implement different kinds of billboarding

Cameras/Camera.cs

@@ -16,8 +16,15 @@ namespace Kav
         public float NearPlane { get; }
         public float FarPlane { get; }
 
-        public PerspectiveCamera(Vector3 position, Vector3 forward, Vector3 up, float fieldOfView, float aspectRatio, float nearPlane, float farPlane)
-        {
+        public PerspectiveCamera(
+            Vector3 position,
+            Vector3 forward,
+            Vector3 up,
+            float fieldOfView,
+            float aspectRatio,
+            float nearPlane,
+            float farPlane
+        ) {
             Position = position;
             Forward = forward;
             Up = up;

Enums/SpriteBillboardConstraint.cs

@@ -0,0 +1,9 @@
+namespace Kav
+{
+    public enum SpriteBillboardConstraint
+    {
+        None,
+        Horizontal,
+        Full
+    }
+}

Geometry/Sprite.cs

@@ -10,30 +10,48 @@ namespace Kav
         public Vector2 Origin { get; }
         public float Rotation { get; }
         public Vector2 Scale { get; }
+        public SpriteBillboardConstraint BillboardConstraint { get; }
+
+        public Matrix TransformMatrix { get; }
 
         public Sprite(
             Texture2D texture,
             Vector3 position,
             Vector2 origin,
             float rotation,
-            Vector2 scale
+            Vector2 scale,
+            SpriteBillboardConstraint billboardConstraint = SpriteBillboardConstraint.None
         ) {
             Texture = texture;
             Position = position;
             Origin = origin;
             Rotation = rotation;
             Scale = scale;
+            BillboardConstraint = billboardConstraint;
+            TransformMatrix = ConstructTransformMatrix(Position, Scale);
         }
 
         public Sprite(
             Texture2D texture,
-            Vector3 position
+            Vector3 position,
+            SpriteBillboardConstraint billboardConstraint = SpriteBillboardConstraint.None
         ) {
             Texture = texture;
             Position = position;
             Origin = Vector2.Zero;
-            Rotation = 0f;
+            Rotation = 0;
             Scale = Vector2.One;
+            BillboardConstraint = billboardConstraint;
+            TransformMatrix = ConstructTransformMatrix(Position, Scale);
+        }
+
+        private static Matrix ConstructTransformMatrix(
+            Vector3 position,
+            Vector2 scale
+        ) {
+            return
+                Matrix.CreateTranslation(position) *
+                Matrix.CreateScale(scale.X, scale.Y, 1);
         }
     }
 }

Renderer.cs

@@ -254,35 +254,53 @@ namespace Kav
             DepthRender(camera, modelTransforms);
             GraphicsDevice.Clear(ClearOptions.Target, new Color(0, 0, 0, 0), 1f, 0);
 
-            Matrix invertY = Matrix.CreateScale(1, -1, 1);
-
-            BasicEffect.World = invertY;
-            BasicEffect.View = Matrix.Identity;
+            BasicEffect.View = camera.View;
             BasicEffect.Projection = camera.Projection;
             BasicEffect.TextureEnabled = true;
             BasicEffect.VertexColorEnabled = true;
 
-            SpriteBatch.Begin(0, null, null, DepthStencilState.DepthRead, RasterizerState.CullNone, BasicEffect);
-
             foreach (var sprite in sprites)
             {
-                // transform view space on CPU so we don't have to break the batch
-                Vector3 viewSpacePosition = Vector3.Transform(sprite.Position, camera.View * invertY);
+                if (sprite.BillboardConstraint == SpriteBillboardConstraint.None)
+                {
+                    BasicEffect.World = sprite.TransformMatrix;
+                }
+                else if (sprite.BillboardConstraint == SpriteBillboardConstraint.Horizontal)
+                {
+                    BasicEffect.World = Matrix.CreateConstrainedBillboard(
+                        sprite.Position,
+                        camera.Position,
+                        Vector3.Up,
+                        camera.Forward,
+                        camera.Position - sprite.Position
+                    );
+                }
+                else
+                {
+                    BasicEffect.World = Matrix.CreateConstrainedBillboard(
+                        sprite.Position,
+                        camera.Position,
+                        Vector3.Up,
+                        null,
+                        null
+                    );
+                }
 
+                SpriteBatch.Begin(0, null, null, DepthStencilState.DepthRead, RasterizerState.CullNone, BasicEffect);
                 SpriteBatch.Draw(
                     sprite.Texture,
-                    new Vector2(viewSpacePosition.X, viewSpacePosition.Y),
+                    Vector2.Zero,
                     null,
                     Color.White,
-                    0,
+                    sprite.Rotation,
                     sprite.Origin,
-                    sprite.Scale / new Vector2(sprite.Texture.Width, sprite.Texture.Height),
+                    sprite.Scale / new Vector2(sprite.Texture.Width, -sprite.Texture.Height),
                     0,
-                    viewSpacePosition.Z
+                    0
                 );
+                SpriteBatch.End();
             }
 
-            SpriteBatch.End();
 
             GraphicsDevice.SetRenderTarget(renderTarget);
             GraphicsDevice.Clear(new Color(0, 0, 0, 0));