Normalize rotations after solving constraints in solver #345
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Jondolf
added
bugfix
A-Dynamics
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Sorry I didn't get back to this! January was busier than anticipated, and I've had covid for the whole last month. I'll be around again sometime! |
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Objective
Adopted from #237 by @mattdm, fixes #235.
Constraints update rotation by adding or subtracting quaternions. Unlike multiplying unit quaternions (the typical way to "add" together rotations), this can result in rotations becoming unnormalized. This can cause explosions (see #235), and cause panics when trying to rotate Bevy's direction types.
Solution
Normalize the rotations after the constraint rotation delta has been applied. This does come with a small extra cost, but I believe it is worth it for stability. The normalization is also present in some other XPBD implementations I've found, like this one.