From 8fa22260d2c06b7a94c4a906bfefbaf3cfb03aec Mon Sep 17 00:00:00 2001
From: cosmonaut <evan@moonside.games>
Date: Mon, 19 Oct 2020 18:22:54 -0700
Subject: [PATCH] frustum culling

---
 Geometry/Mesh.cs     | 11 ++++++++++
 Geometry/MeshPart.cs |  4 ++++
 Geometry/Model.cs    |  9 ++++++++
 Renderer.cs          | 52 ++++++++++++++++++++++++++++++++++++++++----
 4 files changed, 72 insertions(+), 4 deletions(-)

diff --git a/Geometry/Mesh.cs b/Geometry/Mesh.cs
index 3d23b44..32c7afc 100644
--- a/Geometry/Mesh.cs
+++ b/Geometry/Mesh.cs
@@ -1,12 +1,23 @@
+using Microsoft.Xna.Framework;
+
 namespace Kav
 {
     public class Mesh
     {
         public MeshPart[] MeshParts { get; }
+        public BoundingBox BoundingBox { get; }
 
         public Mesh(MeshPart[] meshParts)
         {
             MeshParts = meshParts;
+
+            BoundingBox boundingBox = new BoundingBox();
+            foreach (var meshPart in MeshParts)
+            {
+                boundingBox = BoundingBox.CreateMerged(boundingBox, meshPart.BoundingBox);
+            }
+
+            BoundingBox = boundingBox;
         }
     }
 }
diff --git a/Geometry/MeshPart.cs b/Geometry/MeshPart.cs
index 248fb1a..25cb93c 100644
--- a/Geometry/MeshPart.cs
+++ b/Geometry/MeshPart.cs
@@ -9,6 +9,8 @@ namespace Kav
         public VertexBuffer VertexBuffer { get; }
         public Triangle[] Triangles { get; }
         public Vector3[] Positions { get; }
+
+        public BoundingBox BoundingBox { get; }
         
         private Texture2D albedoTexture = null;
         private Texture2D normalTexture = null;
@@ -50,6 +52,8 @@ namespace Kav
             IndexBuffer = indexBuffer;
             Positions = positions;
             Triangles = triangles;
+
+            BoundingBox = BoundingBox.CreateFromPoints(Positions);
         }
     }
 }
diff --git a/Geometry/Model.cs b/Geometry/Model.cs
index 9ab1dc0..6ffe912 100644
--- a/Geometry/Model.cs
+++ b/Geometry/Model.cs
@@ -5,6 +5,7 @@ namespace Kav
     public class Model
     {
         public Mesh[] Meshes { get; }
+        public BoundingBox BoundingBox { get; }
 
         public Color Albedo 
         { 
@@ -51,6 +52,14 @@ namespace Kav
         public Model(Mesh[] meshes)
         {
             Meshes = meshes;
+
+            BoundingBox boundingBox = new BoundingBox();
+            foreach (var mesh in Meshes)
+            {
+                boundingBox = BoundingBox.CreateMerged(boundingBox, mesh.BoundingBox);
+            }
+
+            BoundingBox = boundingBox;
         }
 
         public void DisableAlbedoMaps()
diff --git a/Renderer.cs b/Renderer.cs
index 3eb2440..2ad0ceb 100644
--- a/Renderer.cs
+++ b/Renderer.cs
@@ -240,7 +240,9 @@ namespace Kav
             PerspectiveCamera camera,
             IEnumerable<(Model, Matrix)> modelTransforms
         ) {
-            foreach (var (model, transform) in modelTransforms)
+            var boundingFrustum = new BoundingFrustum(camera.View * camera.Projection);
+
+            foreach (var (model, transform) in FrustumCull(boundingFrustum, modelTransforms))
             {
                 foreach (var modelMesh in model.Meshes)
                 {
@@ -312,7 +314,9 @@ namespace Kav
             GraphicsDevice.DepthStencilState = DepthStencilState.Default;
             GraphicsDevice.BlendState = BlendState.Opaque;
 
-            foreach (var (model, transform) in modelTransforms)
+            var boundingFrustum = new BoundingFrustum(camera.View * camera.Projection);
+
+            foreach (var (model, transform) in FrustumCull(boundingFrustum, modelTransforms))
             {
                 foreach (var modelMesh in model.Meshes)
                 {
@@ -581,7 +585,9 @@ namespace Kav
                 effect.LightSpaceMatrixFour = lightSpaceMatrix;
             }
 
-            foreach (var (model, transform) in modelTransforms)
+            var boundingFrustum = new BoundingFrustum(lightSpaceMatrix);
+            
+            foreach (var (model, transform) in FrustumCull(boundingFrustum, modelTransforms))
             {
                 foreach (var modelMesh in model.Meshes)
                 {
@@ -677,7 +683,9 @@ namespace Kav
                     targetUpDirection
                 );
 
-                foreach (var (model, transform) in modelTransforms)
+                var boundingFrustum = new BoundingFrustum(LinearDepthEffect.View * LinearDepthEffect.Projection);
+
+                foreach (var (model, transform) in FrustumCull(boundingFrustum, modelTransforms))
                 {
                     foreach (var modelMesh in model.Meshes)
                     {
@@ -706,5 +714,41 @@ namespace Kav
                 }
             }
         }
+
+        private static IEnumerable<(Model, Matrix)> FrustumCull(
+            BoundingFrustum boundingFrustum,
+            IEnumerable<(Model, Matrix)> modelTransforms
+        ) {
+            foreach (var modelTransform in modelTransforms)
+            {
+                var boundingBox = TransformedBoundingBox(modelTransform.Item1.BoundingBox, modelTransform.Item2);
+                var containment = boundingFrustum.Contains(boundingBox);
+                if (containment != ContainmentType.Disjoint)
+                {
+                    yield return modelTransform;
+                }
+            }
+        }
+
+        private static BoundingBox TransformedBoundingBox(BoundingBox boundingBox, Matrix matrix)
+        {
+            var center = (boundingBox.Min + boundingBox.Max) / 2f;
+            var extent = (boundingBox.Max - boundingBox.Min) / 2f;
+
+            var newCenter = Vector3.Transform(center, matrix);
+            var newExtent = Vector3.TransformNormal(extent, AbsoluteMatrix(matrix));
+
+            return new BoundingBox(newCenter - newExtent, newCenter + newExtent);
+        }
+
+        private static Matrix AbsoluteMatrix(Matrix matrix)
+        {
+            return new Matrix(
+                Math.Abs(matrix.M11), Math.Abs(matrix.M12), Math.Abs(matrix.M13), Math.Abs(matrix.M14),
+                Math.Abs(matrix.M21), Math.Abs(matrix.M22), Math.Abs(matrix.M23), Math.Abs(matrix.M24),
+                Math.Abs(matrix.M31), Math.Abs(matrix.M32), Math.Abs(matrix.M33), Math.Abs(matrix.M34),
+                Math.Abs(matrix.M41), Math.Abs(matrix.M42), Math.Abs(matrix.M43), Math.Abs(matrix.M44)
+            );
+        }
     }
 }