BulletSim: Fix crash on the destruction of physical linksets.

While fixing the above, add methods to physical body and shape pointer
wrapper so routines won't have to know that IntPtr.Zero means no
physical instance.
Fix problem with physical linksets failing after a few sits and
unsits by properly restoring child prom positions for compound
linksets after multiple selection and deselections.

12 files changed, 155 insertions, 38 deletions

diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSCharacter.cs b/OpenSim/Region/Physics/BulletSPlugin/BSCharacter.cs
index 21aa9be..88460cc 100644
--- a/OpenSim/Region/Physics/BulletSPlugin/BSCharacter.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSCharacter.cs
@@ -124,7 +124,9 @@ public sealed class BSCharacter : BSPhysObject
         PhysicsScene.TaintedObject("BSCharacter.destroy", delegate()
         {
             PhysicsScene.Shapes.DereferenceBody(PhysBody, true, null);
+            PhysBody.Clear();
             PhysicsScene.Shapes.DereferenceShape(PhysShape, true, null);
+            PhysShape.Clear();
         });
     }
 
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSConstraint.cs b/OpenSim/Region/Physics/BulletSPlugin/BSConstraint.cs
index 65fac00..6b1e304 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSConstraint.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSConstraint.cs
@@ -57,7 +57,7 @@ public abstract class BSConstraint : IDisposable
         if (m_enabled)
         {
             m_enabled = false;
-            if (m_constraint.ptr != IntPtr.Zero)
+            if (m_constraint.HasPhysicalConstraint)
             {
                 bool success = BulletSimAPI.DestroyConstraint2(m_world.ptr, m_constraint.ptr);
                 m_world.physicsScene.DetailLog("{0},BSConstraint.Dispose,taint,id1={1},body1={2},id2={3},body2={4},success={5}",
@@ -65,7 +65,7 @@ public abstract class BSConstraint : IDisposable
                                     m_body1.ID, m_body1.ptr.ToString("X"),
                                     m_body2.ID, m_body2.ptr.ToString("X"),
                                     success);
-                m_constraint.ptr = System.IntPtr.Zero;
+                m_constraint.Clear();
             }
         }
     }
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSConstraint6Dof.cs b/OpenSim/Region/Physics/BulletSPlugin/BSConstraint6Dof.cs
index 23ef052..b073555 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSConstraint6Dof.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSConstraint6Dof.cs
@@ -65,7 +65,7 @@ public sealed class BSConstraint6Dof : BSConstraint
         m_world = world;
         m_body1 = obj1;
         m_body2 = obj2;
-        if (obj1.ptr == IntPtr.Zero || obj2.ptr == IntPtr.Zero)
+        if (!obj1.HasPhysicalBody || !obj2.HasPhysicalBody)
         {
             world.physicsScene.DetailLog("{0},BS6DOFConstraint,badBodyPtr,wID={1}, rID={2}, rBody={3}, cID={4}, cBody={5}",
                             BSScene.DetailLogZero, world.worldID,
@@ -83,7 +83,7 @@ public sealed class BSConstraint6Dof : BSConstraint
             world.physicsScene.DetailLog("{0},BS6DofConstraint,createMidPoint,wID={1}, csrt={2}, rID={3}, rBody={4}, cID={5}, cBody={6}",
                                 BSScene.DetailLogZero, world.worldID, m_constraint.ptr.ToString("X"),
                                 obj1.ID, obj1.ptr.ToString("X"), obj2.ID, obj2.ptr.ToString("X"));
-            if (m_constraint.ptr == IntPtr.Zero)
+            if (!m_constraint.HasPhysicalConstraint)
             {
                 world.physicsScene.Logger.ErrorFormat("{0} Failed creation of 6Dof constraint. rootID={1}, childID={2}",
                                 LogHeader, obj1.ID, obj2.ID);
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSLinkset.cs b/OpenSim/Region/Physics/BulletSPlugin/BSLinkset.cs
index 0df4310..777c5cb 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSLinkset.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSLinkset.cs
@@ -32,6 +32,14 @@ using OMV = OpenMetaverse;
 
