[HyperelasticForcefield] : Breaking bug that prevent MechanicalObject fields modifications when running in batch mode.

[AlbanOdot]

I just encountered a bug that has been replicated on multiple computers when running the given script using python launcher
In the script, the position is modified on the onAnimatedBeginEvent function call.
We can see two behaviors.

By running :

• python3 SofaBugCaribou.py

  • You can observe from the print that the mechanical object positions are not updated at all.
  • Mechanical values such as residual are not impacted either, so, it's not only a python/display bug.
  • It doesn't work either using with self.MO.position.writeable() as pos:

• python3 SofaBugCaribou.py gui

  • The positions are properly modified

Commenting/uncommenting the material/constitutive law reveals that it's the HyperelasticForcefield that causes the problem.

This minimal scene replicates the bug:
BugCaribou.zip

[AlbanOdot]

So far I've tried to remove the draw function from CaribouForcefield (since it interacts with the gui) but it doesn't affect the result.

[jnbrunet]

Étrange... The only reference to the MO position vector in these codes are const read only, so it should not affect anything...

I will try to have a closer look. Let me know if you find other hints.

[AlbanOdot]

For anyone having the same issue, a quick fix has been provided at Sofa issues.