Ejemplo n.º 1
0
        public static List<Fixture> AttachCompoundPolygon(List<Vertices> list, float density, PhysicsBody body, object userData)
        {
            List<Fixture> res = new List<Fixture>(list.Count);

            //Then we create several fixtures using the body
            foreach (Vertices vertices in list)
            {
                if (vertices.Count == 2)
                {
                    EdgeShape shape = new EdgeShape(vertices[0], vertices[1]);
                    res.Add(body.CreateFixture(shape, userData));
                }
                else
                {
                    PolygonShape shape = new PolygonShape(vertices, density);
                    res.Add(body.CreateFixture(shape, userData));
                }
            }

            return res;
        }
Ejemplo n.º 2
0
 public static Fixture AttachEdge(Vector2 start, Vector2 end, PhysicsBody body, object userData)
 {
     EdgeShape edgeShape = new EdgeShape(start, end);
     return body.CreateFixture(edgeShape, userData);
 }
Ejemplo n.º 3
0
        /// <summary>
        /// Get a child edge.
        /// </summary>
        /// <param name="edge">The edge.</param>
        /// <param name="index">The index.</param>
        public void GetChildEdge(ref EdgeShape edge, int index)
        {
            Debug.Assert(2 <= Vertices.Count);
            Debug.Assert(0 <= index && index < Vertices.Count);
            edge.ShapeType = ShapeType.Edge;
            edge._radius = _radius;
            edge.HasVertex0 = true;
            edge.HasVertex3 = true;

            int i0 = index - 1 >= 0 ? index - 1 : Vertices.Count - 1;
            int i1 = index;
            int i2 = index + 1 < Vertices.Count ? index + 1 : 0;
            int i3 = index + 2;
            while (i3 >= Vertices.Count)
            {
                i3 -= Vertices.Count;
            }

            edge.Vertex0 = Vertices[i0];
            edge.Vertex1 = Vertices[i1];
            edge.Vertex2 = Vertices[i2];
            edge.Vertex3 = Vertices[i3];
        }
Ejemplo n.º 4
0
 public bool CompareTo(EdgeShape shape)
 {
     return (HasVertex0 == shape.HasVertex0 &&
             HasVertex3 == shape.HasVertex3 &&
             Vertex0 == shape.Vertex0 &&
             Vertex1 == shape.Vertex1 &&
             Vertex2 == shape.Vertex2 &&
             Vertex3 == shape.Vertex3);
 }
Ejemplo n.º 5
0
 public override Shape Clone()
 {
     EdgeShape edge = new EdgeShape();
     edge._radius = _radius;
     edge._density = _density;
     edge.HasVertex0 = HasVertex0;
     edge.HasVertex3 = HasVertex3;
     edge.Vertex0 = Vertex0;
     edge._vertex1 = _vertex1;
     edge._vertex2 = _vertex2;
     edge.Vertex3 = Vertex3;
     edge.MassData = MassData;
     return edge;
 }
Ejemplo n.º 6
0
        /// <summary>
        /// Collides and edge and a polygon, taking into account edge adjacency.
        /// </summary>
        /// <param name="manifold">The manifold.</param>
        /// <param name="edgeA">The edge A.</param>
        /// <param name="xfA">The xf A.</param>
        /// <param name="polygonB">The polygon B.</param>
        /// <param name="xfB">The xf B.</param>
        public static void CollideEdgeAndPolygon(ref Manifold manifold,
                                                 EdgeShape edgeA, ref Transform xfA,
                                                 PolygonShape polygonB, ref Transform xfB)
        {
            MathUtils.MultiplyT(ref xfA, ref xfB, out _xf);

            // Edge geometry
            _edgeA.V0 = edgeA.Vertex0;
            _edgeA.V1 = edgeA.Vertex1;
            _edgeA.V2 = edgeA.Vertex2;
            _edgeA.V3 = edgeA.Vertex3;
            Vector2 e = _edgeA.V2 - _edgeA.V1;

            // Normal points outwards in CCW order.
            _edgeA.Normal = new Vector2(e.Y, -e.X);
            _edgeA.Normal.Normalize();
            _edgeA.HasVertex0 = edgeA.HasVertex0;
            _edgeA.HasVertex3 = edgeA.HasVertex3;

            // Proxy for edge
            _proxyA.Vertices[0] = _edgeA.V1;
            _proxyA.Vertices[1] = _edgeA.V2;
            _proxyA.Normals[0] = _edgeA.Normal;
            _proxyA.Normals[1] = -_edgeA.Normal;
            _proxyA.Centroid = 0.5f * (_edgeA.V1 + _edgeA.V2);
            _proxyA.Count = 2;

