public void CullScene(Common.IBoundingVolumeHierarchy<Entity> quadTree)
        {
            if ((DateTime.Now - lastEntityCull).TotalSeconds >= Renderer.Settings.CullSceneInterval || ForceCull)
            {
                ForceCull = false;
                lastEntityCull = DateTime.Now;
                if (firstEntityCull)
                {
                    firstEntityCull = false;
                    lastShadowEntityCull = DateTime.Now.Subtract(new TimeSpan(0, 0, 0, 0, (int)(Renderer.Settings.CullSceneInterval / 2f * 1000f)));
                }

                if (quadTree != null)
                    cachedEntities = quadTree.Cull(FrustumWithMargin(scene.Camera, scene.Viewport));
                else
                    cachedEntities = new List<Entity>(scene.AllEntities);
            }
            else if ((DateTime.Now - lastShadowEntityCull).TotalSeconds >= Renderer.Settings.CullSceneInterval || ForceShadowCull)
            {
                ForceShadowCull = false;
                lastShadowEntityCull = DateTime.Now;
                if (Renderer.Settings.ShadowQuality != Settings.ShadowQualities.NoShadows)
                {
                    if (quadTree != null)
                        cachedShadowEntities = quadTree.Cull(Camera.Frustum(Renderer.ShadowMapCamera));     // TODO: make frustum bigger?
                    else
                        cachedShadowEntities = new List<Entity>(scene.AllEntities);
                }
            }

            Renderer.Frame++;
            if (Renderer.Settings.ShadowQuality != Settings.ShadowQualities.NoShadows)
                foreach (Entity e in new List<Entity>(cachedShadowEntities))
                {
                    if (e.IsVisible && !e.IsRemoved)
                    {
                        e.ActiveInShadowMap = Renderer.Frame;
                        e.EnsureConstructed();
                    }
                }

            foreach (Entity e in new List<Entity>(cachedEntities))
            {
                if (e.IsVisible && !e.IsRemoved)
                {
                    e.ActiveInMain = Renderer.Frame;
                    if (Renderer.Settings.ShadowQuality == Settings.ShadowQualities.NoShadows)
                        e.EnsureConstructed();
                }
            }
            //if (i % 40 == 0)
            //{
                //if (i % 400 == 0)
                //    Console.Clear();
                //Console.WriteLine("ShadowEntities: " + cachedShadowEntities.Count);
                //Console.WriteLine("Entities: " + cachedEntities.Count);
            //}
            //i++;
        }