Broken Shrinkwrap Modifier (and Bendy Bones) #73840
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Reference: blender/blender#73840
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System Information
Operating system: Windows 10 1909
Graphics card: Nvidia GeForce RTX 2070
Blender Version
Broken: 2.82, 2020-2-16
Worked: 2.81-adfe68e2025b-windows64
d1657b406e
Short description of error
The shrinkwrap modifier seems to have a completely different algorithm in this new version of Blender. The eyebrows, which I projected onto her face, worked perfect in 2.81, but is completely distorted in 2.82
2.81 on top, 2.82 on the bottom.
{F8341304}
File
clothes.blend
EDIT Upon closer inspection, it's a problem of both shrinkwrap AND bendy bones. For some reason, the roll of the bendy bones are really messed up.
Added subscriber: @sagaevan
Broken Shrinkwrap Modifierto Broken Shrinkwrap Modifier (and Bendy Bones)Added subscriber: @CodyWinchester
I have been looking into this and it seems this has nothing to do with the shrinkwrap modifier. It is the result of changes to the bbone roll calculation.
I have isolated the issue to the changes made in this patch https://developer.blender.org/rBd1657b406ed0f3df9e1690cd445702c6178ffd15
If I reverse the patch the provided file works as it did in 2.81a.
Also, the provided file has the bones using Absolute custom handles and the Start custom handle bone has its head at the same coord as the bbones head which causes roll issues.
Changed status from 'Needs Triage' to: 'Confirmed'
Aaah! Sorry, I guess I just didn't understand bendy bones. Thank you so much!
Added subscribers: @angavrilov, @mont29
@angavrilov can you please check whether that behavior is expected/correct in current code? Or whether
d1657b406
did introduce some regression? Thanks.Absolute handle with position that is the same as the bbone makes no sense. It's like expecting a reasonable result from dividing 0 by 0.
Added subscriber: @dr.sybren
I think
d1657b406
is a considerable improvement. I did some tests, and the old code did produce some dubious results. For example, in a case like this:I would expect the roll to be zero, as the matrix performs no rotation at all. This is also the result now, but before
d1657b406e
it produced a roll of approximately -15 degrees. Another test case:Here the rotation matrix rotates 1.234 radians around the X-axis. Given that an input vector of
(1, 0, 0)
results in a roll of the full 1.234 radians, and an input vector(0, 1, 0)
results in a zero roll, I would expect the answer for the in-between vector(1, 1, 0)
to be in between these values as well. Neither the new code nor the old one produces exactly half the angle, but the new code is certainly closer, with respectively 1.111 and 0.572 radians.To elaborate on this a bit more, the Custom Handles section in the Blender manual states about absolute handles:
This means that there should be a positional difference between the bone positions, or the direction of the Bézier curve is undefined.
Since
d1657b406e
, Blender behaves differently in this undefined case, but I think that's not really a bug.For a more practical answer, if you want handle controls that are located at the head/tail of the bbone, you probably want to use the Tangent mode. Absolute is just the default 'connected chain' mode that allows manually selecting the adjacent bone of the chain, instead of automatically using parent/child.
Changed status from 'Confirmed' to: 'Needs User Info'
@sagaevan I did a quick test with the left eyebrow, and the rig works a lot better with @angavrilov 's suggestion of setting the handle type to Tangent. It does require a flip ({key Alt+F} in edit mode) of the eyebrow control.L bone to work properly, though. Is this a solution you could work with?
Changed status from 'Needs User Info' to: 'Resolved'
I have clarified the requirement (that there should be a distance between the bones) in the manual, see rBM6742.
I'll assume that the silence implies that this issue is indeed solved. If this is not the case, please open a new report with more detail about the issue.