            // Proxy for polygon
            _proxyB.Count = polygonB.Vertices.Count;
            _proxyB.Centroid = MathUtils.Multiply(ref _xf, ref polygonB.MassData.Centroid);
            for (int i = 0; i < polygonB.Vertices.Count; ++i)
            {
                _proxyB.Vertices[i] = MathUtils.Multiply(ref _xf, polygonB.Vertices[i]);
                _proxyB.Normals[i] = MathUtils.Multiply(ref _xf.R, polygonB.Normals[i]);
            }

            _radius = 2.0f * Settings.PolygonRadius;

            _limit11 = Vector2.Zero;
            _limit12 = Vector2.Zero;
            _limit21 = Vector2.Zero;
            _limit22 = Vector2.Zero;

            //Collide(ref manifold); inline start
            manifold.PointCount = 0;

            //ComputeAdjacency(); inline start
            Vector2 v0 = _edgeA.V0;
            Vector2 v1 = _edgeA.V1;
            Vector2 v2 = _edgeA.V2;
            Vector2 v3 = _edgeA.V3;

            // Determine allowable the normal regions based on adjacency.
            // Note: it may be possible that no normal is admissable.
            Vector2 centerB = _proxyB.Centroid;
            if (_edgeA.HasVertex0)
            {
                Vector2 e0 = v1 - v0;
                Vector2 e1 = v2 - v1;
                Vector2 n0 = new Vector2(e0.Y, -e0.X);
                Vector2 n1 = new Vector2(e1.Y, -e1.X);
                n0.Normalize();
                n1.Normalize();

                bool convex = MathUtils.Cross(n0, n1) >= 0.0f;
                bool front0 = Vector2.Dot(n0, centerB - v0) >= 0.0f;
                bool front1 = Vector2.Dot(n1, centerB - v1) >= 0.0f;

                if (convex)
                {
                    if (front0 || front1)
                    {
                        _limit11 = n1;
                        _limit12 = n0;
                    }
                    else
                    {
                        _limit11 = -n1;
                        _limit12 = -n0;
                    }
                }
                else
                {
                    if (front0 && front1)
                    {
                        _limit11 = n0;
                        _limit12 = n1;
                    }
                    else
                    {
                        _limit11 = -n0;
                        _limit12 = -n1;
                    }
                }
            }
            else
            {
                _limit11 = Vector2.Zero;
                _limit12 = Vector2.Zero;
            }

            if (_edgeA.HasVertex3)
            {
                Vector2 e1 = v2 - v1;
                Vector2 e2 = v3 - v2;
                Vector2 n1 = new Vector2(e1.Y, -e1.X);
                Vector2 n2 = new Vector2(e2.Y, -e2.X);
                n1.Normalize();
                n2.Normalize();

                bool convex = MathUtils.Cross(n1, n2) >= 0.0f;
                bool front1 = Vector2.Dot(n1, centerB - v1) >= 0.0f;
                bool front2 = Vector2.Dot(n2, centerB - v2) >= 0.0f;

                if (convex)
                {
                    if (front1 || front2)
                    {
                        _limit21 = n2;
                        _limit22 = n1;
                    }
                    else
                    {
                        _limit21 = -n2;
                        _limit22 = -n1;
                    }
                }
                else
                {
                    if (front1 && front2)
                    {
                        _limit21 = n1;
                        _limit22 = n2;
                    }
                    else
                    {
                        _limit21 = -n1;
                        _limit22 = -n2;
                    }
                }
            }
            else
            {
                _limit21 = Vector2.Zero;
                _limit22 = Vector2.Zero;
            }

            //ComputeAdjacency(); inline end

            //EPAxis edgeAxis = ComputeEdgeSeparation(); inline start
            EPAxis edgeAxis = ComputeEdgeSeparation();

            // If no valid normal can be found than this edge should not collide.
            // This can happen on the middle edge of a 3-edge zig-zag chain.
            if (edgeAxis.Type == EPAxisType.Unknown)
            {
                return;
            }

            if (edgeAxis.Separation > _radius)
            {
                return;
            }

            EPAxis polygonAxis = ComputePolygonSeparation();
            if (polygonAxis.Type != EPAxisType.Unknown && polygonAxis.Separation > _radius)
            {
                return;
            }

            // Use hysteresis for jitter reduction.
            const float k_relativeTol = 0.98f;
            const float k_absoluteTol = 0.001f;

            EPAxis primaryAxis;
            if (polygonAxis.Type == EPAxisType.Unknown)
            {
                primaryAxis = edgeAxis;
            }
            else if (polygonAxis.Separation > k_relativeTol * edgeAxis.Separation + k_absoluteTol)
            {
                primaryAxis = polygonAxis;
            }
            else
            {
                primaryAxis = edgeAxis;
            }

