Summary
Allow using collections of simple collision shapes (as defined in the static mesh editor) for collision.
What problem does this solve?
Simplified collision often makes simulation more stable. Unreal has decent support for authoring the simple collisions by composing them from shapes. This feature would let MuJoCo use that collision, rather than trying to do convex decomposition on the mesh itself.
Proposed behaviour
In my prototype, I added a new toggle in MjQuickConvert to use the simple collision mesh, as well as a density modifier (I haven't gave it much thought to have a per-shape density just yet, or perhaps using the complex mesh just for the intertia computations, but keeping the simple collision simply for the collision):
Then I added a few simple collision meshes to a complex static mesh that was not handled well by the convex decomposition:
The compiled XML contained this object definition:
<body name="SM_Mug_142_MjBody" pos="17.6752 -8.03431 0.832553" quat="0.754406 0.111619 -0.133022 -0.633023">
<joint name="SM_Mug_142FreeJoint" type="free"/>
<geom name="Geom_0_visual_1" type="mesh" contype="0" conaffinity="0" group="2" mesh="SM_Mug_01"/>
<geom name="Geom_0_box_0_1" size="0.0331591 0.0334117 0.0523398" pos="-2.14577e-08 0.00281814 0.0523399" type="box" group="3" friction="1 1 1" solref="0.02 0.9" solimp="0.9 1 0.001" density="100"/>
<geom name="Geom_0_box_1" size="0.00540711 0.01582 0.00428518" pos="-2.14577e-08 0.0531776 0.0455254" quat="0.931078 0.364821 0 0" type="box" group="3" friction="1 1 1" solref="0.02 0.9" solimp="0.9 1 0.001" density="100"/>
<geom name="Geom_0_box_2" size="0.00540712 0.01582 0.00428517" pos="-2e-08 0.0643512 0.071028" quat="0.809304 -0.587391 0 0" type="box" group="3" friction="1 1 1" solref="0.02 0.9" solimp="0.9 1 0.001" density="100"/>
<geom name="Geom_0_box_3" size="0.00540712 0.01582 0.00428517" pos="-2e-08 0.0433983 0.0819769" quat="0.999998 -0.00183656 0 0" type="box" group="3" friction="1 1 1" solref="0.02 0.9" solimp="0.9 1 0.001" density="100"/>
<geom name="Geom_0_capsule_0" size="0.0423401 0.00810191" pos="-2.14577e-08 0.00149977 0.0523399" quat="6.08398e-09 1 0 0" type="capsule" group="3" friction="1 1 1" solref="0.02 0.9" solimp="0.9 1 0.001" density="100"/>
</body>API sketch (optional)
In my prototype, the code changes are primarily in the MjQuickConvert component, we just introspect the static mesh and grab its simple collision meshes, and then make sure the generated spec reflects them.
Alternatives considered (optional)
No response
How important is this to you?
Blocks my project
Summary
Allow using collections of simple collision shapes (as defined in the static mesh editor) for collision.
What problem does this solve?
Simplified collision often makes simulation more stable. Unreal has decent support for authoring the simple collisions by composing them from shapes. This feature would let MuJoCo use that collision, rather than trying to do convex decomposition on the mesh itself.
Proposed behaviour
In my prototype, I added a new toggle in
MjQuickConvertto use the simple collision mesh, as well as a density modifier (I haven't gave it much thought to have a per-shape density just yet, or perhaps using the complex mesh just for the intertia computations, but keeping the simple collision simply for the collision):Then I added a few simple collision meshes to a complex static mesh that was not handled well by the convex decomposition:
The compiled XML contained this object definition:
API sketch (optional)
Alternatives considered (optional)
No response
How important is this to you?
Blocks my project