Added section on collision filtering and updated APIChanges.md

Docs/APIChanges.md

@@ -6,6 +6,7 @@ Changes that make some state saved through SaveBinaryState from a prior version
 
 ## Changes between v2.0.1 and latest
 
+* 20221231 - ObjectLayerPairFilter and ObjectVsBroadPhaseLayerFilter are now objects instead of function pointers. (4315ad53e354f094f753664fcf7a52870f6915e4)
 * 20221208 - ContactListener::OnContactValidate is reporting collisions relative to inBaseOffset. Add this to the contact point if you want world space positions. (428611482825e369e60e0a5daf17c69a4d0f2a6f)
 * 20221204 - Changes related to double precision support for positions (a2c1c22059fa031faf0208258e654bcff79a63e4)
 	* In many places in the public API Vec3 has been replaced by RVec3 (a Vec3 of Real values which can either be double or float depending on if JPH_DOUBLE_PRECISION is defined). In the same way RMat44 replaces Mat44. When compiling in single precision mode (the default) you should not notice a change.

Docs/Architecture.md

@@ -254,7 +254,7 @@ Constraints can be turned on / off by calling Constraint::SetEnabled. After ever
 
 When bodies are added to the PhysicsSystem, they are inserted in the broad phase ([BroadPhaseQuadTree](@ref BroadPhaseQuadTree)). This provides quick coarse collision detection based on the axis aligned bounding box (AABB) of a body.
 
-The broad phase is divided in layers, each layer has a AABB quad tree associated with it. When constructing the physics system a [ObjectLayerPairFilter](@ref ObjectLayerPairFilter) needs to be provided which determines which object layers collide with which other layer. If two layers don't collide, the objects inside those layers cannot collide. A standard setup would be to have a MOVING and a NON_MOVING layer, where NON_MOVING doesn't collide with NON_MOVING and all other permutations collide. This ensures that all static bodies are in one tree (which is infrequently updated) and all dynamic bodies are in another (which is updated every simulation step). It is possible to create more layers like a BULLET layer for high detail collision bodies that are attached to lower detail simulation bodies, the MOVING layer would not collide with the BULLET layer, but when performing e.g. weapon collision queries you can filter for only objects in the BULLET layer.
+The broad phase is divided in layers, each layer has a AABB quad tree associated with it. When constructing the physics system an [ObjectVsBroadPhaseLayerFilter](@ref ObjectVsBroadPhaseLayerFilter) and [ObjectLayerPairFilter](@ref ObjectLayerPairFilter) need to be provided. These determine which object layers collide with which other layer. If two layers don't collide, the objects inside those layers cannot collide. A standard setup would be to have a MOVING and a NON_MOVING layer, where NON_MOVING doesn't collide with NON_MOVING and all other permutations collide. This ensures that all static bodies are in one tree (which is infrequently updated) and all dynamic bodies are in another (which is updated every simulation step). It is possible to create more layers like a BULLET layer for high detail collision bodies that are attached to lower detail simulation bodies, the MOVING layer would not collide with the BULLET layer, but when performing e.g. weapon collision queries you can filter for only objects in the BULLET layer.
 
 Since we want to access bodies concurrently the broad phase has special behavior. When a body moves, all nodes in the AABB tree from root to the node where the body resides will be expanded using a lock-free approach. This way multiple threads can move bodies at the same time without requiring a lock on the broad phase. Nodes that have been expanded are marked and during the next physics step a new tight-fitting tree will be built in the background while the physics step is running. This new tree will replace the old tree before the end of the simulation step. This is possible since no bodies can be added/removed during the physics step.
 
@@ -268,6 +268,18 @@ For very long running jobs (e.g. navigation mesh creation) it is possible to que
 
 The narrow phase queries are all handled through the [GJK](@ref GJKClosestPoint) and [EPA](@ref EPAPenetrationDepth) algorithms.
 
+## Collision filtering
+
+As touched upon in the Broad Phase section, there are various collision filtering functions:
+
+* Broadphase layer: Each broad phase layer will result in it's own quad tree so you should not have too many of them. See the Broad Phase section for examples. See [ObjectVsBroadPhaseLayerFilter](@ref ObjectVsBroadPhaseLayerFilter).
+* Object layer: An object layer maps to one or more broadphase layers to test against, this allows you to very quickly discard large amounts of bodies. See [ObjectLayerPairFilter](@ref ObjectLayerPairFilter) (used for simulation) and [ObjectLayerFilter](@ref ObjectLayerFilter) (used for collision queries).
+* Group filter: Most expensive filtering (bounding boxes already overlap), used only during simulation. Allows you fine tune collision e.g. by discarding collisions between bodies connected by a constraint. See [GroupFilter](@ref GroupFilter) and implementation for ragdolls [GroupFilterTable](@ref GroupFilterTable).
+* Body filter: This filter is used instead of the group filter if you do collision queries like CastRay. See [BodyFilter](@ref BodyFilter).
+* Shape filter: This filter is used only during collision queries and can be used to filter out individual (sub)shapes. See [ShapeFilter](@ref ShapeFilter).
+
+The filter functions are listed in the order they're called. To avoid work, try to filter out collisions as early as possible.
+
 ## The Simulation Step
 
 The simulation step [PhysicsSystem::Update](@ref PhysicsSystem::Update) uses jobs ([JobSystem](@ref JobSystem)) to perform the needed work. This allows spreading the workload across multiple CPU's. We use a Sequential Impulse solver with warm starting as described in [Modeling and Solving Constraints - Erin Catto](https://box2d.org/files/ErinCatto_ModelingAndSolvingConstraints_GDC2009.pdf)