            EPProxy proxy1;
            EPProxy proxy2;
            FixedArray2<ClipVertex> incidentEdge = new FixedArray2<ClipVertex>();
            if (primaryAxis.Type == EPAxisType.EdgeA)
            {
                proxy1 = _proxyA;
                proxy2 = _proxyB;
                manifold.Type = ManifoldType.FaceA;
            }
            else
            {
                proxy1 = _proxyB;
                proxy2 = _proxyA;
                manifold.Type = ManifoldType.FaceB;
            }

            int edge1 = primaryAxis.Index;

            FindIncidentEdge(ref incidentEdge, proxy1, primaryAxis.Index, proxy2);
            int count1 = proxy1.Count;

            int iv1 = edge1;
            int iv2 = edge1 + 1 < count1 ? edge1 + 1 : 0;

            Vector2 v11 = proxy1.Vertices[iv1];
            Vector2 v12 = proxy1.Vertices[iv2];

            Vector2 tangent = v12 - v11;
            tangent.Normalize();

            Vector2 normal = MathUtils.Cross(tangent, 1.0f);
            Vector2 planePoint = 0.5f * (v11 + v12);

            // Face offset.
            float frontOffset = Vector2.Dot(normal, v11);

            // Side offsets, extended by polytope skin thickness.
            float sideOffset1 = -Vector2.Dot(tangent, v11) + _radius;
            float sideOffset2 = Vector2.Dot(tangent, v12) + _radius;

            // Clip incident edge against extruded edge1 side edges.
            FixedArray2<ClipVertex> clipPoints1;
            FixedArray2<ClipVertex> clipPoints2;
            int np;

            // Clip to box side 1
            np = ClipSegmentToLine(out clipPoints1, ref incidentEdge, -tangent, sideOffset1, iv1);

            if (np < Settings.MaxManifoldPoints)
            {
                return;
            }

            // Clip to negative box side 1
            np = ClipSegmentToLine(out clipPoints2, ref clipPoints1, tangent, sideOffset2, iv2);

            if (np < Settings.MaxManifoldPoints)
            {
                return;
            }

            // Now clipPoints2 contains the clipped points.
            if (primaryAxis.Type == EPAxisType.EdgeA)
            {
                manifold.LocalNormal = normal;
                manifold.LocalPoint = planePoint;
            }
            else
            {
                manifold.LocalNormal = MathUtils.MultiplyT(ref _xf.R, ref normal);
                manifold.LocalPoint = MathUtils.MultiplyT(ref _xf, ref planePoint);
            }

            int pointCount = 0;
            for (int i1 = 0; i1 < Settings.MaxManifoldPoints; ++i1)
            {
                float separation = Vector2.Dot(normal, clipPoints2[i1].V) - frontOffset;

                if (separation <= _radius)
                {
                    ManifoldPoint cp = manifold.Points[pointCount];

                    if (primaryAxis.Type == EPAxisType.EdgeA)
                    {
                        cp.LocalPoint = MathUtils.MultiplyT(ref _xf, clipPoints2[i1].V);
                        cp.Id = clipPoints2[i1].ID;
                    }
                    else
                    {
                        cp.LocalPoint = clipPoints2[i1].V;
                        cp.Id.Features.TypeA = clipPoints2[i1].ID.Features.TypeB;
                        cp.Id.Features.TypeB = clipPoints2[i1].ID.Features.TypeA;
                        cp.Id.Features.IndexA = clipPoints2[i1].ID.Features.IndexB;
                        cp.Id.Features.IndexB = clipPoints2[i1].ID.Features.IndexA;
                    }

                    manifold.Points[pointCount] = cp;

                    ++pointCount;
                }
            }

            manifold.PointCount = pointCount;

            //Collide(ref manifold); inline end
        }
Ejemplo n.º 7
0
        /// <summary>
        /// Compute contact points for edge versus circle.
        /// This accounts for edge connectivity.
        /// </summary>
        /// <param name="manifold">The manifold.</param>
        /// <param name="edgeA">The edge A.</param>
        /// <param name="transformA">The transform A.</param>
        /// <param name="circleB">The circle B.</param>
        /// <param name="transformB">The transform B.</param>
        public static void CollideEdgeAndCircle(ref Manifold manifold,
                                                EdgeShape edgeA, ref Transform transformA,
                                                CircleShape circleB, ref Transform transformB)
        {
            manifold.PointCount = 0;