 namespace OpenSim.Region.Physics.BulletSPlugin
 {
+
+// A BSPrim can get individual information about its linkedness attached
+//    to it through an instance of a subclass of LinksetInfo.
+// Each type of linkset will define the information needed for its type.
+public abstract class BSLinksetInfo
+{
+}
+
 public abstract class BSLinkset
 {
     // private static string LogHeader = "[BULLETSIM LINKSET]";
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSLinksetCompound.cs b/OpenSim/Region/Physics/BulletSPlugin/BSLinksetCompound.cs
index bc9f9be..fe5b5e3 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSLinksetCompound.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSLinksetCompound.cs
@@ -32,6 +32,31 @@ using OMV = OpenMetaverse;
 
 namespace OpenSim.Region.Physics.BulletSPlugin
 {
+
+// When a child is linked, the relationship position of the child to the parent
+//    is remembered so the child's world position can be recomputed when it is
+//    removed from the linkset.
+sealed class BSLinksetCompoundInfo : BSLinksetInfo
+{
+    public OMV.Vector3 OffsetPos;
+    public OMV.Quaternion OffsetRot;
+    public BSLinksetCompoundInfo(OMV.Vector3 p, OMV.Quaternion r)
+    {
+        OffsetPos = p;
+        OffsetRot = r;
+    }
+    public override string ToString()
+    {
+        StringBuilder buff = new StringBuilder();
+        buff.Append("<p=");
+        buff.Append(OffsetPos.ToString());
+        buff.Append(",r=");
+        buff.Append(OffsetRot.ToString());
+        buff.Append(">");
+        return buff.ToString();
+    }
+};
+
 public sealed class BSLinksetCompound : BSLinkset
 {
     private static string LogHeader = "[BULLETSIM LINKSET COMPOUND]";
@@ -44,6 +69,7 @@ public sealed class BSLinksetCompound : BSLinkset
     // For compound implimented linksets, if there are children, use compound shape for the root.
     public override BSPhysicsShapeType PreferredPhysicalShape(BSPhysObject requestor)
     { 
+        // Returning 'unknown' means we don't have a preference.
         BSPhysicsShapeType ret = BSPhysicsShapeType.SHAPE_UNKNOWN;
         if (IsRoot(requestor) && HasAnyChildren)
         {
@@ -63,10 +89,10 @@ public sealed class BSLinksetCompound : BSLinkset
         // InternalRefresh(requestor);
     }
 
+    // Schedule a refresh to happen after all the other taint processing.
     private void InternalRefresh(BSPhysObject requestor)
     {
         DetailLog("{0},BSLinksetCompound.Refresh,schedulingRefresh,requestor={1}", LinksetRoot.LocalID, requestor.LocalID);
-        // Queue to happen after all the other taint processing
         PhysicsScene.PostTaintObject("BSLinksetCompound.Refresh", requestor.LocalID, delegate()
         {
             if (IsRoot(requestor) && HasAnyChildren)
@@ -108,7 +134,7 @@ public sealed class BSLinksetCompound : BSLinkset
         {
             // The non-physical children can come back to life.
             BulletSimAPI.RemoveFromCollisionFlags2(child.PhysBody.ptr, CollisionFlags.CF_NO_CONTACT_RESPONSE);
-            // Don't force activation so setting of DISABLE_SIMULATION can stay.
+            // Don't force activation so setting of DISABLE_SIMULATION can stay if used.
             BulletSimAPI.Activate2(child.PhysBody.ptr, false);
             ret = true;
         }
@@ -146,6 +172,10 @@ public sealed class BSLinksetCompound : BSLinkset
 
         if (!IsRoot(child))
         {
+            // Because it is a convenient time, recompute child world position and rotation based on
+            //    its position in the linkset.
+            RecomputeChildWorldPosition(child, true);
+
             // Cause the current shape to be freed and the new one to be built.
             InternalRefresh(LinksetRoot);
             ret = true;
@@ -154,6 +184,42 @@ public sealed class BSLinksetCompound : BSLinkset
         return ret;
     }
 
