Question about the removal of convexhull

[abhihjoshi]

Intro

Hi!

I am a first year graduate student, and I use MuJoCo for my research on robot learning.

My setup

MuJoCo v3.2.6
Ubuntu 22.04

My question

I was curious about the reasoning behind removing the convexhull option to disable convex hull generation and any information on this. Are convex hulls now generated for all meshes automatically in newer version? What should be done if we manually provide a convex decomposition of our geoms and do not want to get a new convex hull? Please correct me if I am misunderstanding something here.

Thanks!

Minimal model and/or code that explain my question

No response

Confirmations

• I searched the latest documentation thoroughly before posting.
• I searched previous Issues and Discussions, I am certain this has not been raised before.

[Balint-H]

Hello,

if you add your decomposed meshes as separate mesh geoms to the same body, then each geom will get a hull separately. You have a correct approach, this is one of the approaches you can use to represent concave models.

As far as the removal of the option, the old documentation said:

The only reason to disable this feature is to speed up re-loading of a model with large meshes during model editing (since the convex hull computation is the slowest operation performed by the compiler). However once model design is finished, this feature should be enabled, because the availability of convex hulls substantially speeds up collision detection with large meshes.

In the same update as when convexhull was dropped, mjSpec was introduced. I expect through mjSpec model reloading can be more efficient without needing to reload unchanged assets, making even the one edge case where one would have used convexhull obsolete.

I do also see that the current XML documentation still references the convexhull option in a couple spots, which should be fixed at some point

[abhihjoshi]

Thanks, @Balint-H!