            // Compute circle in frame of edge
            Vector2 Q = MathUtils.MultiplyT(ref transformA, MathUtils.Multiply(ref transformB, ref circleB._position));

            Vector2 A = edgeA.Vertex1, B = edgeA.Vertex2;
            Vector2 e = B - A;

            // Barycentric coordinates
            float u = Vector2.Dot(e, B - Q);
            float v = Vector2.Dot(e, Q - A);

            float radius = edgeA.Radius + circleB.Radius;

            ContactFeature cf;
            cf.IndexB = 0;
            cf.TypeB = (byte)ContactFeatureType.Vertex;

            Vector2 P, d;

            // Region A
            if (v <= 0.0f)
            {
                P = A;
                d = Q - P;
                float dd;
                Vector2.Dot(ref d, ref d, out dd);
                if (dd > radius * radius)
                {
                    return;
                }

                // Is there an edge connected to A?
                if (edgeA.HasVertex0)
                {
                    Vector2 A1 = edgeA.Vertex0;
                    Vector2 B1 = A;
                    Vector2 e1 = B1 - A1;
                    float u1 = Vector2.Dot(e1, B1 - Q);

                    // Is the circle in Region AB of the previous edge?
                    if (u1 > 0.0f)
                    {
                        return;
                    }
                }

                cf.IndexA = 0;
                cf.TypeA = (byte)ContactFeatureType.Vertex;
                manifold.PointCount = 1;
                manifold.Type = ManifoldType.Circles;
                manifold.LocalNormal = Vector2.Zero;
                manifold.LocalPoint = P;
                ManifoldPoint mp = new ManifoldPoint();
                mp.Id.Key = 0;
                mp.Id.Features = cf;
                mp.LocalPoint = circleB.Position;
                manifold.Points[0] = mp;
                return;
            }

            // Region B
            if (u <= 0.0f)
            {
                P = B;
                d = Q - P;
                float dd;
                Vector2.Dot(ref d, ref d, out dd);
                if (dd > radius * radius)
                {
                    return;
                }

                // Is there an edge connected to B?
                if (edgeA.HasVertex3)
                {
                    Vector2 B2 = edgeA.Vertex3;
                    Vector2 A2 = B;
                    Vector2 e2 = B2 - A2;
                    float v2 = Vector2.Dot(e2, Q - A2);

                    // Is the circle in Region AB of the next edge?
                    if (v2 > 0.0f)
                    {
                        return;
                    }
                }

                cf.IndexA = 1;
                cf.TypeA = (byte)ContactFeatureType.Vertex;
                manifold.PointCount = 1;
                manifold.Type = ManifoldType.Circles;
                manifold.LocalNormal = Vector2.Zero;
                manifold.LocalPoint = P;
                ManifoldPoint mp = new ManifoldPoint();
                mp.Id.Key = 0;
                mp.Id.Features = cf;
                mp.LocalPoint = circleB.Position;
                manifold.Points[0] = mp;
                return;
            }

            // Region AB
            float den;
            Vector2.Dot(ref e, ref e, out den);
            Debug.Assert(den > 0.0f);
            P = (1.0f / den) * (u * A + v * B);
            d = Q - P;
            float dd2;
            Vector2.Dot(ref d, ref d, out dd2);
            if (dd2 > radius * radius)
            {
                return;
            }

            Vector2 n = new Vector2(-e.Y, e.X);
            if (Vector2.Dot(n, Q - A) < 0.0f)
            {
                n = new Vector2(-n.X, -n.Y);
            }
            n.Normalize();

            cf.IndexA = 0;
            cf.TypeA = (byte)ContactFeatureType.Face;
            manifold.PointCount = 1;
            manifold.Type = ManifoldType.FaceA;
            manifold.LocalNormal = n;
            manifold.LocalPoint = A;
            ManifoldPoint mp2 = new ManifoldPoint();
            mp2.Id.Key = 0;
            mp2.Id.Features = cf;
            mp2.LocalPoint = circleB.Position;
            manifold.Points[0] = mp2;
        }
Ejemplo n.º 8
0
        public void Deserialize(PhysicsWorld world, Stream stream)
        {
            world.Clear();

            XMLFragmentElement root = XMLFragmentParser.LoadFromStream(stream);

            if (root.Name.ToLower() != "world")
                throw new Exception();

            foreach (XMLFragmentElement main in root.Elements)
            {
                if (main.Name.ToLower() == "gravity")
                {
                    world.Gravity = ReadVector(main);
                }
            }

            foreach (XMLFragmentElement shapeElement in root.Elements)
            {
                if (shapeElement.Name.ToLower() == "shapes")
                {
                    foreach (XMLFragmentElement n in shapeElement.Elements)
                    {
                        if (n.Name.ToLower() != "shape")
                            throw new Exception();

