decouple billboard constraints from meshsprite

Geometry/MeshSprite.cs

@@ -19,7 +19,6 @@ namespace Kav
 
         public Texture2D Texture { get; }
         public Texture2D Normal { get; }
-        public SpriteBillboardConstraint BillboardConstraint { get; }
 
         public IndexBuffer IndexBuffer { get; }
         public VertexBuffer VertexBuffer { get; }
@@ -27,12 +26,10 @@ namespace Kav
 
         public MeshSprite(
             GraphicsDevice graphicsDevice,
-            Texture2D texture,
+            Texture2D texture
-            SpriteBillboardConstraint billboardConstraint
         ) {
             Texture = texture;
             Normal = null;
-            BillboardConstraint = billboardConstraint;
 
 			IndexBuffer = new IndexBuffer(
 				graphicsDevice,
@@ -58,12 +55,10 @@ namespace Kav
         public MeshSprite(
             GraphicsDevice graphicsDevice,
             Texture2D texture,
-            Texture2D normal,
+            Texture2D normal
-            SpriteBillboardConstraint billboardConstraint
         ) {
             Texture = texture;
             Normal = normal;
-            BillboardConstraint = billboardConstraint;
 
 			IndexBuffer = new IndexBuffer(
 				graphicsDevice,

Renderer.cs

@@ -104,7 +104,7 @@ namespace Kav
         public void MeshSpriteRender(
             RenderTarget2D renderTarget,
             PerspectiveCamera camera,
-            IEnumerable<(MeshSprite, Matrix)> meshSpriteTransforms,
+            IEnumerable<(MeshSprite, SpriteBillboardConstraint, Matrix)> meshSpriteBillboardTransforms,
             AmbientLight ambientLight,
             IEnumerable<PointLight> pointLights,
             DirectionalLight? directionalLight
@@ -145,34 +145,11 @@ namespace Kav
 
             var boundingFrustum = new BoundingFrustum(camera.View * camera.Projection);
 
-            foreach (var (sprite, transform) in FrustumCull(boundingFrustum, meshSpriteTransforms))
+            foreach (var (sprite, transform) in FrustumCull(boundingFrustum, BillboardTransforms(camera, meshSpriteBillboardTransforms)))
             {
                 DiffuseLitSpriteEffect.NormalMapEnabled = sprite.Normal != null;
 
-                if (sprite.BillboardConstraint == SpriteBillboardConstraint.None)
-                {
                 DiffuseLitSpriteEffect.World = transform;
-                }
-                else if (sprite.BillboardConstraint == SpriteBillboardConstraint.Horizontal)
-                {
-                    DiffuseLitSpriteEffect.World = Matrix.CreateConstrainedBillboard(
-                        transform.Translation,
-                        camera.Position,
-                        Vector3.Up,
-                        camera.Forward,
-                        camera.Position - transform.Translation
-                    );
-                }
-                else
-                {
-                    DiffuseLitSpriteEffect.World = Matrix.CreateConstrainedBillboard(
-                        transform.Translation,
-                        camera.Position,
-                        Vector3.Up,
-                        null,
-                        null
-                    );
-                }
 
                 GraphicsDevice.Textures[0] = sprite.Texture;
                 GraphicsDevice.Textures[1] = sprite.Normal;
@@ -196,6 +173,39 @@ namespace Kav
             }
         }
 
+        private IEnumerable<(MeshSprite, Matrix)> BillboardTransforms(
+            PerspectiveCamera camera,
+            IEnumerable<(MeshSprite, SpriteBillboardConstraint, Matrix)> meshSpriteBillboardTransforms
+        ) {
+            foreach (var (sprite, billboardConstraint, transform) in meshSpriteBillboardTransforms)
+            {
+                if (billboardConstraint == SpriteBillboardConstraint.None)
+                {
+                    yield return (sprite, transform);
+                }
+                else if (billboardConstraint == SpriteBillboardConstraint.Horizontal)
+                {
+                    yield return (sprite, Matrix.CreateConstrainedBillboard(
+                        transform.Translation,
+                        camera.Position,
+                        Vector3.Up,
+                        camera.Forward,
+                        camera.Position - transform.Translation
+                    ));
+                }
+                else
+                {
+                    yield return (sprite, Matrix.CreateConstrainedBillboard(
+                        transform.Translation,
+                        camera.Position,
+                        Vector3.Up,
+                        null,
+                        null
+                    ));
+                }
+            }
+        }
+
         // Renders a series of drawable-transform pairs using an effect that has a World matrix.
         // Effect must be pre-configured!!
         public static void CullAndRenderIndexed<T, U>(
@@ -243,7 +253,6 @@ namespace Kav
 
         public static int FillAndSetBuffersForInstancing<T, V>(
             GraphicsDevice graphicsDevice,
-            BoundingFrustum boundingFrustum,
             T drawable,
             IEnumerable<Matrix> transforms,
             V[] vertexData,
@@ -251,7 +260,7 @@ namespace Kav
         ) where T : ICullable, IIndexDrawable where V : struct, IVertexType, IHasTranslation
         {
             int numInstances = 0;
-            foreach (var transform in FrustumCull(boundingFrustum, drawable, transforms))
+            foreach (var transform in transforms)
             {
                 vertexData[numInstances].Translation = transform.Translation;
                 numInstances += 1;
@@ -385,13 +394,14 @@ namespace Kav
 
             var numInstances = FillAndSetBuffersForInstancing(
                 GraphicsDevice,
-                new BoundingFrustum(camera.View * camera.Projection),
                 drawable,
                 transforms,
                 PositionInstanceVertices,
                 PositionInstanceVertexBuffer
             );
 
+            if (numInstances == 0) { return; }
+
             RenderInstanced(
                 GraphicsDevice,
                 drawable, 
@@ -738,7 +748,6 @@ namespace Kav
 
             var numInstances = FillAndSetBuffersForInstancing(
                 GraphicsDevice, 
-                new BoundingFrustum(SimpleDepthEffectInstanced.View * SimpleDepthEffectInstanced.Projection),
                 drawable,
                 transforms,
                 PositionInstanceVertices,