Centering joints

[ZhengyiLuo]

Centering the joints before applying to user-supplied translation.

Reference issue: #8 (comment)

Thank you so much!

[PerryXDeng]

This seems to be a rather important change that can prevent unexpected bugs
👍. Since the centering condition does not depend on the existence of translation, it looks like they can be taken out of the larger if-else block entirely

[PerryXDeng]

Seems like this if block (and the one above in line 147-150) is independent of the surrounding clauses.

[hassony2]

Hi @ZhengyiLuo,

Thank you for pointing out this behavior !
Indeed, currently centering is done only if translation is 0 or none, which might not be the intuitive behavior.

However, accepting such a pull request can cause unexpected changes for people who are unknowingly using the current code, e.g. who have set a center_idx which is not used because they have provided a translation (th_trans)
If they upgrade with the added pull request suddenly their translations won't be the same anymore, and existing code might break.

I think a solution at this point would be the following:
Highlight the current behavior in the documentation (something like "Note that providing a translation with prevent the centering on a joint in the forward pass, so center_idx will be ignored if th_trans is provided")

What do you think?

If both centering and translation is needed for your specific use-case, maybe a solution could be to manually apply the translation on the returned joint and vertex values from the layer ?

Cheers !