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Update multiccd documentation.

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PiperOrigin-RevId: 902779253
Change-Id: I767cd0a230b78efe2a71f83e5f2f134268997dcb
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Kyle Bayes
2026-04-20 12:52:30 -07:00
committed by Copybara-Service
parent 6cb6e5a93f
commit bc5883e82f
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doc/computation/index.rst
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@@ -1656,23 +1656,25 @@ Both pipelines are controlled by a tolerance (in units of distance) and maximum
Multiple contacts
^^^^^^^^^^^^^^^^^
Some colliders can return more than one contact per colliding pair to model line or surface contacts, as when two flat
Some colliders can return more than one contact per colliding pair to model edge or surface contacts, as when two flat
objects touch. For example the capsule-plane and box-plane colliders can return up to two or four contacts,
respectively. Standard general-purpose convex collision algorithms like MPR and GJK always return a single contact
respectively. Standard general-purpose convex collision algorithms like MPR and GJK/EPA always return a single contact
point, which is problematic for surface contact scenarios (e.g., box-stacking). Both of MuJoCo's CCD pipelines can
return multiple points per contacting pair ("multiccd"). This behavior is controlled by the
:ref:`multiccd<option-flag-multiccd>` flag, but is implemented in different ways with different trade-offs:
libccd pipeline (legacy)
multi-run pipeline (legacy)
Multiple contact points are found by rotating the two geoms by ±1e-3 radians around the tangential axes and
re-running the collision routine. If a new contact is detected it is added, allowing for up to 4 additional contact
points. This method is effective, but increases the cost of each collision call by a factor of 5.
points. This method is effective, but increases the cost of each collision call by a factor of 5. This method is
used when the :ref:`nativeccd<option-flag-nativeccd>` flag is disabled, and for geoms collisions involving cylinders
and capsules or with :ref:`positive contact margins<body-geom-margin>`.
native pipeline
Native multiccd discovers multiple contacts using a novel analysis of the contacting surfaces at the solution,
avoiding full re-runs of the collision routine, and is thus effectively "free". Note that native multiccd currently
does not support positive contact margins. If one of the two geoms has a positive margin, native multiccd will fall
back to legacy algorithm.
single-shot pipeline
The single-shot pipeline is used in conjunction with the native CCD pipeline, i.e., when the
:ref:`nativeccd<option-flag-nativeccd>` flag is enabled. As this pipeline is one-shot and most of the geom analysis
is done at compilation time, there is very little performance overhead. Supported geoms are boxes and meshes without
:ref:`positive contact margins<body-geom-margin>`.
.. _coDistance: