It is possible to design more variations or permutations of a tile animation than there are tile ids assigned to the source frames. The result of doing so is that portions of the tilesheet become unusable because their tile ids are being used for additional variations of a tile animation.
It would be nice if animations could be assigned “virtual” tile ids that are in addition to the tile ids that correspond physical locations in the tilesheet. So for example, a tilesheet with a 1024x1024px image and 32x32px tiles would be allotted 1024 tile ids for its physical tiles… and an additional X tile ids for however many animations it defines… since we currently have around 256M tile ids available (assuming 4 bits reserved for orientation/mirroring), I wouldn’t be worried about running out of them anytime soon.
I’m not worried about running out of tile IDs, but I am a little worried about making the user interface more complicated. For these additional virtual tiles you’d need some way to add and remove them and they’d need to be displayed differently so that you know they behave differently.
Alternatively, you may be able to include more dummy tiles in your tileset to hook these animations up to.
Another alternative could be to allow multiple named animations per tile, so that you could store more variations that way instead of using many tiles. There is an issue about this already:
I’m currently using dummy tiles… which is fine for us devs, but not quite as intuitive for designers.
Named animations sounds like a neat idea… internally, my engine could assign virtual tile ids of its own and then each tile definition could have a map from animation name to vtid… so that would be a good solution.