function ShapeCollection() {
  this._length = 0;
  this._maxLength = 4;
  this.shapes = createSizedArray(this._maxLength);
}

ShapeCollection.prototype.addShape = function (shapeData) {
  if (this._length === this._maxLength) {
    this.shapes = this.shapes.concat(createSizedArray(this._maxLength));
    this._maxLength *= 2;
  }
  this.shapes[this._length] = shapeData;
  this._length += 1;
};

ShapeCollection.prototype.releaseShapes = function () {
  var i;
  for (i = 0; i < this._length; i += 1) {
    shape_pool.release(this.shapes[i]);
  }
  this._length = 0;
};