                        ShapeType type = (ShapeType)Enum.Parse(typeof(ShapeType), n.Attributes[0].Value, true);

                        switch (type)
                        {
                            case ShapeType.Circle:
                                {
                                    CircleShape shape = new CircleShape();

                                    foreach (XMLFragmentElement sn in n.Elements)
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "radius":
                                                shape.Radius = float.Parse(sn.Value);
                                                break;

                                            case "position":
                                                shape.Position = ReadVector(sn);
                                                break;

                                            default:
                                                throw new Exception();
                                        }
                                    }

                                    _shapes.Add(shape);
                                }
                                break;

                            case ShapeType.Polygon:
                                {
                                    PolygonShape shape = new PolygonShape();

                                    foreach (XMLFragmentElement sn in n.Elements)
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "vertices":
                                                {
                                                    List<Vector2> verts = new List<Vector2>();

                                                    foreach (XMLFragmentElement vert in sn.Elements)
                                                        verts.Add(ReadVector(vert));

                                                    shape.Set(new Vertices(verts.ToArray()));
                                                }
                                                break;

                                            case "centroid":
                                                shape.MassData.Centroid = ReadVector(sn);
                                                break;
                                        }
                                    }

                                    _shapes.Add(shape);
                                }
                                break;

                            case ShapeType.Edge:
                                {
                                    EdgeShape shape = new EdgeShape();
                                    foreach (XMLFragmentElement sn in n.Elements)
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "hasvertex0":
                                                shape.HasVertex0 = bool.Parse(sn.Value);
                                                break;

                                            case "hasvertex3":
                                                shape.HasVertex0 = bool.Parse(sn.Value);
                                                break;

                                            case "vertex0":
                                                shape.Vertex0 = ReadVector(sn);
                                                break;

                                            case "vertex1":
                                                shape.Vertex1 = ReadVector(sn);
                                                break;

                                            case "vertex2":
                                                shape.Vertex2 = ReadVector(sn);
                                                break;

                                            case "vertex3":
                                                shape.Vertex3 = ReadVector(sn);
                                                break;

                                            default:
                                                throw new Exception();
                                        }
                                    }
                                    _shapes.Add(shape);
                                }
                                break;
                        }
                    }
                }
            }

            foreach (XMLFragmentElement fixtureElement in root.Elements)
            {
                if (fixtureElement.Name.ToLower() == "fixtures")
                {
                    foreach (XMLFragmentElement n in fixtureElement.Elements)
                    {
                        Fixture fixture = new Fixture();

                        if (n.Name.ToLower() != "fixture")
                            throw new Exception();

                        foreach (XMLFragmentElement sn in n.Elements)
                        {
                            switch (sn.Name.ToLower())
                            {
                                case "shape":
                                    fixture.Shape = _shapes[int.Parse(sn.Value)];
                                    break;

                                case "density":
                                    fixture.Shape.Density = float.Parse(sn.Value);
                                    break;

                                case "filterdata":
                                    foreach (XMLFragmentElement ssn in sn.Elements)
                                    {
                                        switch (ssn.Name.ToLower())
                                        {
                                            case "categorybits":
                                                fixture._collisionCategories = (Category)int.Parse(ssn.Value);
                                                break;

                                            case "maskbits":
                                                fixture._collidesWith = (Category)int.Parse(ssn.Value);
                                                break;

                                            case "groupindex":
                                                fixture._collisionGroup = short.Parse(ssn.Value);
                                                break;
                                        }
                                    }

                                    break;

                                case "friction":
                                    fixture.Friction = float.Parse(sn.Value);
                                    break;

                                case "issensor":
                                    fixture.IsSensor = bool.Parse(sn.Value);
                                    break;

                                case "restitution":
                                    fixture.Restitution = float.Parse(sn.Value);
                                    break;

                                case "userdata":
                                    fixture.UserData = ReadSimpleType(sn, null, false);
                                    break;
                            }
                        }

                        _fixtures.Add(fixture);
                    }
                }
            }

            foreach (XMLFragmentElement bodyElement in root.Elements)
            {
                if (bodyElement.Name.ToLower() == "bodies")
                {
                    foreach (XMLFragmentElement n in bodyElement.Elements)
                    {
                        PhysicsBody body = new PhysicsBody(world);

                        if (n.Name.ToLower() != "body")
                            throw new Exception();

                        body.BodyType = (BodyType)Enum.Parse(typeof(BodyType), n.Attributes[0].Value, true);