+    // When the linkset is built, the child shape is added
+    //    to the compound shape relative to the root shape. The linkset then moves around but
+    //    this does not move the actual child prim. The child prim's location must be recomputed
+    //    based on the location of the root shape.
+    private void RecomputeChildWorldPosition(BSPhysObject child, bool inTaintTime)
+    {
+        BSLinksetCompoundInfo lci = child.LinksetInfo as BSLinksetCompoundInfo;
+        if (lci != null)
+        {
+            if (inTaintTime)
+            {
+                OMV.Vector3 oldPos = child.RawPosition;
+                child.ForcePosition = LinksetRoot.RawPosition + lci.OffsetPos;
+                child.ForceOrientation = LinksetRoot.RawOrientation * lci.OffsetRot;
+                DetailLog("{0},BSLinksetCompound.RecomputeChildWorldPosition,oldPos={1},lci={2},newPos={3}",
+                                            child.LocalID, oldPos, lci, child.RawPosition);
+            }
+            else
+            {
+                // TaintedObject is not used here so the raw position is set now and not at taint-time.
+                child.Position = LinksetRoot.RawPosition + lci.OffsetPos;
+                child.Orientation = LinksetRoot.RawOrientation * lci.OffsetRot;
+            }
+        }
+        else
+        {
+            // This happens when children have been added to the linkset but the linkset
+            //     has not been constructed yet. So like, at taint time, adding children to a linkset
+            //     and then changing properties of the children (makePhysical, for instance)
+            //     but the post-print action of actually rebuilding the linkset has not yet happened.
+            // PhysicsScene.Logger.WarnFormat("{0} Restoring linkset child position failed because of no relative position computed. ID={1}",
+            //                                 LogHeader, child.LocalID);
+            DetailLog("{0},BSLinksetCompound.recomputeChildWorldPosition,noRelativePositonInfo", child.LocalID);
+        }
+    }
+
     // Companion to RemoveBodyDependencies(). If RemoveBodyDependencies() returns 'true',
     // this routine will restore the removed constraints.
     // Called at taint-time!!
@@ -192,8 +258,7 @@ public sealed class BSLinksetCompound : BSLinkset
                             child.LocalID, child.PhysBody.ptr.ToString("X"));
 
             // Cause the child's body to be rebuilt and thus restored to normal operation
-            // TODO: position and rotation must be restored because the child could have moved
-            //    based on the linkset.
+            RecomputeChildWorldPosition(child, false);
             child.ForceBodyShapeRebuild(false);
 
             if (!HasAnyChildren)
@@ -228,43 +293,57 @@ public sealed class BSLinksetCompound : BSLinkset
         {
             if (!IsRoot(cPrim))
             {
-                // Each child position and rotation is given relative to the root.
-                OMV.Quaternion invRootOrientation = OMV.Quaternion.Inverse(LinksetRoot.RawOrientation);
-                OMV.Vector3 displacementPos = (cPrim.RawPosition - LinksetRoot.RawPosition) * invRootOrientation;
-                OMV.Quaternion displacementRot = cPrim.RawOrientation * invRootOrientation;
+                // Compute the displacement of the child from the root of the linkset.
+                // This info is saved in the child prim so the relationship does not
+                //    change over time and the new child position can be computed
+                //    when the linkset is being disassembled (the linkset may have moved).
+                BSLinksetCompoundInfo lci = cPrim.LinksetInfo as BSLinksetCompoundInfo;
+                if (lci == null)
+                {
+                    // Each child position and rotation is given relative to the root.
+                    OMV.Quaternion invRootOrientation = OMV.Quaternion.Inverse(LinksetRoot.RawOrientation);
+                    OMV.Vector3 displacementPos = (cPrim.RawPosition - LinksetRoot.RawPosition) * invRootOrientation;
+                    OMV.Quaternion displacementRot = cPrim.RawOrientation * invRootOrientation;
+
+                    // Save relative position for recomputing child's world position after moving linkset.
+                    lci = new BSLinksetCompoundInfo(displacementPos, displacementRot);
+                    cPrim.LinksetInfo = lci;
+                    DetailLog("{0},BSLinksetCompound.RecomputeLinksetCompound,creatingRelPos,lci={1}", cPrim.LocalID, lci);
+                }
 
