public override void CollDetect(CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor)
        {
            Vector3 body0Pos = (info.Skin0.Owner != null) ? info.Skin0.Owner.OldPosition : Vector3.Zero;
            Vector3 body1Pos = (info.Skin1.Owner != null) ? info.Skin1.Owner.OldPosition : Vector3.Zero;

            // todo - proper swept test
            Capsule oldCapsule0 = (Capsule)info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0);
            Capsule newCapsule0 = (Capsule)info.Skin0.GetPrimitiveNewWorld(info.IndexPrim0);
            Segment oldSeg0 = new Segment(oldCapsule0.Position, oldCapsule0.Length * oldCapsule0.Orientation.Backward);
            Segment newSeg0 = new Segment(newCapsule0.Position, newCapsule0.Length * newCapsule0.Orientation.Backward);

            Capsule oldCapsule1 = (Capsule)info.Skin1.GetPrimitiveOldWorld(info.IndexPrim1);
            Capsule newCapsule1 = (Capsule)info.Skin1.GetPrimitiveNewWorld(info.IndexPrim1);
            Segment oldSeg1 = new Segment(oldCapsule1.Position, oldCapsule1.Length * oldCapsule1.Orientation.Backward);
            Segment newSeg1 = new Segment(newCapsule1.Position, newCapsule1.Length * newCapsule1.Orientation.Backward);

            float radSum = newCapsule0.Radius + newCapsule1.Radius;

            float oldt0, oldt1;
            float newt0, newt1;
            float oldDistSq = Distance.SegmentSegmentDistanceSq(out oldt0, out oldt1, oldSeg0, oldSeg1);
            float newDistSq = Distance.SegmentSegmentDistanceSq(out newt0, out newt1, newSeg0, newSeg1);

            if (System.Math.Min(oldDistSq, newDistSq) < ((radSum + collTolerance) * (radSum + collTolerance)))
            {
                Vector3 pos0 = oldSeg0.GetPoint(oldt0);
                Vector3 pos1 = oldSeg1.GetPoint(oldt1);

                Vector3 delta = pos0 - pos1;

                float dist = (float)System.Math.Sqrt((float)oldDistSq);
                float depth = radSum - dist;

                if (dist > JiggleMath.Epsilon)
                {
                    delta /= dist;
                }
                else
                {
                    // todo - make this not random
                    delta = Vector3.Transform(Vector3.Backward, Matrix.CreateFromAxisAngle(Vector3.Up, MathHelper.ToRadians(random.Next(360))));
                }

                Vector3 worldPos = pos1 +
                    (oldCapsule1.Radius - 0.5f * depth) * delta;

                unsafe
                {
                    SmallCollPointInfo collInfo = new SmallCollPointInfo(worldPos - body0Pos, worldPos - body1Pos, depth);
                    collisionFunctor.CollisionNotify(ref info, ref delta, &collInfo, 1);
                }

            }
        }

        /// <summary>
        /// 
        /// </summary>
        /// <param name="info"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        public override void CollDetect(CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor)
        {
            if (info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0).Type == this.Type1)
            {
                CollisionSkin skinSwap = info.Skin0;
                info.Skin0 = info.Skin1;
                info.Skin1 = skinSwap;
                int primSwap = info.IndexPrim0;
                info.IndexPrim0 = info.IndexPrim1;
                info.IndexPrim1 = primSwap;
            }

            Vector3 body0Pos = (info.Skin0.Owner != null) ? info.Skin0.Owner.OldPosition : Vector3.Zero;
            Vector3 body1Pos = (info.Skin1.Owner != null) ? info.Skin1.Owner.OldPosition : Vector3.Zero;

            // todo - proper swept test
            Sphere oldSphere = (Sphere)info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0);
            Sphere newSphere = (Sphere)info.Skin0.GetPrimitiveNewWorld(info.IndexPrim0);

            JigLibX.Geometry.Plane oldPlane = (JigLibX.Geometry.Plane)info.Skin1.GetPrimitiveOldWorld(info.IndexPrim1);
            JigLibX.Geometry.Plane newPlane = (JigLibX.Geometry.Plane)info.Skin1.GetPrimitiveNewWorld(info.IndexPrim1);

            Matrix newPlaneInvTransform = newPlane.InverseTransformMatrix;
            Matrix oldPlaneInvTransform = oldPlane.InverseTransformMatrix;

            Vector3 oldSpherePos = Vector3.Transform(oldSphere.Position, oldPlaneInvTransform);
            Vector3 newSpherePos = Vector3.Transform(newSphere.Position, newPlaneInvTransform);