                        foreach (XMLFragmentElement sn in n.Elements)
                        {
                            switch (sn.Name.ToLower())
                            {
                                case "active":
                                    if (bool.Parse(sn.Value))
                                        body.Flags |= BodyFlags.Enabled;
                                    else
                                        body.Flags &= ~BodyFlags.Enabled;
                                    break;

                                case "allowsleep":
                                    body.SleepingAllowed = bool.Parse(sn.Value);
                                    break;

                                case "angle":
                                    {
                                        Vector2 position = body.Position;
                                        body.SetTransformIgnoreContacts(ref position, float.Parse(sn.Value));
                                    }
                                    break;

                                case "angulardamping":
                                    body.AngularDamping = float.Parse(sn.Value);
                                    break;

                                case "angularvelocity":
                                    body.AngularVelocity = float.Parse(sn.Value);
                                    break;

                                case "awake":
                                    body.Awake = bool.Parse(sn.Value);
                                    break;

                                case "bullet":
                                    body.IsBullet = bool.Parse(sn.Value);
                                    break;

                                case "fixedrotation":
                                    body.FixedRotation = bool.Parse(sn.Value);
                                    break;

                                case "lineardamping":
                                    body.LinearDamping = float.Parse(sn.Value);
                                    break;

                                case "linearvelocity":
                                    body.LinearVelocity = ReadVector(sn);
                                    break;

                                case "position":
                                    {
                                        float rotation = body.Rotation;
                                        Vector2 position = ReadVector(sn);
                                        body.SetTransformIgnoreContacts(ref position, rotation);
                                    }
                                    break;

                                case "userdata":
                                    body.UserData = ReadSimpleType(sn, null, false);
                                    break;

                                case "fixtures":
                                    {
                                        foreach (XMLFragmentElement v in sn.Elements)
                                        {
                                            Fixture blueprint = _fixtures[int.Parse(v.Value)];
                                            Fixture f = new Fixture(body, blueprint.Shape);
                                            f.Restitution = blueprint.Restitution;
                                            f.UserData = blueprint.UserData;
                                            f.Friction = blueprint.Friction;
                                            f.CollidesWith = blueprint.CollidesWith;
                                            f.CollisionCategories = blueprint.CollisionCategories;
                                            f.CollisionGroup = blueprint.CollisionGroup;
                                        }
                                        break;
                                    }
                            }
                        }

                        _bodies.Add(body);
                    }
                }
            }

            foreach (XMLFragmentElement jointElement in root.Elements)
            {
                if (jointElement.Name.ToLower() == "joints")
                {
                    foreach (XMLFragmentElement n in jointElement.Elements)
                    {
                        PhysicsJoint joint;

                        if (n.Name.ToLower() != "joint")
                            throw new Exception();

                        JointType type = (JointType)Enum.Parse(typeof(JointType), n.Attributes[0].Value, true);

                        int bodyAIndex = -1, bodyBIndex = -1;
                        bool collideConnected = false;
                        object userData = null;

                        foreach (XMLFragmentElement sn in n.Elements)
                        {
                            switch (sn.Name.ToLower())
                            {
                                case "bodya":
                                    bodyAIndex = int.Parse(sn.Value);
                                    break;

                                case "bodyb":
                                    bodyBIndex = int.Parse(sn.Value);
                                    break;

                                case "collideconnected":
                                    collideConnected = bool.Parse(sn.Value);
                                    break;

                                case "userdata":
                                    userData = ReadSimpleType(sn, null, false);
                                    break;
                            }
                        }

                        PhysicsBody bodyA = _bodies[bodyAIndex];
                        PhysicsBody bodyB = _bodies[bodyBIndex];

                        switch (type)
                        {
                            case JointType.Distance:
                                joint = new DistanceJoint();
                                break;

                            case JointType.Friction:
                                joint = new FrictionJoint();
                                break;

                            case JointType.Line:
                                joint = new LineJoint();
                                break;

                            case JointType.Prismatic:
                                joint = new PrismaticJoint();
                                break;

                            case JointType.Pulley:
                                joint = new PulleyJoint();
                                break;

                            case JointType.Revolute:
                                joint = new RevoluteJoint();
                                break;

                            case JointType.Weld:
                                joint = new WeldJoint();
                                break;

                            case JointType.Rope:
                                joint = new RopeJoint();
                                break;

                            case JointType.Angle:
                                joint = new AngleJoint();
                                break;

                            case JointType.Slider:
                                joint = new SliderJoint();
                                break;

                            case JointType.Gear:
                                throw new Exception("GearJoint is not supported.");
                            default:
                                throw new Exception("Invalid or unsupported joint.");
                        }

