localToWorld(x, y, v) {
		// TODO memoization for one set of coords (multitouch)
		v = v || vector2dPool.get();
		v.set(x, y).add(this.pos).sub(game.world.pos);
		if (!this.currentTransform.isIdentity()) {
			this.invCurrentTransform.apply(v);
		}
		return v;
	}
convert the given "local" (screen) coordinates into world coordinates
@param {number} x - the x coordinate of the local point to be converted
@param {number} y - the y coordinate of the local point to be converted
@param {Vector2d} [v] - an optional vector object where to set the converted value
@returns {Vector2d}