            // consider it a contact if either old or new are touching
            float oldDist = Distance.PointPlaneDistance(oldSpherePos, oldPlane);
            float newDist = Distance.PointPlaneDistance(newSpherePos, newPlane);

            if (System.Math.Min(newDist, oldDist) > collTolerance + newSphere.Radius)
                return;

            // collision - record depth using the old values
            float oldDepth = oldSphere.Radius - oldDist;

            // calc the world position based on the old position(s)
            Vector3 worldPos = oldSphere.Position - oldSphere.Radius * oldPlane.Normal;

            unsafe
            {
                SmallCollPointInfo collInfo = new SmallCollPointInfo(worldPos - body0Pos, worldPos - body1Pos, oldDepth);
                collisionFunctor.CollisionNotify(ref info, ref oldPlane.normal, &collInfo, 1);
            }
        }

        /// <summary>
        /// Detect BoxStaticMesh Collisions.
        /// </summary>
        /// <param name="info"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        public override void CollDetect(CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor)
        {
            if (info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0).Type == Type1)
            {
                CollisionSkin skinSwap = info.Skin0;
                info.Skin0 = info.Skin1;
                info.Skin1 = skinSwap;
                int primSwap = info.IndexPrim0;
                info.IndexPrim0 = info.IndexPrim1;
                info.IndexPrim1 = primSwap;
            }

            if (info.Skin0.CollisionSystem != null && info.Skin0.CollisionSystem.UseSweepTests)
                CollDetectSweep(ref info, collTolerance, collisionFunctor);
            else
                CollDetectOverlap(ref info, collTolerance, collisionFunctor);
        }

        /// <summary>
        /// CollDetect
        /// </summary>
        /// <param name="info"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        public override void CollDetect(CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor)
        {
            Vector3 body0Pos = (info.Skin0.Owner != null) ? info.Skin0.Owner.OldPosition : Vector3.Zero;
            Vector3 body1Pos = (info.Skin1.Owner != null) ? info.Skin1.Owner.OldPosition : Vector3.Zero;

            // todo - proper swept test
            Sphere oldSphere0 = (Sphere) info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0);
            Sphere newSphere0 = (Sphere)info.Skin0.GetPrimitiveNewWorld(info.IndexPrim0);
            Sphere oldSphere1 = (Sphere)info.Skin1.GetPrimitiveOldWorld(info.IndexPrim1);
            Sphere newSphere1 = (Sphere)info.Skin1.GetPrimitiveNewWorld(info.IndexPrim1);

            Vector3 oldDelta = oldSphere0.Position - oldSphere1.Position;
            Vector3 newDelta = newSphere0.Position - oldSphere1.Position;

            float oldDistSq = oldDelta.LengthSquared;
            float newDistSq = newDelta.LengthSquared;

            float radSum = newSphere0.Radius + newSphere1.Radius;

            if (System.Math.Min(oldDistSq, newDistSq) < ((radSum + collTolerance) * (radSum + collTolerance)))
            {
                float oldDist = (float)System.Math.Sqrt((float)oldDistSq);
                float depth = radSum - oldDist;

                if (oldDist > JiggleMath.Epsilon)
                {
                    oldDelta /= oldDist;
                }
                else
                {
                    // TODO - make this not random...!
                    oldDelta = Vector3Extensions.TransformNormal(Vector3Extensions.Backward, Matrix4.CreateFromAxisAngle(Vector3Extensions.Up, OpenTKHelper.ToRadians(random.Next(360))));
                }

                Vector3 worldPos = oldSphere1.Position +
                    (oldSphere1.Radius - 0.5f * depth) * oldDelta;

                unsafe
                {
                    SmallCollPointInfo collInfo = new SmallCollPointInfo(worldPos - body0Pos, worldPos - body1Pos, depth);

                    collisionFunctor.CollisionNotify(ref info, ref oldDelta, &collInfo, 1);
                }
            }
        }

        /// <summary>
        /// CollDetect
        /// </summary>
        /// <param name="info"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        public override void CollDetect(CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor)
        {
            // get the skins in the order that we're expecting
            if (info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0).Type == this.Type1)
            {
                CollisionSkin skinSwap = info.Skin0;
                info.Skin0 = info.Skin1;
                info.Skin1 = skinSwap;
                int primSwap = info.IndexPrim0;
                info.IndexPrim0 = info.IndexPrim1;
                info.IndexPrim1 = primSwap;
            }

            if((info.Skin0.CollisionSystem != null) && info.Skin0.CollisionSystem.UseSweepTests)
                CollDetectSweep(info, collTolerance, collisionFunctor);
            else
                CollDetectOverlap(info, collTolerance, collisionFunctor);
        }

