code: function localToWorld(x, y, v) {
           // TODO memoization for one set of coords (multitouch)
           v = v || new me.Vector2d();
           v.set(x, y).add(this.pos).sub(me.game.world.pos);
  
           if (!this.currentTransform.isIdentity()) {
             this.currentTransform.multiplyVectorInverse(v);
           }
  
           return v;
         }
docs: convert the given "local" (screen) coordinates into world coordinates
  @name localToWorld
  @memberOf me.Camera2d
  @function
  @param {Number} x
  @param {Number} y
  @param {Number} [v] an optional vector object where to set the
  converted value
  @return {me.Vector2d}