                 DetailLog("{0},BSLinksetCompound.RecomputeLinksetCompound,addMemberToShape,mID={1},mShape={2},dispPos={3},dispRot={4}",
-                    LinksetRoot.LocalID, cPrim.LocalID, cPrim.PhysShape, displacementPos, displacementRot);
+                    LinksetRoot.LocalID, cPrim.LocalID, cPrim.PhysShape, lci.OffsetPos, lci.OffsetRot);
 
                 if (cPrim.PhysShape.isNativeShape)
                 {
-                    // A native shape is turning into a null collision shape because native
+                    // A native shape is turning into a hull collision shape because native
                     //    shapes are not shared so we have to hullify it so it will be tracked
                     //    and freed at the correct time. This also solves the scaling problem
                     //    (native shapes scaled but hull/meshes are assumed to not be).
+                    // TODO: decide of the native shape can just be used in the compound shape.
+                    //    Use call to CreateGeomNonSpecial().
                     BulletShape saveShape = cPrim.PhysShape;
-                    cPrim.PhysShape.ptr = IntPtr.Zero;  // Don't let the create free the child's shape
+                    cPrim.PhysShape.Clear();        // Don't let the create free the child's shape
+                    // PhysicsScene.Shapes.CreateGeomNonSpecial(true, cPrim, null);
                     PhysicsScene.Shapes.CreateGeomMeshOrHull(cPrim, null);
                     BulletShape newShape = cPrim.PhysShape;
                     cPrim.PhysShape = saveShape;
-                    BulletSimAPI.AddChildShapeToCompoundShape2(LinksetRoot.PhysShape.ptr, newShape.ptr, displacementPos, displacementRot);
+                    BulletSimAPI.AddChildShapeToCompoundShape2(LinksetRoot.PhysShape.ptr, newShape.ptr, lci.OffsetPos , lci.OffsetRot);
                 }
                 else
                 {
                     // For the shared shapes (meshes and hulls), just use the shape in the child.
+                    // The reference count added here will be decremented when the compound shape
+                    //     is destroyed in BSShapeCollection (the child shapes are looped over and dereferenced).
                     if (PhysicsScene.Shapes.ReferenceShape(cPrim.PhysShape))
                     {
                         PhysicsScene.Logger.ErrorFormat("{0} Rebuilt sharable shape when building linkset! Region={1}, primID={2}, shape={3}",
                                             LogHeader, PhysicsScene.RegionName, cPrim.LocalID, cPrim.PhysShape);
                     }
-                    BulletSimAPI.AddChildShapeToCompoundShape2(LinksetRoot.PhysShape.ptr, cPrim.PhysShape.ptr, displacementPos, displacementRot);
+                    BulletSimAPI.AddChildShapeToCompoundShape2(LinksetRoot.PhysShape.ptr, cPrim.PhysShape.ptr, lci.OffsetPos , lci.OffsetRot);
                 }
             }
 
-            // TODO: need to phantomize the child prims left behind.
-            //     Maybe just destroy the children bodies and shapes and have them rebuild on unlink.
-            //     Selection/deselection might cause way too many build/destructions esp. for LARGE linksets.
-
             return false;   // 'false' says to move onto the next child in the list
         });
 