        /// <summary>
        /// 
        /// </summary>
        /// <param name="infoOrig"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        public override void CollDetect(CollDetectInfo infoOrig, float collTolerance, CollisionFunctor collisionFunctor)
        {
            CollDetectInfo info = infoOrig;
            if (info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0).Type == this.Type1)
            {
                CollisionSkin skinSwap = info.Skin0;
                info.Skin0 = info.Skin1;
                info.Skin1 = skinSwap;
                int primSwap = info.IndexPrim0;
                info.IndexPrim0 = info.IndexPrim1;
                info.IndexPrim1 = primSwap;
            }

            Vector3 body0Pos = (info.Skin0.Owner != null) ? info.Skin0.Owner.OldPosition : Vector3.Zero;
            Vector3 body1Pos = (info.Skin1.Owner != null) ? info.Skin1.Owner.OldPosition : Vector3.Zero;

            // todo - proper swept test
            Sphere oldSphere = (Sphere)info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0);
            Sphere newSphere = (Sphere)info.Skin0.GetPrimitiveNewWorld(info.IndexPrim0);

            Heightmap oldHeightmap = (Heightmap)info.Skin1.GetPrimitiveOldWorld(info.IndexPrim1);
            Heightmap newHeightmap = (Heightmap)info.Skin1.GetPrimitiveNewWorld(info.IndexPrim1);

            float newDist;
            Vector3 normal;
            newHeightmap.GetHeightAndNormal(out newDist, out normal,newSphere.Position);
            if (newDist < collTolerance + newSphere.Radius)
            {
                float oldDist = oldHeightmap.GetHeight(oldSphere.Position);
                float depth = oldSphere.Radius - oldDist;

                // calc the world position when it just hit
                Vector3 oldPt = oldSphere.Position - oldSphere.Radius * normal;
                unsafe
                {
                    SmallCollPointInfo ptInfo = new SmallCollPointInfo(oldPt - body0Pos, oldPt - body1Pos, depth);

                    collisionFunctor.CollisionNotify(ref info, ref normal, &ptInfo, 1);
                }
            }
        }

        /// <summary>
        /// CollDetect
        /// </summary>
        /// <param name="infoOrig"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        public override void CollDetect(CollDetectInfo infoOrig, float collTolerance, CollisionFunctor collisionFunctor)
        {
           // get the skins in the order that we're expecting
            CollDetectInfo info = infoOrig;

            if (info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0).Type == this.Type1)
            {
                CollisionSkin skinSwap = info.Skin0;
                info.Skin0 = info.Skin1;
                info.Skin1 = skinSwap;
                int primSwap = info.IndexPrim0;
                info.IndexPrim0 = info.IndexPrim1;
                info.IndexPrim1 = primSwap;
            }

            Vector3 body0Pos = (info.Skin0.Owner != null) ? info.Skin0.Owner.OldPosition : Vector3.Zero;
            Vector3 body1Pos = (info.Skin1.Owner != null) ? info.Skin1.Owner.OldPosition : Vector3.Zero;

            // todo - proper sweep test
            Sphere oldSphere = info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0) as Sphere;
            Sphere newSphere = info.Skin0.GetPrimitiveNewWorld(info.IndexPrim0) as Sphere;

            Box oldBox = info.Skin1.GetPrimitiveOldWorld(info.IndexPrim1) as Box;
            Box newBox = info.Skin1.GetPrimitiveNewWorld(info.IndexPrim1) as Box;

            Vector3 oldBoxPoint;
            Vector3 newBoxPoint;

            float oldDist = oldBox.GetDistanceToPoint(out oldBoxPoint, oldSphere.Position);
            float newDist = newBox.GetDistanceToPoint(out newBoxPoint, newSphere.Position);

            // normally point will be outside
            float oldDepth = oldSphere.Radius - oldDist;
            float newDepth = newSphere.Radius - newDist;

            if (System.Math.Max(oldDepth, newDepth) > -collTolerance)
            {
                Vector3 dir;
                if (oldDist < -JiggleMath.Epsilon)
                {
                    dir = oldBoxPoint - oldSphere.Position - oldBoxPoint;
                    JiggleMath.NormalizeSafe(ref dir);
                }
                else if (oldDist > JiggleMath.Epsilon)
                {
                    dir = oldSphere.Position - oldBoxPoint;
                    JiggleMath.NormalizeSafe(ref dir);
                }
                else
                {
                    dir = oldSphere.Position - oldBox.GetCentre();
                    JiggleMath.NormalizeSafe(ref dir);
                }

                unsafe
                {
                    SmallCollPointInfo collInfo = new SmallCollPointInfo(oldBoxPoint - body0Pos,
                        oldBoxPoint - body1Pos, oldDepth);

