From 013268c28328cc1ff5fce6be82d4b5a0fe14200f Mon Sep 17 00:00:00 2001
From: Taylor Howell <taylorhowell@google.com>
Date: Mon, 12 Jan 2026 08:46:35 -0800
Subject: [PATCH] Documentation: Pair-wise colliders.

PiperOrigin-RevId: 855245724
Change-Id: Iffad5dc426350040f730dc1a7b9766f079ef949e
---
 doc/computation/index.rst   | 138 ++++++++++++++++++++++++++++++++++++
 doc/css/theme_overrides.css |   7 +-
 2 files changed, 144 insertions(+), 1 deletion(-)

diff --git a/doc/computation/index.rst b/doc/computation/index.rst
index 3cbb8738..0f069845 100644
--- a/doc/computation/index.rst
+++ b/doc/computation/index.rst
@@ -1574,6 +1574,144 @@ callbacks. This can be used to incorporate a general-purpose "triangle soup" col
 do not recommend such an approach. Pre-processing the geometry and representing it as a union of convex geoms takes some
 work, but it pays off at runtime and yields both faster and more stable simulation.
 
+.. _coPairwise:
+
+Pair-wise colliders
+^^^^^^^^^^^^^^^^^^^
+
+The table below provides information about the colliders used for different geom pairs. The second row in each cell
+lists the maximum number of contacts generated, possibly with ``multiccd`` enabled. For example, ``Mesh`` / ``Mesh``
+will generate up to 1 contact or with ``multiccd`` up to 4 contacts.
+
+.. list-table::
+   :header-rows: 1
+   :stub-columns: 1
+   :widths: auto
+   :class: table-pairwise
+
+   * -
+     - Sphere
+     - Capsule
+     - Ellipsoid
+     - Cylinder
+     - Box
+     - Mesh
+     - SDF
+   * - Plane
+     - | primitive
+       | **1**
+     - | primitive
+       | **2**
+     - | primitive
+       | **1**
+     - | primitive
+       | **2**
+     - | primitive
+       | **4**
+     - | primitive
+       | **3**
+     - | primitive
+       | **1**
+   * - HField
+     - | HFieldCCD
+       | :ref:`mjMAXCONPAIR <glNumeric>`
+     - | HFieldCCD
+       | :ref:`mjMAXCONPAIR <glNumeric>`
+     - | HFieldCCD
+       | :ref:`mjMAXCONPAIR <glNumeric>`
+     - | HFieldCCD
+       | :ref:`mjMAXCONPAIR <glNumeric>`
+     - | HFieldCCD
+       | :ref:`mjMAXCONPAIR <glNumeric>`
+     - | HFieldCCD
+       | :ref:`mjMAXCONPAIR <glNumeric>`
+     - | HFieldSDF
+       | :ref:`sdf_initpoints <option-sdf_initpoints>`
+   * - Sphere
+     - | primitive
+       | **1**
+     - | primitive
+       | **1**
+     - | CCD
+       | **1**
+     - | primitive
+       | **1**
+     - | primitive
+       | **1**
+     - | CCD
+       | **1**
+     - | SDF
+       | :ref:`sdf_initpoints <option-sdf_initpoints>`
+   * - Capsule
+     -
+     - | primitive
+       | **2**
+     - | CCD
+       | **1**
+     - | CCD
+       | **1**, **4**
+     - | primitive
+       | **2**
+     - | CCD
+       | **1**, **4**
+     - | SDF
+       | :ref:`sdf_initpoints <option-sdf_initpoints>`
+   * - Ellipsoid
+     -
+     -
+     - | CCD
+       | **1**
+     - | CCD
+       | **1**
+     - | CCD
+       | **1**
+     - | CCD
+       | **1**
+     - | SDF
+       | :ref:`sdf_initpoints <option-sdf_initpoints>`
+   * - Cylinder
+     -
+     -
+     -
+     - | CCD
+       | **1**, **4**
+     - | CCD
+       | **1**, **4**
+     - | CCD
+       | **1**, **4**
+     - | SDF
+       | :ref:`sdf_initpoints <option-sdf_initpoints>`
+   * - Box
+     -
+     -
+     -
+     -
+     - | primitive
+       | **8**
+     - | CCD
+       | **1**, **4**
+     - | SDF
+       | :ref:`sdf_initpoints <option-sdf_initpoints>`
+   * - Mesh
+     -
+     -
+     -
+     -
+     -
+     - | CCD
+       | **1**, **4**
+     - | MeshSDF
+       | :ref:`sdf_initpoints <option-sdf_initpoints>`
+   * - SDF
+     -
+     -
+     -
+     -
+     -
+     -
+     - | SDF
+       | :ref:`sdf_initpoints <option-sdf_initpoints>`
+
 .. _Sleeping:
 
 Sleeping islands
diff --git a/doc/css/theme_overrides.css b/doc/css/theme_overrides.css
index 6df21b1a..45f94131 100644
--- a/doc/css/theme_overrides.css
+++ b/doc/css/theme_overrides.css
@@ -50,7 +50,12 @@ body[data-theme="dark"] table.docutils:not(.mjcf-attributes) {
   font-size: 93%;
 }
 
-.small-centered td, .small-centered th {
+.table-pairwise {
+  font-size: 85%;
+}
+
+.small-centered td, .small-centered th,
+.table-pairwise td, .table-pairwise th {
   text-align: center !important;
   vertical-align: middle !important;
   border: 2px solid var(--color-table-border) !important;