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSPhysObject.cs b/OpenSim/Region/Physics/BulletSPlugin/BSPhysObject.cs
index b05d4ee..d2fc15c 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSPhysObject.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSPhysObject.cs
@@ -75,6 +75,7 @@ public abstract class BSPhysObject : PhysicsActor
     public string TypeName { get; protected set; }
 
     public BSLinkset Linkset { get; set; }
+    public BSLinksetInfo LinksetInfo { get; set; }
 
     // Return the object mass without calculating it or having side effects
     public abstract float RawMass { get; }
@@ -253,7 +254,9 @@ public abstract class BSPhysObject : PhysicsActor
         SubscribedEventsMs = 0;
         PhysicsScene.TaintedObject(TypeName+".UnSubscribeEvents", delegate()
         {
-            CurrentCollisionFlags = BulletSimAPI.RemoveFromCollisionFlags2(PhysBody.ptr, CollisionFlags.BS_SUBSCRIBE_COLLISION_EVENTS);
+            // Make sure there is a body there because sometimes destruction happens in an un-ideal order.
+            if (PhysBody.HasPhysicalBody)
+                CurrentCollisionFlags = BulletSimAPI.RemoveFromCollisionFlags2(PhysBody.ptr, CollisionFlags.BS_SUBSCRIBE_COLLISION_EVENTS);
         });
     }
     // Return 'true' if the simulator wants collision events
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSPrim.cs b/OpenSim/Region/Physics/BulletSPlugin/BSPrim.cs
index 627393a..d1d100d 100644
--- a/OpenSim/Region/Physics/BulletSPlugin/BSPrim.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSPrim.cs
@@ -108,8 +108,8 @@ public sealed class BSPrim : BSPhysObject
         _mass = CalculateMass();
 
         // No body or shape yet
-        PhysBody = new BulletBody(LocalID, IntPtr.Zero);
-        PhysShape = new BulletShape(IntPtr.Zero);
+        PhysBody = new BulletBody(LocalID);
+        PhysShape = new BulletShape();
 
         DetailLog("{0},BSPrim.constructor,call", LocalID);
         // do the actual object creation at taint time
@@ -143,7 +143,9 @@ public sealed class BSPrim : BSPhysObject
             DetailLog("{0},BSPrim.Destroy,taint,", LocalID);
             // If there are physical body and shape, release my use of same.
             PhysicsScene.Shapes.DereferenceBody(PhysBody, true, null);
+            PhysBody.Clear();
             PhysicsScene.Shapes.DereferenceShape(PhysShape, true, null);
+            PhysShape.Clear();
         });
     }
 
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSShapeCollection.cs b/OpenSim/Region/Physics/BulletSPlugin/BSShapeCollection.cs
index 933f573..74b4371 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSShapeCollection.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSShapeCollection.cs
@@ -149,7 +149,7 @@ public sealed class BSShapeCollection : IDisposable
     // Called when releasing use of a BSBody. BSShape is handled separately.
     public void DereferenceBody(BulletBody body, bool inTaintTime, BodyDestructionCallback bodyCallback )
     {
-        if (body.ptr == IntPtr.Zero)
+        if (!body.HasPhysicalBody)
             return;
 
         lock (m_collectionActivityLock)
@@ -243,12 +243,12 @@ public sealed class BSShapeCollection : IDisposable
     // Release the usage of a shape.
     public void DereferenceShape(BulletShape shape, bool inTaintTime, ShapeDestructionCallback shapeCallback)
     {
-        if (shape.ptr == IntPtr.Zero)
+        if (!shape.HasPhysicalShape)
             return;
 
         PhysicsScene.TaintedObject(inTaintTime, "BSShapeCollection.DereferenceShape", delegate()
         {
-            if (shape.ptr != IntPtr.Zero)
+            if (shape.HasPhysicalShape)
             {
                 if (shape.isNativeShape)
                 {
@@ -440,7 +440,7 @@ public sealed class BSShapeCollection : IDisposable
     }
 