                    
                    collisionFunctor.CollisionNotify(ref info, ref dir, &collInfo, 1);
                }

            }
        #endregion

        }

 /// <summary>
 /// 
 /// </summary>
 /// <param name="info"></param>
 /// <param name="collTolerance"></param>
 /// <param name="collisionFunctor"></param>
 public abstract void CollDetect(CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor);

        /// <summary>
        /// CollDetectSweep
        /// </summary>
        /// <param name="info"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        private void CollDetectSweep(ref CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor)
        {
            // todo - proper swept test
            // note - mesh is static and its triangles are in world space
            TriangleMesh mesh = info.Skin1.GetPrimitiveNewWorld(info.IndexPrim1) as TriangleMesh;

            Box oldBox = info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0) as Box;
            Box newBox = info.Skin0.GetPrimitiveNewWorld(info.IndexPrim0) as Box;

            Vector3 oldCentre;
            oldBox.GetCentre(out oldCentre);
            Vector3 newCentre;
            newBox.GetCentre(out newCentre);

            Vector3 delta;
            Vector3.Subtract(ref newCentre, ref oldCentre, out delta);

            float boxMinLen = 0.5f * System.Math.Min(newBox.SideLengths.X, System.Math.Min(newBox.SideLengths.Y, newBox.SideLengths.Z));
            int nPositions = 1 + (int)(delta.Length / boxMinLen);
            // limit the max positions...
            if (nPositions > 50)
            {
                System.Diagnostics.Debug.WriteLine("Warning - clamping max positions in swept box test");
                nPositions = 50;
            }
            if (nPositions == 1)
            {
                CollDetectBoxStaticMeshOverlap(oldBox, newBox, mesh,ref info, collTolerance, collisionFunctor);
            }
            else
            {
                BoundingBox bb = BoundingBoxHelper.InitialBox;
                BoundingBoxHelper.AddBox(oldBox, ref bb);
                BoundingBoxHelper.AddBox(newBox, ref bb);
                unsafe
                {
            #if USE_STACKALLOC
                    int* potentialTriangles = stackalloc int[MaxLocalStackTris];
                    {
            #else
                    int[] potTriArray = IntStackAlloc();
                    fixed( int* potentialTriangles = potTriArray)
                    {
            #endif
                        int numTriangles = mesh.GetTrianglesIntersectingtAABox(potentialTriangles, MaxLocalStackTris, ref bb);
                        if (numTriangles > 0)
                        {
                            for (int i = 0; i <= nPositions; ++i)
                            {
                                float frac = ((float)i) / nPositions;
                                Vector3 centre;
                                Vector3.Multiply(ref delta, frac, out centre);
                                Vector3.Add(ref centre, ref oldCentre, out centre);

                                Matrix4 orient = Matrix4Extensions.Add(Matrix4Extensions.Multiply(oldBox.Orientation, 1.0f - frac), Matrix4Extensions.Multiply(newBox.Orientation, frac));

                                Box box = new Box(centre - 0.5f * Vector3Extensions.TransformNormal(newBox.SideLengths, orient), orient, newBox.SideLengths);
                                // ideally we'd break if we get one collision... but that stops us getting multiple collisions
                                // when we enter a corner (two walls meeting) - can let us pass through
                                CollDetectBoxStaticMeshOverlap(oldBox, box, mesh, ref info, collTolerance, collisionFunctor);
                            }
                        }
            #if USE_STACKALLOC
                    }
            #else
                    }
                    FreeStackAlloc(potTriArray);
            #endif
                }
            }
        }

        /// <summary>
        /// Detect BoxHeightmap Collisions.
        /// </summary>
        /// <param name="infoOrig"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        public override void CollDetect(CollDetectInfo infoOrig, float collTolerance, CollisionFunctor collisionFunctor)
        {
            CollDetectInfo info = infoOrig;
            if (info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0).Type == this.Type1)
            {
                CollisionSkin skinSwap = info.Skin0;
                info.Skin0 = info.Skin1;
                info.Skin1 = skinSwap;
                int primSwap = info.IndexPrim0;
                info.IndexPrim0 = info.IndexPrim1;
                info.IndexPrim1 = primSwap;
            }

            Vector3 body0Pos = (info.Skin0.Owner != null) ? info.Skin0.Owner.OldPosition : Vector3.Zero;
            Vector3 body1Pos = (info.Skin1.Owner != null) ? info.Skin1.Owner.OldPosition : Vector3.Zero;

