TCastleTransformReference to reference another
TCastleTransform within the same viewport. This is an efficient way to use the same
TCastleTransform multiple times, which is great for memory and speed. Consider using this when you need a lot of copies of something, e.g. lots of trees or grass patches.
TCastleTransformReference instances share the same state with the original, e.g. they will play the same animation. In practice, you will probably most often use this with static (not animated) models.