2(+width * .5, -height * .5)
  ];

  var wallFixDef = {
    userData : 'wall'
  };
  var ballFixDef = {
    friction: 0.1,
    restitution: 0.98,
    density: 0.8,
    userData : 'ball'
  };
  var ballBodyDef = {
    bullet: true,
    linearDamping : 1.6,
    angularDamping : 1.6
  };

  world.createBody().createFixture(pl.Chain(walls, true), wallFixDef);

  row(1, 8, BALL_R, BALL_D).map(translate(height * 0.4, 0)).forEach(function(p) {
    var ball = world.createDynamicBody(ballBodyDef);
    ball.setPosition(p);
    ball.setAngle(Math.PI);
    ball.createFixture(pl.Circle(BALL_R), ballFixDef);
    ball.render = {fill : '#ff411a', stroke: 'black'};
  });

  row(1, 8, BALL_R, BALL_D).map(translate(-height * 0.4, 0)).forEach(function(p) {
    var ball = world.createDynamicBody(ballBodyDef);
    ball.setPosition(p);
    ball.createFixture(pl.Circle(BALL_R), ballFixDef);
    ball.render = {fill : '#0077ff', stroke: 'black'};
  });

  world.on('post-solve', function(contact) {
    var fA = contact.getFixtureA(), bA = fA.getBody();
    var fB = contact.getFixtureB(), bB = fB.getBody();

    var wall = fA.getUserData() == wallFixDef.userData && bA || fB.getUserData() == wallFixDef.userData && bB;
    var ball = fA.getUserData() == ballFixDef.userData && bA || fB.getUserData() == ballFixDef.userData && bB;

    // do not change world immediately
    setTimeout(function() {
      if (ball && wall) {
        world.destroyBody(ball);
      }
    }, 1);
  });

  return world;

  function row(n, m, r, l) {
    var d = r * 2;
    var balls = [];
    for (var i = 0; i < n; i++) {
      for (var j = 0; j < m; j++) {
        balls.push(Vec2(i * l - (n - 1) * .5 * l + Math.random(r * 0.02), j * l - (m - 1) * .5 * l + Math.random(r * 0.02)));
      }
    }
    return balls;
  }

  function scale(x, y) {
    return function (v) {
      return pl.Vec2(v.x * x, v.y * y);
    };
  }

  function translate(x, y) {
    return function (v) {
      return pl.Vec2(v.x + x, v.y + y);
    };
  }

});