test.js

// e.g.
//  mozjs -e "load('Box2D_v2.2.1_min.wasm.js')" test.js

Box2D().then(function(Box2D) {
  function clock() {
    return Date.now();
  }

  var DEBUG = 1;

  var WARMUP = 64;
  var FRAMES = 256;
  var ITERATIONS = WARMUP + FRAMES;

  var e_count = 40;

  function bench() {
    var gravity = new Box2D.b2Vec2(0.0, -10.0);

    var world = new Box2D.b2World(gravity);
    world.SetAllowSleeping(false);

    var bd = new Box2D.b2BodyDef();
    var ground = world.CreateBody(bd);

    var shape0 = new Box2D.b2EdgeShape();
    shape0.Set(new Box2D.b2Vec2(-40.0, 0.0), new Box2D.b2Vec2(40.0, 0.0));
    ground.CreateFixture(shape0, 0.0);

    var topBody;

    var a = 0.5;
    var shape = new Box2D.b2PolygonShape();
    shape.SetAsBox(a, a);

    var x = new Box2D.b2Vec2(-7.0, 0.75);
    var y = new Box2D.b2Vec2();
    var deltaX = new Box2D.b2Vec2(0.5625, 1);
    var deltaY = new Box2D.b2Vec2(1.125, 0.0);

    for (var i = 0; i < e_count; ++i) {
      y.set_x(x.get_x());
      y.set_y(x.get_y());

      for (var j = i; j < e_count; ++j) {
        var bd = new Box2D.b2BodyDef();
        bd.set_type(Box2D.b2_dynamicBody);
        bd.set_position(y);
        var body = world.CreateBody(bd);
        body.CreateFixture(shape, 5.0);

        topBody = body;

        y.op_add(deltaY);
      }

      x.op_add(deltaX);
    }

    var times = []
    for (var i = 0; i < ITERATIONS; ++i) {
      var start = clock();
      world.Step(1.0/60.0, 3, 3);
      var end = clock();
      times.push(end - start);
      if (DEBUG) print([topBody.GetPosition().get_x(), topBody.GetPosition().get_y()]);
    }

    // Slice off the warmup frames.
    times = times.slice(WARMUP)
    print(times);

    var total = 0;
    for (var i = 0; i < times.length; ++i) {
      total += times[i];
    }
    print(total/FRAMES);
  }

  bench();
});