1 files changed, 17 insertions, 0 deletions

diff --git a/OpenSim/Region/Environment/Scenes/SceneGraph.cs b/OpenSim/Region/Environment/Scenes/SceneGraph.cs
index dbb8539..d998dbb 100644
--- a/OpenSim/Region/Environment/Scenes/SceneGraph.cs
+++ b/OpenSim/Region/Environment/Scenes/SceneGraph.cs
@@ -159,6 +159,22 @@ namespace OpenSim.Region.Environment.Scenes
         {
             lock (m_syncRoot)
             {
+                // Here is where the Scene calls the PhysicsScene. This is a one-way
+                // interaction; the PhysicsScene cannot access the calling Scene directly.
+                // But with joints, we want a PhysicsActor to be able to influence a
+                // non-physics SceneObjectPart. In particular, a PhysicsActor that is connected
+                // with a joint should be able to move the SceneObjectPart which is the visual
+                // representation of that joint (for editing and serialization purposes).
+                // However the PhysicsActor normally cannot directly influence anything outside
+                // of the PhysicsScene, and the non-physical SceneObjectPart which represents
+                // the joint in the Scene does not exist in the PhysicsScene.
+                //
+                // To solve this, we have an event in the PhysicsScene that is fired when a joint
+                // has changed position (because one of its associated PhysicsActors has changed 
+                // position).
+                //
+                // Therefore, JointMoved and JointDeactivated events will be fired as a result of the following Simulate().
+
                 return _PhyScene.Simulate((float)elapsed);
             }
         }
@@ -875,6 +891,7 @@ namespace OpenSim.Region.Environment.Scenes
         {
             List<EntityBase> EntityList = GetEntities();
 
+            // FIXME: use a dictionary here
             foreach (EntityBase ent in EntityList)
             {
                 if (ent is SceneObjectGroup)