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diff --git a/OpenSim/Region/Physics/BulletSNPlugin/BSLinksetConstraints.cs b/OpenSim/Region/Physics/BulletSNPlugin/BSLinksetConstraints.cs
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+++ b/OpenSim/Region/Physics/BulletSNPlugin/BSLinksetConstraints.cs
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+/*
+ * Copyright (c) Contributors, http://opensimulator.org/
+ * See CONTRIBUTORS.TXT for a full list of copyright holders.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyrightD
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of the OpenSimulator Project nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+using OMV = OpenMetaverse;
+
+namespace OpenSim.Region.Physics.BulletSNPlugin
+{
+public sealed class BSLinksetConstraints : BSLinkset
+{
+    // private static string LogHeader = "[BULLETSIM LINKSET CONSTRAINTS]";
+
+    public BSLinksetConstraints(BSScene scene, BSPhysObject parent) : base(scene, parent)
+    {
+    }
+
+    // When physical properties are changed the linkset needs to recalculate
+    //   its internal properties.
+    // This is queued in the 'post taint' queue so the
+    //   refresh will happen once after all the other taints are applied.
+    public override void Refresh(BSPhysObject requestor)
+    {
+        // Queue to happen after all the other taint processing
+        PhysicsScene.PostTaintObject("BSLinksetContraints.Refresh", requestor.LocalID, delegate()
+            {
+                if (HasAnyChildren && IsRoot(requestor))
+                    RecomputeLinksetConstraints();
+            });
+    }
+
+    // The object is going dynamic (physical). Do any setup necessary
+    //     for a dynamic linkset.
+    // Only the state of the passed object can be modified. The rest of the linkset
+    //     has not yet been fully constructed.
+    // Return 'true' if any properties updated on the passed object.
+    // Called at taint-time!
+    public override bool MakeDynamic(BSPhysObject child)
+    {
+        // What is done for each object in BSPrim is what we want.
+        return false;
+    }
+
+    // The object is going static (non-physical). Do any setup necessary for a static linkset.
+    // Return 'true' if any properties updated on the passed object.
+    // This doesn't normally happen -- OpenSim removes the objects from the physical
+    //     world if it is a static linkset.
+    // Called at taint-time!
+    public override bool MakeStatic(BSPhysObject child)
+    {
+        // What is done for each object in BSPrim is what we want.
+        return false;
+    }
+
+    // Called at taint-time!!
+    public override void UpdateProperties(BSPhysObject updated, bool inTaintTime)
+    {
+        // Nothing to do for constraints on property updates
+    }
+
+    // Routine called when rebuilding the body of some member of the linkset.
+    // Destroy all the constraints have have been made to root and set
+    //     up to rebuild the constraints before the next simulation step.
+    // Returns 'true' of something was actually removed and would need restoring
+    // Called at taint-time!!
+    public override bool RemoveBodyDependencies(BSPrim child)
+    {
+        bool ret = false;
+
+        DetailLog("{0},BSLinksetConstraint.RemoveBodyDependencies,removeChildrenForRoot,rID={1},rBody={2}",
+                                    child.LocalID, LinksetRoot.LocalID, LinksetRoot.PhysBody.ptr.ToString());
+
+        lock (m_linksetActivityLock)
+        {
+            // Just undo all the constraints for this linkset. Rebuild at the end of the step.
+            ret = PhysicallyUnlinkAllChildrenFromRoot(LinksetRoot);
+            // Cause the constraints, et al to be rebuilt before the next simulation step.
+            Refresh(LinksetRoot);
+        }
+        return ret;
+    }
+
+    // Companion to RemoveBodyDependencies(). If RemoveBodyDependencies() returns 'true',
+    // this routine will restore the removed constraints.
+    // Called at taint-time!!
+    public override void RestoreBodyDependencies(BSPrim child)
+    {
+        // The Refresh operation queued by RemoveBodyDependencies() will build any missing constraints.
+    }
+
+    // ================================================================
+
+    // Add a new child to the linkset.
+    // Called while LinkActivity is locked.
+    protected override void AddChildToLinkset(BSPhysObject child)
+    {
+        if (!HasChild(child))
+        {
+            m_children.Add(child);
+
+            DetailLog("{0},BSLinksetConstraints.AddChildToLinkset,call,child={1}", LinksetRoot.LocalID, child.LocalID);
+
+            // Cause constraints and assorted properties to be recomputed before the next simulation step.
+            Refresh(LinksetRoot);
+        }
+        return;
+    }
+
+    // Remove the specified child from the linkset.
+    // Safe to call even if the child is not really in my linkset.
