Our velocity update function for the sweet new game, "Sassteroids"

sassteroidVelocityUpdate.js

  Sassteroid.prototype.updateVelocity = function (that, maxDimensions) {
    var dotProd = Sassteroids.Utils.dotProduct;

    var perpVec = Array(2);
    var uSpeed = Math.sqrt(dotProd(this.vel, this.vel));
    var vSpeed = Math.sqrt(dotProd(that.vel, that.vel));

    var posVector = Array(2);
    for (var i = 0; i < 2; i++) {
      posVector[i] = that.pos[i] - this.pos[i];
    }

    var posVectorMagnitude = Math.sqrt(dotProd(posVector, posVector));
    var perpVec = Array(2);
    for (var i = 0; i < 2; i++) {
      perpVec[i] = posVector[i] / posVectorMagnitude;
    }

    var ui = dotProd(this.vel, perpVec);
    var vi = dotProd(that.vel, perpVec);

    var mu = this.mass();
    var mv = that.mass();

    var bounceVectoru = [];
    var bounceVectorv = [];
    for (var i = 0; i < 2; i++) {
      var uf = ((2 * mv * vi) + (mu - mv) * ui) / (mu + mv)
      bounceVectoru.push(uf * perpVec[i]);

      var vf = ((2 * mu * ui) + (mv - mu) * vi) / (mu + mv)
      bounceVectorv.push(vf * perpVec[i])
    }

    var newVelu = Array(2);
    var newVelv = Array(2);
    for (var i = 0; i < 2; i++) {
      newVelu[i] = this.vel[i] - (ui * perpVec[i]) + bounceVectoru[i];
      newVelv[i] = that.vel[i] - (vi * perpVec[i]) + bounceVectorv[i];
    }

    this.vel = newVelu;
    that.vel = newVelv;
  };