From fc09082f1b049b05799aa36ac768f622ec78d20d Mon Sep 17 00:00:00 2001
From: cosmonaut <evan@moonside.games>
Date: Sun, 6 Dec 2020 19:27:46 -0800
Subject: [PATCH] frustum cull meshsprites

---
 Geometry/MeshSprite.cs | 28 +++++++++++++++++++++++-----
 Renderer.cs            | 19 ++++++++++++++++++-
 2 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/Geometry/MeshSprite.cs b/Geometry/MeshSprite.cs
index 87dac1c..a7cca6c 100644
--- a/Geometry/MeshSprite.cs
+++ b/Geometry/MeshSprite.cs
@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using Microsoft.Xna.Framework;
 using Microsoft.Xna.Framework.Graphics;
 
@@ -16,13 +17,14 @@ namespace Kav
             2
         };
 
-        public IndexBuffer IndexBuffer { get; }
-        public VertexBuffer VertexBuffer { get; }
-
         public Texture2D Texture { get; }
         public Texture2D Normal { get; }
         public SpriteBillboardConstraint BillboardConstraint { get; }
 
+        public IndexBuffer IndexBuffer { get; }
+        public VertexBuffer VertexBuffer { get; }
+        public BoundingBox BoundingBox { get; }
+
         public MeshSprite(
             GraphicsDevice graphicsDevice,
             Texture2D texture,
@@ -40,13 +42,17 @@ namespace Kav
 			);
             IndexBuffer.SetData(Indices);
 
+            var vertexArray = GenerateVertexArray(Texture);
+
             VertexBuffer = new VertexBuffer(
                 graphicsDevice,
                 typeof(VertexPositionNormalTexture),
                 4,
                 BufferUsage.WriteOnly
             );
-            VertexBuffer.SetData(GenerateVertexArray(Texture));
+            VertexBuffer.SetData(vertexArray);
+
+            BoundingBox = BoundingBox.CreateFromPoints(Positions(vertexArray));
         }
 
         public MeshSprite(
@@ -67,13 +73,17 @@ namespace Kav
 			);
             IndexBuffer.SetData(Indices);
 
+            var vertexArray = GenerateVertexArray(Texture);
+
             VertexBuffer = new VertexBuffer(
                 graphicsDevice,
                 typeof(VertexPositionNormalTexture),
                 4,
                 BufferUsage.WriteOnly
             );
-            VertexBuffer.SetData(GenerateVertexArray(Texture));
+            VertexBuffer.SetData(vertexArray);
+
+            BoundingBox = BoundingBox.CreateFromPoints(Positions(vertexArray));
         }
 
         private static VertexPositionNormalTexture[] GenerateVertexArray(Texture2D texture)
@@ -98,5 +108,13 @@ namespace Kav
 
             return result;
         }
+
+        private static IEnumerable<Vector3> Positions(IEnumerable<VertexPositionNormalTexture> vertices)
+        {
+            foreach (var vertex in vertices)
+            {
+                yield return vertex.Position;
+            }
+        }
     }
 }
diff --git a/Renderer.cs b/Renderer.cs
index 28d510c..b45ac9a 100644
--- a/Renderer.cs
+++ b/Renderer.cs
@@ -297,7 +297,9 @@ namespace Kav
                 i += 1;
             }
 
-            foreach (var (sprite, transform) in meshSpriteTransforms)
+            var boundingFrustum = new BoundingFrustum(camera.View * camera.Projection);
+
+            foreach (var (sprite, transform) in FrustumCull(boundingFrustum, meshSpriteTransforms))
             {
                 DiffuseLitSpriteEffect.NormalMapEnabled = sprite.Normal != null;
 
@@ -849,6 +851,21 @@ namespace Kav
             }
         }
 
+        private static IEnumerable<(MeshSprite, Matrix)> FrustumCull(
+            BoundingFrustum boundingFrustum,
+            IEnumerable<(MeshSprite, Matrix)> meshSpriteTransforms
+        ) {
+            foreach (var (meshSprite, transform) in meshSpriteTransforms)
+            {
+                var boundingBox = TransformedBoundingBox(meshSprite.BoundingBox, transform);
+                var containment = boundingFrustum.Contains(boundingBox);
+                if (containment != ContainmentType.Disjoint)
+                {
+                    yield return (meshSprite, transform);
+                }
+            }
+        }
+
         private static BoundingBox TransformedBoundingBox(BoundingBox boundingBox, Matrix matrix)
         {
             var center = (boundingBox.Min + boundingBox.Max) / 2f;