                        joint.CollideConnected = collideConnected;
                        joint.UserData = userData;
                        joint.BodyA = bodyA;
                        joint.BodyB = bodyB;
                        _joints.Add(joint);
                        world.AddJoint(joint);

                        foreach (XMLFragmentElement sn in n.Elements)
                        {
                            // check for specific nodes
                            switch (type)
                            {
                                case JointType.Distance:
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "dampingratio":
                                                ((DistanceJoint)joint).DampingRatio = float.Parse(sn.Value);
                                                break;

                                            case "frequencyhz":
                                                ((DistanceJoint)joint).Frequency = float.Parse(sn.Value);
                                                break;

                                            case "length":
                                                ((DistanceJoint)joint).Length = float.Parse(sn.Value);
                                                break;

                                            case "localanchora":
                                                ((DistanceJoint)joint).LocalAnchorA = ReadVector(sn);
                                                break;

                                            case "localanchorb":
                                                ((DistanceJoint)joint).LocalAnchorB = ReadVector(sn);
                                                break;
                                        }
                                    }
                                    break;

                                case JointType.Friction:
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "localanchora":
                                                ((FrictionJoint)joint).LocalAnchorA = ReadVector(sn);
                                                break;

                                            case "localanchorb":
                                                ((FrictionJoint)joint).LocalAnchorB = ReadVector(sn);
                                                break;

                                            case "maxforce":
                                                ((FrictionJoint)joint).MaxForce = float.Parse(sn.Value);
                                                break;

                                            case "maxtorque":
                                                ((FrictionJoint)joint).MaxTorque = float.Parse(sn.Value);
                                                break;
                                        }
                                    }
                                    break;

                                case JointType.Line:
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "enablemotor":
                                                ((LineJoint)joint).MotorEnabled = bool.Parse(sn.Value);
                                                break;

                                            case "localanchora":
                                                ((LineJoint)joint).LocalAnchorA = ReadVector(sn);
                                                break;

                                            case "localanchorb":
                                                ((LineJoint)joint).LocalAnchorB = ReadVector(sn);
                                                break;

                                            case "motorspeed":
                                                ((LineJoint)joint).MotorSpeed = float.Parse(sn.Value);
                                                break;

                                            case "dampingratio":
                                                ((LineJoint)joint).DampingRatio = float.Parse(sn.Value);
                                                break;

                                            case "maxmotortorque":
                                                ((LineJoint)joint).MaxMotorTorque = float.Parse(sn.Value);
                                                break;

                                            case "frequencyhz":
                                                ((LineJoint)joint).Frequency = float.Parse(sn.Value);
                                                break;

                                            case "localxaxis":
                                                ((LineJoint)joint).LocalXAxis = ReadVector(sn);
                                                break;
                                        }
                                    }
                                    break;

                                case JointType.Prismatic:
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "enablelimit":
                                                ((PrismaticJoint)joint).LimitEnabled = bool.Parse(sn.Value);
                                                break;

                                            case "enablemotor":
                                                ((PrismaticJoint)joint).MotorEnabled = bool.Parse(sn.Value);
                                                break;

                                            case "localanchora":
                                                ((PrismaticJoint)joint).LocalAnchorA = ReadVector(sn);
                                                break;

                                            case "localanchorb":
                                                ((PrismaticJoint)joint).LocalAnchorB = ReadVector(sn);
                                                break;

                                            case "local1axis1":
                                                ((PrismaticJoint)joint).LocalXAxis1 = ReadVector(sn);
                                                break;

                                            case "maxmotorforce":
                                                ((PrismaticJoint)joint).MaxMotorForce = float.Parse(sn.Value);
                                                break;

                                            case "motorspeed":
                                                ((PrismaticJoint)joint).MotorSpeed = float.Parse(sn.Value);
                                                break;

                                            case "lowertranslation":
                                                ((PrismaticJoint)joint).LowerLimit = float.Parse(sn.Value);
                                                break;

                                            case "uppertranslation":
                                                ((PrismaticJoint)joint).UpperLimit = float.Parse(sn.Value);
                                                break;

                                            case "referenceangle":
                                                ((PrismaticJoint)joint).ReferenceAngle = float.Parse(sn.Value);
                                                break;
                                        }
                                    }
                                    break;

                                case JointType.Pulley:
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "groundanchora":
                                                ((PulleyJoint)joint).GroundAnchorA = ReadVector(sn);
                                                break;

                                            case "groundanchorb":
                                                ((PulleyJoint)joint).GroundAnchorB = ReadVector(sn);
                                                break;

                                            case "lengtha":
                                                ((PulleyJoint)joint).LengthA = float.Parse(sn.Value);
                                                break;