            // todo - proper swept test
            Box oldBox = info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0) as Box;
            Box newBox = info.Skin0.GetPrimitiveNewWorld(info.IndexPrim0) as Box;

            Heightmap oldHeightmap = info.Skin1.GetPrimitiveOldWorld(info.IndexPrim1) as Heightmap;
            Heightmap newHeightmap = info.Skin1.GetPrimitiveNewWorld(info.IndexPrim1) as Heightmap;

            Vector3[] oldPts, newPts;
            oldBox.GetCornerPoints(out oldPts);
            newBox.GetCornerPoints(out newPts);

            unsafe
            {
            #if USE_STACKALLOC
                SmallCollPointInfo* collPts = stackalloc SmallCollPointInfo[MaxLocalStackSCPI];
            #else
                SmallCollPointInfo[] collPtArray = SCPIStackAlloc();
                fixed (SmallCollPointInfo* collPts = collPtArray)
            #endif
                {
                    int numCollPts = 0;

                    Vector3 collNormal = Vector3.Zero;

                    for (int i = 0; i < 8; ++i)
                    {
                        Vector3 newPt = newPts[i];
                        float newDist;
                        Vector3 normal;
                        newHeightmap.GetHeightAndNormal(out newDist, out normal, newPt);

                        if (newDist < collTolerance)
                        {
                            Vector3 oldPt = oldPts[i];
                            float oldDist = oldHeightmap.GetHeight(oldPt);

                            #region REFERENCE: collPts.Add(new CollPointInfo(oldPt - body0Pos, oldPt - body1Pos, -oldDist));
                            Vector3 pt0;
                            Vector3 pt1;
                            Vector3.Subtract(ref oldPt, ref body0Pos, out pt0);
                            Vector3.Subtract(ref oldPt, ref body1Pos, out pt1);
                            if (numCollPts < MaxLocalStackSCPI)
                            {
                                collPts[numCollPts++] = new SmallCollPointInfo(ref pt0, ref pt1, -oldDist);
                            }
                            #endregion

                            #region REFERENCE: collNormal += normal;
                            Vector3.Add(ref collNormal, ref normal, out collNormal);
                            #endregion
                        }
                    }

                    if (numCollPts > 0)
                    {
                        JiggleMath.NormalizeSafe(ref collNormal);
                        collisionFunctor.CollisionNotify(ref info, ref collNormal, collPts, numCollPts);
                    }
                }
            #if !USE_STACKALLOC
                FreeStackAlloc(collPtArray);
            #endif
            }
        }

 /// <summary>
 /// As DetectCollisions but detects for all bodies, testing each pair 
 /// only once
 /// </summary>
 /// <param name="bodies"></param>
 /// <param name="collisionFunctor"></param>
 /// <param name="collisionPredicate"></param>
 /// <param name="collTolerance"></param>
 public abstract void DetectAllCollisions(List<Body> bodies, CollisionFunctor collisionFunctor,
     CollisionSkinPredicate2 collisionPredicate, float collTolerance);

        internal static void CollDetectSphereStaticMeshSweep(BoundingSphere oldSphere, BoundingSphere newSphere, TriangleMesh mesh,
            CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor)
        {
            // really use a swept test - or overlap?
            Vector3 delta = newSphere.Center - oldSphere.Center;
            if (delta.LengthSquared() < (0.25f * newSphere.Radius * newSphere.Radius))
            {
                CollDetectSphereStaticMeshOverlap(oldSphere, newSphere, mesh, info, collTolerance, collisionFunctor);
            }
            else
            {
                Vector3 body0Pos = (info.Skin0.Owner != null) ? info.Skin0.Owner.OldPosition : Vector3.Zero;
                Vector3 body1Pos = (info.Skin1.Owner != null) ? info.Skin1.Owner.OldPosition : Vector3.Zero;

                float sphereTolR = collTolerance + oldSphere.Radius;
                float sphereToR2 = sphereTolR * sphereTolR;

                Vector3 collNormal = Vector3.Zero;

                BoundingBox bb = BoundingBoxHelper.InitialBox;
                BoundingBoxHelper.AddSphere(oldSphere, ref bb);
                BoundingBoxHelper.AddSphere(newSphere, ref bb);