     // Create a mesh/hull shape or a native shape if 'nativeShapePossible' is 'true'.
-    private bool CreateGeomNonSpecial(bool forceRebuild, BSPhysObject prim, ShapeDestructionCallback shapeCallback)
+    public bool CreateGeomNonSpecial(bool forceRebuild, BSPhysObject prim, ShapeDestructionCallback shapeCallback)
     {
         bool ret = false;
         bool haveShape = false;
@@ -573,7 +573,7 @@ public sealed class BSShapeCollection : IDisposable
             // Native shapes are scaled in Bullet so set the scaling to the size
             newShape = new BulletShape(BulletSimAPI.BuildNativeShape2(PhysicsScene.World.ptr, nativeShapeData), shapeType);
         }
-        if (newShape.ptr == IntPtr.Zero)
+        if (!newShape.HasPhysicalShape)
         {
             PhysicsScene.Logger.ErrorFormat("{0} BuildPhysicalNativeShape failed. ID={1}, shape={2}",
                                     LogHeader, prim.LocalID, shapeType);
@@ -590,7 +590,7 @@ public sealed class BSShapeCollection : IDisposable
     // Called at taint-time!
     private bool GetReferenceToMesh(BSPhysObject prim, ShapeDestructionCallback shapeCallback)
     {
-        BulletShape newShape = new BulletShape(IntPtr.Zero);
+        BulletShape newShape = new BulletShape();
 
         float lod;
         System.UInt64 newMeshKey = ComputeShapeKey(prim.Size, prim.BaseShape, out lod);
@@ -860,7 +860,7 @@ public sealed class BSShapeCollection : IDisposable
     private BulletShape VerifyMeshCreated(BulletShape newShape, BSPhysObject prim)
     {
         // If the shape was successfully created, nothing more to do
-        if (newShape.ptr != IntPtr.Zero)
+        if (newShape.HasPhysicalShape)
             return newShape;
 
         // If this mesh has an underlying asset and we have not failed getting it before, fetch the asset
@@ -919,7 +919,7 @@ public sealed class BSShapeCollection : IDisposable
         bool ret = false;
 
         // the mesh, hull or native shape must have already been created in Bullet
-        bool mustRebuild = (prim.PhysBody.ptr == IntPtr.Zero);
+        bool mustRebuild = !prim.PhysBody.HasPhysicalBody;
 
         // If there is an existing body, verify it's of an acceptable type.
         // If not a solid object, body is a GhostObject. Otherwise a RigidBody.
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainHeightmap.cs b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainHeightmap.cs
index 83b9c37..2d379bb 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainHeightmap.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainHeightmap.cs
@@ -136,7 +136,7 @@ public sealed class BSTerrainHeightmap : BSTerrainPhys
     {
         if (m_mapInfo != null)
         {
-            if (m_mapInfo.terrainBody.ptr != IntPtr.Zero)
+            if (m_mapInfo.terrainBody.HasPhysicalBody)
             {
                 BulletSimAPI.RemoveObjectFromWorld2(PhysicsScene.World.ptr, m_mapInfo.terrainBody.ptr);
                 // Frees both the body and the shape.
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs
index 83df360..c28d69d 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs
@@ -151,13 +151,13 @@ public sealed class BSTerrainManager
     // Release all the terrain structures we might have allocated
     public void ReleaseGroundPlaneAndTerrain()
     {
-        if (m_groundPlane.ptr != IntPtr.Zero)
+        if (m_groundPlane.HasPhysicalBody)
         {
             if (BulletSimAPI.RemoveObjectFromWorld2(PhysicsScene.World.ptr, m_groundPlane.ptr))
             {
                 BulletSimAPI.DestroyObject2(PhysicsScene.World.ptr, m_groundPlane.ptr);
             }
-            m_groundPlane.ptr = IntPtr.Zero;
+            m_groundPlane.Clear();
         }
 