+    protected override void RemoveChildFromLinkset(BSPhysObject child)
+    {
+        if (m_children.Remove(child))
+        {
+            BSPhysObject rootx = LinksetRoot; // capture the root and body as of now
+            BSPhysObject childx = child;
+
+            DetailLog("{0},BSLinksetConstraints.RemoveChildFromLinkset,call,rID={1},rBody={2},cID={3},cBody={4}",
+                            childx.LocalID,
+                            rootx.LocalID, rootx.PhysBody.ptr.ToString(),
+                            childx.LocalID, childx.PhysBody.ptr.ToString());
+
+            PhysicsScene.TaintedObject("BSLinksetConstraints.RemoveChildFromLinkset", delegate()
+            {
+                PhysicallyUnlinkAChildFromRoot(rootx, childx);
+            });
+            // See that the linkset parameters are recomputed at the end of the taint time.
+            Refresh(LinksetRoot);
+        }
+        else
+        {
+            // Non-fatal occurance.
+            // PhysicsScene.Logger.ErrorFormat("{0}: Asked to remove child from linkset that was not in linkset", LogHeader);
+        }
+        return;
+    }
+
+    // Create a constraint between me (root of linkset) and the passed prim (the child).
+    // Called at taint time!
+    private void PhysicallyLinkAChildToRoot(BSPhysObject rootPrim, BSPhysObject childPrim)
+    {
+        // Don't build the constraint when asked. Put it off until just before the simulation step.
+        Refresh(rootPrim);
+    }
+
+    private BSConstraint BuildConstraint(BSPhysObject rootPrim, BSPhysObject childPrim)
+    {
+        // Zero motion for children so they don't interpolate
+        childPrim.ZeroMotion(true);
+
+        // Relative position normalized to the root prim
+        // Essentually a vector pointing from center of rootPrim to center of childPrim
+        OMV.Vector3 childRelativePosition = childPrim.Position - rootPrim.Position;
+
+        // real world coordinate of midpoint between the two objects
+        OMV.Vector3 midPoint = rootPrim.Position + (childRelativePosition / 2);
+
+        DetailLog("{0},BSLinksetConstraint.BuildConstraint,taint,root={1},rBody={2},child={3},cBody={4},rLoc={5},cLoc={6},midLoc={7}",
+                                        rootPrim.LocalID,
+                                        rootPrim.LocalID, rootPrim.PhysBody.ptr.ToString(),
+                                        childPrim.LocalID, childPrim.PhysBody.ptr.ToString(),
+                                        rootPrim.Position, childPrim.Position, midPoint);
+
+        // create a constraint that allows no freedom of movement between the two objects
+        // http://bulletphysics.org/Bullet/phpBB3/viewtopic.php?t=4818
+
+        BSConstraint6Dof constrain = new BSConstraint6Dof(
+                            PhysicsScene.World, rootPrim.PhysBody, childPrim.PhysBody, midPoint, true, true );
+                            // PhysicsScene.World, childPrim.BSBody, rootPrim.BSBody, midPoint, true, true );
+
+        /* NOTE: below is an attempt to build constraint with full frame computation, etc.
+         *     Using the midpoint is easier since it lets the Bullet code manipulate the transforms
+         *     of the objects.
+         * Code left for future programmers.
+        // ==================================================================================
+        // relative position normalized to the root prim
+        OMV.Quaternion invThisOrientation = OMV.Quaternion.Inverse(rootPrim.Orientation);
+        OMV.Vector3 childRelativePosition = (childPrim.Position - rootPrim.Position) * invThisOrientation;
+
+        // relative rotation of the child to the parent
+        OMV.Quaternion childRelativeRotation = invThisOrientation * childPrim.Orientation;
+        OMV.Quaternion inverseChildRelativeRotation = OMV.Quaternion.Inverse(childRelativeRotation);
+
+        DetailLog("{0},BSLinksetConstraint.PhysicallyLinkAChildToRoot,taint,root={1},child={2}", rootPrim.LocalID, rootPrim.LocalID, childPrim.LocalID);
+        BS6DofConstraint constrain = new BS6DofConstraint(
+                        PhysicsScene.World, rootPrim.Body, childPrim.Body,
+                        OMV.Vector3.Zero,
+                        OMV.Quaternion.Inverse(rootPrim.Orientation),
+                        OMV.Vector3.Zero,
+                        OMV.Quaternion.Inverse(childPrim.Orientation),
+                        true,
+                        true
+                        );
+        // ==================================================================================
+        */
+
+        PhysicsScene.Constraints.AddConstraint(constrain);
+
+        // zero linear and angular limits makes the objects unable to move in relation to each other
+        constrain.SetLinearLimits(OMV.Vector3.Zero, OMV.Vector3.Zero);
+        constrain.SetAngularLimits(OMV.Vector3.Zero, OMV.Vector3.Zero);
+
+        // tweek the constraint to increase stability
+        constrain.UseFrameOffset(BSParam.BoolNumeric(BSParam.LinkConstraintUseFrameOffset));
+        constrain.TranslationalLimitMotor(BSParam.BoolNumeric(BSParam.LinkConstraintEnableTransMotor),
+                        BSParam.LinkConstraintTransMotorMaxVel,
+                        BSParam.LinkConstraintTransMotorMaxForce);
+        constrain.SetCFMAndERP(BSParam.LinkConstraintCFM, BSParam.LinkConstraintERP);
+        if (BSParam.LinkConstraintSolverIterations != 0f)
+        {
+            constrain.SetSolverIterations(BSParam.LinkConstraintSolverIterations);
+        }
+        return constrain;
+    }
+
+    // Remove linkage between the linkset root and a particular child
+    // The root and child bodies are passed in because we need to remove the constraint between
+    //      the bodies that were present at unlink time.