                // get the spheres centers in triangle mesh space
                Vector3 newSphereCen = Vector3.Transform(newSphere.Center, mesh.InverseTransformMatrix);
                Vector3 oldSphereCen = Vector3.Transform(oldSphere.Center, mesh.InverseTransformMatrix);

                unsafe
                {
            #if USE_STACKALLOC
                    SmallCollPointInfo* collPts = stackalloc SmallCollPointInfo[MaxLocalStackSCPI];
                    int* potentialTriangles = stackalloc int[MaxLocalStackTris];
                    {
                        {
            #else
                    SmallCollPointInfo[] collPtArray = SCPIStackAlloc();
                    fixed (SmallCollPointInfo* collPts = collPtArray)
                    {
                        int[] potTriArray = IntStackAlloc();
                        fixed( int* potentialTriangles = potTriArray)
                        {
            #endif
                            int numCollPts = 0;

                            int numTriangles = mesh.GetTrianglesIntersectingtAABox(potentialTriangles, MaxLocalStackTris, ref bb);

                            for (int iTriangle = 0; iTriangle < numTriangles; ++iTriangle)
                            {

                                // first test the old sphere for being on the wrong side
                                IndexedTriangle meshTriangle = mesh.GetTriangle(potentialTriangles[iTriangle]);
                                float distToCentreOld = meshTriangle.Plane.DotCoordinate(oldSphereCen);
                                if (distToCentreOld <= 0.0f)
                                    continue;
                                // now test the new sphere for being clear

                                float distToCentreNew = meshTriangle.Plane.DotCoordinate(newSphereCen);
                                if (distToCentreNew > sphereTolR)
                                    continue;

                                int i0, i1, i2;
                                meshTriangle.GetVertexIndices(out i0, out i1, out i2);

                                Triangle triangle = new Triangle(mesh.GetVertex(i0), mesh.GetVertex(i1), mesh.GetVertex(i2));

                                // If the old sphere is intersecting, just use that result
                                float s, t;
                                float d2 = Distance.PointTriangleDistanceSq(out s, out t, oldSphereCen, triangle);

                                if (d2 < sphereToR2)
                                {
                                    float dist = (float)System.Math.Sqrt(d2);
                                    float depth = oldSphere.Radius - dist;
                                    Vector3 triangleN = triangle.Normal;
                                    Vector3 normSafe = oldSphereCen - triangle.GetPoint(s, t);

                                    JiggleMath.NormalizeSafe(ref normSafe);

                                    Vector3 collisionN = (dist > float.Epsilon) ? normSafe : triangleN;
                                    // since impulse gets applied at the old position
                                    Vector3 pt = oldSphere.Center - oldSphere.Radius * collisionN;
                                    if (numCollPts < MaxLocalStackSCPI)
                                    {
                                        collPts[numCollPts++] = new SmallCollPointInfo(pt - body0Pos, pt - body1Pos, depth);
                                    }
                                    collNormal += collisionN;
                                }
                                else if (distToCentreNew < distToCentreOld)
                                {
                                    // old sphere is not intersecting - do a sweep, but only if the sphere is moving into the
                                    // triangle
                                    Vector3 pt, N; // CHECK THIS
                                    float depth;
                                    if (Intersection.SweptSphereTriangleIntersection(out pt, out N, out depth, oldSphere, newSphere, triangle,
                                        distToCentreOld, distToCentreNew, Intersection.EdgesToTest.EdgeAll, Intersection.CornersToTest.CornerAll))
                                    {
                                        // collision point etc must be relative to the old position because that's
                                        //where the impulses are applied
                                        float dist = (float)System.Math.Sqrt(d2);
                                        float depth2 = oldSphere.Radius - dist;
//.........这里部分代码省略.........

        /// <summary>
        /// CollDetectCapsuleStaticMeshOverlap
        /// </summary>
        /// <param name="oldCapsule"></param>
        /// <param name="newCapsule"></param>
        /// <param name="mesh"></param>
        /// <param name="info"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        private void CollDetectCapsuleStaticMeshOverlap(Capsule oldCapsule, Capsule newCapsule,
            TriangleMesh mesh, CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor)
        {
            Vector3 body0Pos = (info.Skin0.Owner != null) ? info.Skin0.Owner.OldPosition : Vector3.Zero;
            Vector3 body1Pos = (info.Skin1.Owner != null) ? info.Skin1.Owner.OldPosition : Vector3.Zero;

            float capsuleTolR = collTolerance + newCapsule.Radius;
            float capsuleTolR2 = capsuleTolR * capsuleTolR;

            Vector3 collNormal = Vector3.Zero;

