public override void StartFrame(ref Microsoft.Xna.Framework.Matrix view, ref Microsoft.Xna.Framework.Matrix projection, Microsoft.Xna.Framework.BoundingFrustum frustrum)
        {
            rend = 0;
            MaterialSortedObjects.Clear();
            
            Vector3[] corners = new Vector3[8];
            frustrum.GetCorners(corners);            
            List<I2DPhysicObject> objs = world.PhysicWorld.TestAABB(new Vector2(corners[0].X, corners[0].Y), new Vector2(corners[2].X, corners[2].Y));

            foreach (var item in objs)
            {
                I2DObject obj = item.Owner;
                if (!MaterialSortedObjects.ContainsKey(obj.Material.GetType()))
                {
                    MaterialSortedObjects[obj.Material.GetType()] = new List<I2DObject>();
                }                

                MaterialSortedObjects[obj.Material.GetType()].Add(obj);
                rend++;
            }

            foreach (var obj  in ghosts)
            {
                if (!MaterialSortedObjects.ContainsKey(obj.Material.GetType()))
                {
                    MaterialSortedObjects[obj.Material.GetType()] = new List<I2DObject>();
                }
                MaterialSortedObjects[obj.Material.GetType()].Add(obj);                
            }
            rend += ghosts.Count;
        }
        public override void DoPreFrameWork(Microsoft.Xna.Framework.BoundingFrustum frustum)
        {
            Vector3[] corners = frustum.GetCorners();

            float xx = corners[6].X - corners[2].X;
            float yy = corners[2].Y - corners[6].Y;

            float dx = (corners[2].Y * xx) / yy;

            int minx = (int)(corners[0].X - dx);
            int maxx = (int)(corners[2].X + dx);

            minx = (int)MathHelper.Clamp(minx / 32, 0, blocks.Length-1);
            maxx = (int)MathHelper.Clamp(maxx / 32, 0, blocks.Length-1);

            leftFrameBlock = minx;
            rightFrameBlock = maxx;
        }