adds EntityExists method + fixes crash when destroying an entity that has no components

encompass-cs/ComponentManager.cs

@@ -37,6 +37,11 @@ namespace Encompass
             this.entitiesWithRemovedComponents = entitiesWithRemovedComponents;
         }
 
+        internal void RegisterEntity(Guid entityID)
+        {
+            entityIDToComponentIDs.Add(entityID, new List<Guid>());
+        }
+
         internal Guid AddComponent<TComponent>(Guid entityID, TComponent component) where TComponent : struct, IComponent
         {
             var componentID = Guid.NewGuid();
@@ -51,11 +56,6 @@ namespace Encompass
 
             typeToComponentIDs[typeof(TComponent)].Add(componentID);
 
-            if (!entityIDToComponentIDs.ContainsKey(entityID))
-            {
-                entityIDToComponentIDs.Add(entityID, new List<Guid>());
-            }
-
             entityIDToComponentIDs[entityID].Add(componentID);
             componentIDToEntityID[componentID] = entityID;
 

encompass-cs/Engine.cs

@@ -59,6 +59,11 @@ namespace Encompass
             return entityManager.CreateEntity();
         }
 
+        protected bool EntityExists(Guid entityID)
+        {
+            return entityManager.EntityExists(entityID);
+        }
+
         protected Entity GetEntity(Guid entityID)
         {
             return entityManager.GetEntity(entityID);

encompass-cs/EntityManager.cs

@@ -33,9 +33,15 @@ namespace Encompass
             var id = NextID();
             var entity = new Entity(id, componentManager);
             IDToEntity[id] = entity;
+            componentManager.RegisterEntity(id);
             return entity;
         }
 
+        public bool EntityExists(Guid id)
+        {
+            return IDToEntity.ContainsKey(id);
+        }
+
         public Entity GetEntity(Guid id)
         {
             return IDToEntity[id];

encompass-cs/RenderManager.cs

@@ -54,7 +54,7 @@ namespace Encompass
                         var renderer = drawComponentTypeToEntityRenderer[componentType];
                         var entityID = componentManager.GetEntityIDByComponentID(componentID);
 
-                        if (renderer.IsTracking(entityID))
+                        if (renderer.IsTracking(entityID) && entityManager.EntityExists(entityID))
                         {
                             var entity = entityManager.GetEntity(entityID);
                             renderer.Render(entity);

encompass-cs/Renderer.cs

@@ -19,6 +19,11 @@ namespace Encompass
             this.componentManager = componentManager;
         }
 
+        protected bool EntityExists(Guid entityID)
+        {
+            return entityManager.EntityExists(entityID);
+        }
+
         protected Entity GetEntity(Guid entityID)
         {
             return entityManager.GetEntity(entityID);

test/EngineTest.cs

@@ -556,5 +556,44 @@ namespace Tests
 
             Assert.Throws<ComponentTypeMismatchException>(() => world.Update(0.01f));
         }
+
+        struct EntityIDComponent : IComponent { public Guid entityID;  }
+        static bool hasEntity;
+        class HasEntityTestEngine : Engine
+        {
+            public override void Update(double dt)
+            {
+                foreach (var (mockComponentID, mockComponent) in ReadComponents<EntityIDComponent>())
+                {
+                    hasEntity = EntityExists(mockComponent.entityID);
+                    if (hasEntity) { Destroy(mockComponent.entityID); }
+                }
+            }
+        }
+
+        [Test]
+        public void EntityExists()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine(new HasEntityTestEngine());
+
+            var entity = worldBuilder.CreateEntity();
+            var entityTwo = worldBuilder.CreateEntity();
+
+            EntityIDComponent entityIDComponent;
+            entityIDComponent.entityID = entityTwo.id;
+
+            entity.AddComponent(entityIDComponent);
+
+            var world = worldBuilder.Build();
+
+            world.Update(0.01);
+
+            Assert.IsTrue(hasEntity);
+
+            world.Update(0.01);
+
+            Assert.IsFalse(hasEntity);
+        }
     }
 }