            BoundingBox bb = BoundingBoxHelper.InitialBox;
            BoundingBoxHelper.AddCapsule(newCapsule, ref bb);

            unsafe
            {
            #if USE_STACKALLOC
                SmallCollPointInfo* collPts = stackalloc SmallCollPointInfo[MaxLocalStackSCPI];
                int* potentialTriangles = stackalloc int[MaxLocalStackTris];
                {
                    {
            #else
                SmallCollPointInfo[] collPtArray = SCPIStackAlloc();
                fixed (SmallCollPointInfo* collPts = collPtArray)
                {
                    int[] potTriArray = IntStackAlloc();
                    fixed (int* potentialTriangles = potTriArray)
                    {
            #endif
                        int numCollPts = 0;

                        int numTriangles = mesh.GetTrianglesIntersectingtAABox(potentialTriangles, MaxLocalStackTris, ref bb);

                        Vector3 capsuleStart = newCapsule.Position;
                        Vector3 capsuleEnd = newCapsule.GetEnd();
                        Matrix4 meshInvTransform = mesh.InverseTransformMatrix;

                        Vector3 meshSpaceCapsuleStart = Vector3.Transform(capsuleStart, meshInvTransform);
                        Vector3 meshSpaceCapsuleEnd = Vector3.Transform(capsuleEnd, meshInvTransform);

                        for (int iTriangle = 0; iTriangle < numTriangles; ++iTriangle)
                        {
                            IndexedTriangle meshTriangle = mesh.GetTriangle(potentialTriangles[iTriangle]);

                            // we do the plane test using the capsule in mesh space
                            float distToStart = meshTriangle.Plane.DotCoordinate(meshSpaceCapsuleStart);
                            float distToEnd = meshTriangle.Plane.DotCoordinate(meshSpaceCapsuleEnd);

                            // BEN-BUG-FIX: Fixed by replacing 0.0F with -capsuleTolR.
                            if ((distToStart > capsuleTolR && distToEnd > capsuleTolR)
                                || (distToStart < -capsuleTolR && distToEnd < -capsuleTolR))
                                continue;

                            // we now transform the triangle into world space (we could keep leave the mesh alone
                            // but at this point 3 vector transforms is probably not a major slow down)
                            int i0, i1, i2;
                            meshTriangle.GetVertexIndices(out i0, out i1, out i2);

                            Vector3 triVec0;
                            Vector3 triVec1;
                            Vector3 triVec2;
                            mesh.GetVertex(i0, out triVec0);
                            mesh.GetVertex(i1, out triVec1);
                            mesh.GetVertex(i2, out triVec2);

                            // Deano move tri into world space
                            Matrix4 transformMatrix = mesh.TransformMatrix;
                            Vector3.Transform(ref triVec0, ref transformMatrix, out triVec0);
                            Vector3.Transform(ref triVec1, ref transformMatrix, out triVec1);
                            Vector3.Transform(ref triVec2, ref transformMatrix, out triVec2);
                            Triangle triangle = new Triangle(ref triVec0, ref triVec1, ref triVec2);

                            Segment seg = new Segment(capsuleStart, capsuleEnd - capsuleStart);

                            float tS, tT0, tT1;
                            float d2 = Distance.SegmentTriangleDistanceSq(out tS, out tT0, out tT1, seg, triangle);

                            if (d2 < capsuleTolR2)
                            {
                                Vector3 oldCapsuleStart = oldCapsule.Position;
                                Vector3 oldCapsuleEnd = oldCapsule.GetEnd();
                                Segment oldSeg = new Segment(oldCapsuleStart, oldCapsuleEnd - oldCapsuleStart);
                                d2 = Distance.SegmentTriangleDistanceSq(out tS, out tT0, out tT1, oldSeg, triangle);
                                // report result from old position
                                float dist = (float)System.Math.Sqrt(d2);
                                float depth = oldCapsule.Radius - dist;
                                Vector3 pt = triangle.GetPoint(tT0, tT1);
                                Vector3 collisionN = (d2 > JiggleMath.Epsilon) ? JiggleMath.NormalizeSafe(oldSeg.GetPoint(tS) - pt) :
                                    meshTriangle.Plane.Normal;
                                if (numCollPts < MaxLocalStackSCPI)
                                {
//.........这里部分代码省略.........

