From 743437262ed645204d9040e1705a41902860a648 Mon Sep 17 00:00:00 2001
From: Robert Adams
Date: Wed, 11 Jul 2012 16:07:14 -0700
Subject: Many explanitory comments added to the link and delink code in SOG
 and SOP. Should have no functionality changes.

---
 OpenSim/Region/Framework/Scenes/SceneObjectPart.cs | 28 +++++++++++++++-------
 1 file changed, 20 insertions(+), 8 deletions(-)

(limited to 'OpenSim/Region/Framework/Scenes/SceneObjectPart.cs')

diff --git a/OpenSim/Region/Framework/Scenes/SceneObjectPart.cs b/OpenSim/Region/Framework/Scenes/SceneObjectPart.cs
index b3f11a7..4b2fede 100644
--- a/OpenSim/Region/Framework/Scenes/SceneObjectPart.cs
+++ b/OpenSim/Region/Framework/Scenes/SceneObjectPart.cs
@@ -693,9 +693,11 @@ namespace OpenSim.Region.Framework.Scenes
             {
                 // If this is a linkset, we don't want the physics engine mucking up our group position here.
                 PhysicsActor actor = PhysActor;
+                // If physical and the root prim of a linkset, the position of the group is what physics thinks.
                 if (actor != null && ParentID == 0)
                     m_groupPosition = actor.Position;
 
+                // If I'm an attachment, my position is reported as the position of who I'm attached to
                 if (ParentGroup.IsAttachment)
                 {
                     ScenePresence sp = ParentGroup.Scene.GetScenePresence(ParentGroup.AttachedAvatar);
@@ -721,7 +723,7 @@ namespace OpenSim.Region.Framework.Scenes
                         }
                         else
                         {
-                            // To move the child prim in respect to the group position and rotation we have to calculate
+                            // The physics engine always sees all objects (root or linked) in world coordinates.
                             actor.Position = GetWorldPosition();
                             actor.Orientation = GetWorldRotation();
                         }
@@ -795,6 +797,8 @@ namespace OpenSim.Region.Framework.Scenes
             {
                 // We don't want the physics engine mucking up the rotations in a linkset
                 PhysicsActor actor = PhysActor;
+                // If this is a root of a linkset, the real rotation is what the physics engine thinks.
+                // If not a root prim, the offset rotation is computed by SOG and is relative to the root.
                 if (ParentID == 0 && (Shape.PCode != 9 || Shape.State == 0) && actor != null)
                 {
                     if (actor.Orientation.X != 0f || actor.Orientation.Y != 0f
@@ -1980,14 +1984,20 @@ namespace OpenSim.Region.Framework.Scenes
         /// <returns>A Linked Child Prim objects position in world</returns>
         public Vector3 GetWorldPosition()
         {
-            Quaternion parentRot = ParentGroup.RootPart.RotationOffset;
-            Vector3 axPos = OffsetPosition;
-            axPos *= parentRot;
-            Vector3 translationOffsetPosition = axPos;
-            if(_parentID == 0)
-                return GroupPosition;
+            Vector3 ret;
+            if (_parentID == 0)
+                // if a root SOP, my position is what it is
+                ret = GroupPosition;
             else
-                return ParentGroup.AbsolutePosition + translationOffsetPosition;
+            {
+                // If a child SOP, my position is relative to the root SOP so take
+                //    my info and add the root's position and rotation to
+                //    get my world position.
+                Quaternion parentRot = ParentGroup.RootPart.RotationOffset;
+                Vector3 translationOffsetPosition = OffsetPosition * parentRot;
+                ret = ParentGroup.AbsolutePosition + translationOffsetPosition;
+            }
+            return ret;
         }
 
         /// <summary>
@@ -2004,6 +2014,8 @@ namespace OpenSim.Region.Framework.Scenes
             }
             else
             {
+                // A child SOP's rotation is relative to the root SOP's rotation.
+                // Combine them to get my absolute rotation.
                 Quaternion parentRot = ParentGroup.RootPart.RotationOffset;
                 Quaternion oldRot = RotationOffset;
                 newRot = parentRot * oldRot;
-- 
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