                                            case "lengthb":
                                                ((PulleyJoint)joint).LengthB = float.Parse(sn.Value);
                                                break;

                                            case "localanchora":
                                                ((PulleyJoint)joint).LocalAnchorA = ReadVector(sn);
                                                break;

                                            case "localanchorb":
                                                ((PulleyJoint)joint).LocalAnchorB = ReadVector(sn);
                                                break;

                                            case "maxlengtha":
                                                ((PulleyJoint)joint).MaxLengthA = float.Parse(sn.Value);
                                                break;

                                            case "maxlengthb":
                                                ((PulleyJoint)joint).MaxLengthB = float.Parse(sn.Value);
                                                break;

                                            case "ratio":
                                                ((PulleyJoint)joint).Ratio = float.Parse(sn.Value);
                                                break;
                                        }
                                    }
                                    break;

                                case JointType.Revolute:
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "enablelimit":
                                                ((RevoluteJoint)joint).LimitEnabled = bool.Parse(sn.Value);
                                                break;

                                            case "enablemotor":
                                                ((RevoluteJoint)joint).MotorEnabled = bool.Parse(sn.Value);
                                                break;

                                            case "localanchora":
                                                ((RevoluteJoint)joint).LocalAnchorA = ReadVector(sn);
                                                break;

                                            case "localanchorb":
                                                ((RevoluteJoint)joint).LocalAnchorB = ReadVector(sn);
                                                break;

                                            case "maxmotortorque":
                                                ((RevoluteJoint)joint).MaxMotorTorque = float.Parse(sn.Value);
                                                break;

                                            case "motorspeed":
                                                ((RevoluteJoint)joint).MotorSpeed = float.Parse(sn.Value);
                                                break;

                                            case "lowerangle":
                                                ((RevoluteJoint)joint).LowerLimit = float.Parse(sn.Value);
                                                break;

                                            case "upperangle":
                                                ((RevoluteJoint)joint).UpperLimit = float.Parse(sn.Value);
                                                break;

                                            case "referenceangle":
                                                ((RevoluteJoint)joint).ReferenceAngle = float.Parse(sn.Value);
                                                break;
                                        }
                                    }
                                    break;

                                case JointType.Weld:
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "localanchora":
                                                ((WeldJoint)joint).LocalAnchorA = ReadVector(sn);
                                                break;

                                            case "localanchorb":
                                                ((WeldJoint)joint).LocalAnchorB = ReadVector(sn);
                                                break;
                                        }
                                    }
                                    break;

                                case JointType.Rope:
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "localanchora":
                                                ((RopeJoint)joint).LocalAnchorA = ReadVector(sn);
                                                break;

                                            case "localanchorb":
                                                ((RopeJoint)joint).LocalAnchorB = ReadVector(sn);
                                                break;

                                            case "maxlength":
                                                ((RopeJoint)joint).MaxLength = float.Parse(sn.Value);
                                                break;
                                        }
                                    }
                                    break;

                                case JointType.Gear:
                                    throw new Exception("Gear joint is unsupported");
                                case JointType.Angle:
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "biasfactor":
                                                ((AngleJoint)joint).BiasFactor = float.Parse(sn.Value);
                                                break;

                                            case "maximpulse":
                                                ((AngleJoint)joint).MaxImpulse = float.Parse(sn.Value);
                                                break;

                                            case "softness":
                                                ((AngleJoint)joint).Softness = float.Parse(sn.Value);
                                                break;

                                            case "targetangle":
                                                ((AngleJoint)joint).TargetAngle = float.Parse(sn.Value);
                                                break;
                                        }
                                    }
                                    break;

                                case JointType.Slider:
                                    {
                                        switch (sn.Name.ToLower())
                                        {
                                            case "dampingratio":
                                                ((SliderJoint)joint).DampingRatio = float.Parse(sn.Value);
                                                break;

                                            case "frequencyhz":
                                                ((SliderJoint)joint).Frequency = float.Parse(sn.Value);
                                                break;

                                            case "maxlength":
                                                ((SliderJoint)joint).MaxLength = float.Parse(sn.Value);
                                                break;

                                            case "minlength":
                                                ((SliderJoint)joint).MinLength = float.Parse(sn.Value);
                                                break;

                                            case "localanchora":
                                                ((SliderJoint)joint).LocalAnchorA = ReadVector(sn);
                                                break;

                                            case "localanchorb":
                                                ((SliderJoint)joint).LocalAnchorB = ReadVector(sn);
                                                break;
                                        }
                                    }
                                    break;
                            }
                        }
                    }
                }
            }
        }