encompass-cs/Exceptions/IllegalDrawLayerException.cs

@@ -0,0 +1,13 @@
+
+using System;
+
+namespace Encompass.Exceptions
+{
+    public class IllegalDrawLayerException : Exception
+    {
+        public IllegalDrawLayerException(
+            string format,
+            params object[] args
+        ) : base(string.Format(format, args)) { }
+    }
+}

encompass-cs/WorldBuilder.cs

@@ -33,15 +33,13 @@ namespace Encompass
         private readonly TrackingManager _trackingManager;
 
         private readonly Dictionary<Type, HashSet<Engine>> _typeToReaders = new Dictionary<Type, HashSet<Engine>>();
-
         private readonly HashSet<Engine> _senders = new HashSet<Engine>();
-
         private readonly HashSet<Type> _componentTypesToPreload = new HashSet<Type>();
-
         private readonly HashSet<Type> _messageTypes = new HashSet<Type>();
-
         private readonly Dictionary<Type, int> _typeToIndex = new Dictionary<Type, int>();
 
+        private bool _rendererRegistered = false;
+
         public WorldBuilder(int entityCapacity = 32768)
         {
             _entityCapacity = entityCapacity;
@@ -177,6 +175,10 @@ namespace Encompass
         /// <param name="layer">The draw layer to register.</param>
         public void RegisterDrawLayer(int layer)
         {
+            if (_rendererRegistered) 
+            { 
+                throw new IllegalDrawLayerException("Cannot register a draw layer after a Renderer has been registered.");
+            }
             _drawLayerManager.RegisterDrawLayer(layer);
         }
 
@@ -189,6 +191,7 @@ namespace Encompass
             renderer.AssignEntityManager(_entityManager);
             renderer.AssignComponentManager(_componentManager);
             _renderManager.RegisterOrderedRenderer<TComponent>(renderer.InternalRender);
+            _rendererRegistered = true;
             return renderer;
         }
 
@@ -202,9 +205,8 @@ namespace Encompass
         {
             renderer.AssignEntityManager(_entityManager);
             renderer.AssignComponentManager(_componentManager);
-
             _renderManager.RegisterGeneralRendererWithLayer(renderer, layer);
-
+            _rendererRegistered = true;
             return renderer;
         }
 

test/WorldBuilderTest.cs

@@ -558,5 +558,38 @@ namespace Tests
                 Assert.That(order.IndexOf(engineA), Is.LessThan(order.IndexOf(engineB)));
             }
         }
+
+        public class DrawLayerRegister
+        {
+            struct AComponent : IComponent, IDrawableComponent
+            {
+                public int Layer { get; set; }
+            }
+
+            class ARenderer : OrderedRenderer<AComponent>
+            {
+
+                public override void Render(Entity entity, in AComponent drawComponent) { }
+            }
+
+            [Test]
+            public void DrawLayerRegisterAfterOrderedRendererRegisterThrows()
+            {
+                var worldBuilder = new WorldBuilder();
+
+                var rendererA = worldBuilder.AddOrderedRenderer(new ARenderer());
+
+                Assert.Throws<IllegalDrawLayerException>(() => worldBuilder.RegisterDrawLayer(1));
+            }
+
+            [Test]
+            public void DrawLayerRegisterBeforeOrderedRendererDoesNotThrow()
+            {
+                var worldBuilder = new WorldBuilder();
+
+                Assert.DoesNotThrow(() => worldBuilder.RegisterDrawLayer(1));
+                Assert.DoesNotThrow(() => worldBuilder.AddOrderedRenderer(new ARenderer()));
+            }
+        }
     }
 }