void update(double deltaTime, SetEntity entities) {
  for (var i = 0; i < entities.size; i++) {
    Entity entity = entities[i];
    TransformComponent transform = transformComponents[entity];
    VelocityComponent rotation = velocityComponents[entity];
    transform.rotation += rotation.velocity * deltaTime;
    transform.dirty = true;
  }
}

void updateSprite(TransformComponent transform, SpriteComponent sprite) {
  var textureRegion = sprite.textureRegion;
  if (transform.dirty && textureRegion != null) {
    var scos = cos(transform.rotation) * transform.scale;
    var ssin = sin(transform.rotation) * transform.scale;
    var tx = -scos * textureRegion.anchorX + ssin * textureRegion.anchorY;
    var ty = -ssin * textureRegion.anchorX - scos * textureRegion.anchorY;
    sprite.transformData.set(scos, ssin, tx, ty);
    transform.dirty = false;
  }
}