+    // Called at taint time!
+    private bool PhysicallyUnlinkAChildFromRoot(BSPhysObject rootPrim, BSPhysObject childPrim)
+    {
+        bool ret = false;
+        DetailLog("{0},BSLinksetConstraint.PhysicallyUnlinkAChildFromRoot,taint,root={1},rBody={2},child={3},cBody={4}",
+                            rootPrim.LocalID,
+                            rootPrim.LocalID, rootPrim.PhysBody.ptr.ToString(),
+                            childPrim.LocalID, childPrim.PhysBody.ptr.ToString());
+
+        // Find the constraint for this link and get rid of it from the overall collection and from my list
+        if (PhysicsScene.Constraints.RemoveAndDestroyConstraint(rootPrim.PhysBody, childPrim.PhysBody))
+        {
+            // Make the child refresh its location
+            BulletSimAPI.PushUpdate2(childPrim.PhysBody.ptr);
+            ret = true;
+        }
+
+        return ret;
+    }
+
+    // Remove linkage between myself and any possible children I might have.
+    // Returns 'true' of any constraints were destroyed.
+    // Called at taint time!
+    private bool PhysicallyUnlinkAllChildrenFromRoot(BSPhysObject rootPrim)
+    {
+        DetailLog("{0},BSLinksetConstraint.PhysicallyUnlinkAllChildren,taint", rootPrim.LocalID);
+
+        return PhysicsScene.Constraints.RemoveAndDestroyConstraint(rootPrim.PhysBody);
+    }
+
+    // Call each of the constraints that make up this linkset and recompute the
+    //    various transforms and variables. Create constraints of not created yet.
+    // Called before the simulation step to make sure the constraint based linkset
+    //    is all initialized.
+    // Called at taint time!!
+    private void RecomputeLinksetConstraints()
+    {
+        float linksetMass = LinksetMass;
+        LinksetRoot.UpdatePhysicalMassProperties(linksetMass);
+
+        // DEBUG: see of inter-linkset collisions are causing problems
+        // BulletSimAPI.SetCollisionFilterMask2(LinksetRoot.BSBody.ptr, 
+        //                     (uint)CollisionFilterGroups.LinksetFilter, (uint)CollisionFilterGroups.LinksetMask);
+        DetailLog("{0},BSLinksetConstraint.RecomputeLinksetConstraints,set,rBody={1},linksetMass={2}",
+                            LinksetRoot.LocalID, LinksetRoot.PhysBody.ptr.ToString(), linksetMass);
+
+        foreach (BSPhysObject child in m_children)
+        {
+            // A child in the linkset physically shows the mass of the whole linkset.
+            // This allows Bullet to apply enough force on the child to move the whole linkset.
+            // (Also do the mass stuff before recomputing the constraint so mass is not zero.)
+            child.UpdatePhysicalMassProperties(linksetMass);
+
+            BSConstraint constrain;
+            if (!PhysicsScene.Constraints.TryGetConstraint(LinksetRoot.PhysBody, child.PhysBody, out constrain))
+            {
+                // If constraint doesn't exist yet, create it.
+                constrain = BuildConstraint(LinksetRoot, child);
+            }
+            constrain.RecomputeConstraintVariables(linksetMass);
+
+            // DEBUG: see of inter-linkset collisions are causing problems
+            // BulletSimAPI.SetCollisionFilterMask2(child.BSBody.ptr, 
+            //                 (uint)CollisionFilterGroups.LinksetFilter, (uint)CollisionFilterGroups.LinksetMask);
+
+            // BulletSimAPI.DumpConstraint2(PhysicsScene.World.ptr, constrain.Constraint.ptr);    // DEBUG DEBUG
+        }
+
+    }
+}
+}