        /// <summary>
        /// CollDetectSweep
        /// </summary>
        /// <param name="info"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        private void CollDetectSweep(CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor)
        {
            Capsule oldCapsule = info.Skin0.GetPrimitiveOldWorld(info.IndexPrim0) as Capsule;
            Capsule newCapsule = info.Skin0.GetPrimitiveNewWorld(info.IndexPrim0) as Capsule;

            // todo - proper swept test
            // note - mesh is static and its triangles are in world space
            TriangleMesh mesh = info.Skin1.GetPrimitiveNewWorld(info.IndexPrim1) as TriangleMesh;

            CollDetectCapsulseStaticMeshSweep(oldCapsule, newCapsule, mesh, info, collTolerance, collisionFunctor);
        }

        /// <summary>
        /// CollDetectCapsulseStaticMeshSweep
        /// </summary>
        /// <param name="oldCapsule"></param>
        /// <param name="newCapsule"></param>
        /// <param name="mesh"></param>
        /// <param name="info"></param>
        /// <param name="collTolerance"></param>
        /// <param name="collisionFunctor"></param>
        private void CollDetectCapsulseStaticMeshSweep(Capsule oldCapsule, Capsule newCapsule,
            TriangleMesh mesh, CollDetectInfo info, float collTolerance, CollisionFunctor collisionFunctor)
        {
            // really use a swept test - or overlap?
            Vector3 delta = newCapsule.Position - oldCapsule.Position;
            if (delta.LengthSquared < (0.25f * newCapsule.Radius * newCapsule.Radius))
            {
                CollDetectCapsuleStaticMeshOverlap(oldCapsule, newCapsule, mesh, info, collTolerance, collisionFunctor);
            }
            else
            {
                float capsuleLen = oldCapsule.Length;
                float capsuleRadius = oldCapsule.Radius;

                int nSpheres = 2 + (int)(capsuleLen / (2.0f * oldCapsule.Radius));
                for (int iSphere = 0; iSphere < nSpheres; ++iSphere)
                {
                    float offset = ((float)iSphere) * capsuleLen / ((float)nSpheres - 1.0f);
                    BoundingSphere oldSphere = new BoundingSphere(oldCapsule.Position + oldCapsule.Orientation.Backward() * offset, capsuleRadius);
                    BoundingSphere newSphere = new BoundingSphere(newCapsule.Position + newCapsule.Orientation.Backward() * offset, capsuleRadius);
                    CollDetectSphereStaticMesh.CollDetectSphereStaticMeshSweep(oldSphere, newSphere, mesh, info, collTolerance, collisionFunctor);
                }
            }
        }

        /// <summary>
        /// DetectAllCollisions
        /// </summary>
        /// <param name="bodies"></param>
        /// <param name="collisionFunctor"></param>
        /// <param name="collisionPredicate"></param>
        /// <param name="collTolerance"></param>
        public override void DetectAllCollisions(List<Body> bodies, CollisionFunctor collisionFunctor, CollisionSkinPredicate2 collisionPredicate, float collTolerance)
        {
            int numSkins = skins.Count;
            int numBodies = bodies.Count;

            CollDetectInfo info = new CollDetectInfo();

            for (int ibody = 0; ibody < numBodies; ++ibody)
            {
                Body body = bodies[ibody];
                if(!body.IsActive)
                    continue;

                info.Skin0 = body.CollisionSkin;
                if (info.Skin0 == null)
                    continue;

                for (int skin = 0; skin < numSkins; ++skin)
                {
                    info.Skin1 = skins[skin];
                    if (info.Skin0 == info.Skin1)
                        continue;

                    // CHANGE
                    if (info.Skin1 == null)
                        continue;

                    bool skinSleeping = true;

                    if (info.Skin1.Owner != null && info.Skin1.Owner.IsActive)
                        skinSleeping = false;

                    if ((skinSleeping == false) && (info.Skin1.ID < info.Skin0.ID))
                        continue;

                    if((collisionPredicate != null) &&
                        collisionPredicate.ConsiderSkinPair(info.Skin0,info.Skin1) == false)
                    continue;

                    // basic bbox test
                    if(BoundingBoxHelper.OverlapTest(ref info.Skin0.WorldBoundingBox,
                        ref info.Skin1.WorldBoundingBox,collTolerance))
                    {
                        if (CheckCollidables(info.Skin0,info.Skin1))
                        {
                            int bodyPrimitives = info.Skin0.NumPrimitives;
                            int primitves = info.Skin1.NumPrimitives;

                            for(info.IndexPrim0 = 0; info.IndexPrim0 < bodyPrimitives; ++info.IndexPrim0)
                            {
                                for (info.IndexPrim1 = 0; info.IndexPrim1 < primitves; ++info.IndexPrim1)
                                {
                                    DetectFunctor f = GetCollDetectFunctor(info.Skin0.GetPrimitiveNewWorld(info.IndexPrim0).Type,
                                        info.Skin1.GetPrimitiveNewWorld(info.IndexPrim1).Type);
                                    if (f != null)
                                        f.CollDetect(info, collTolerance, collisionFunctor);
                                }
                            }
                        }
                    } // overlapt test
                } // loop over skins
            } // loop over bodies
        }