         ReleaseTerrain();
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainMesh.cs b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainMesh.cs
index 6ce767d..3473006 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainMesh.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainMesh.cs
@@ -94,7 +94,7 @@ public sealed class BSTerrainMesh : BSTerrainPhys
         m_terrainShape = new BulletShape(BulletSimAPI.CreateMeshShape2(PhysicsScene.World.ptr,
                                                     indicesCount, indices, verticesCount, vertices),
                                         BSPhysicsShapeType.SHAPE_MESH);
-        if (m_terrainShape.ptr == IntPtr.Zero)
+        if (!m_terrainShape.HasPhysicalShape)
         {
             // DISASTER!!
             PhysicsScene.DetailLog("{0},BSTerrainMesh.create,failedCreationOfShape", ID);
@@ -107,7 +107,7 @@ public sealed class BSTerrainMesh : BSTerrainPhys
         Quaternion rot = Quaternion.Identity;
 
         m_terrainBody = new BulletBody(id, BulletSimAPI.CreateBodyWithDefaultMotionState2( m_terrainShape.ptr, ID, pos, rot));
-        if (m_terrainBody.ptr == IntPtr.Zero)
+        if (!m_terrainBody.HasPhysicalBody)
         {
             // DISASTER!!
             physicsScene.Logger.ErrorFormat("{0} Failed creation of terrain body! base={1}", LogHeader, TerrainBase);
@@ -140,7 +140,7 @@ public sealed class BSTerrainMesh : BSTerrainPhys
 
     public override void Dispose()
     {
-        if (m_terrainBody.ptr != IntPtr.Zero)
+        if (m_terrainBody.HasPhysicalBody)
         {
             BulletSimAPI.RemoveObjectFromWorld2(PhysicsScene.World.ptr, m_terrainBody.ptr);
             // Frees both the body and the shape.
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BulletSimAPI.cs b/OpenSim/Region/Physics/BulletSPlugin/BulletSimAPI.cs
index 2671995..1559025 100644
--- a/OpenSim/Region/Physics/BulletSPlugin/BulletSimAPI.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BulletSimAPI.cs
@@ -53,6 +53,9 @@ public struct BulletSim
 // An allocated Bullet btRigidBody
 public struct BulletBody
 {
+    public BulletBody(uint id) : this(id, IntPtr.Zero)
+    {
+    }
     public BulletBody(uint id, IntPtr xx)
     {
         ID = id;
@@ -64,6 +67,13 @@ public struct BulletBody
     public uint ID;
     public CollisionFilterGroups collisionGroup;
     public CollisionFilterGroups collisionMask;
+
+    public void Clear()
+    {
+        ptr = IntPtr.Zero;
+    }
+    public bool HasPhysicalBody { get { return ptr != IntPtr.Zero; } }
+
     public override string ToString()
     {
         StringBuilder buff = new StringBuilder();
@@ -103,6 +113,13 @@ public struct BulletShape
     public BSPhysicsShapeType type;
     public System.UInt64 shapeKey;
     public bool isNativeShape;
+
+    public void Clear()
+    {
+        ptr = IntPtr.Zero;
+    }
+    public bool HasPhysicalShape { get { return ptr != IntPtr.Zero; } }
+
     public override string ToString()
     {
         StringBuilder buff = new StringBuilder();
@@ -140,6 +157,12 @@ public struct BulletConstraint
         ptr = xx;
     }
     public IntPtr ptr;
+
+    public void Clear()
+    {
+        ptr = IntPtr.Zero;
+    }
+    public bool HasPhysicalConstraint { get { return ptr != IntPtr.Zero; } }
 }
 
 // An allocated HeightMapThing which holds various heightmap info.