Add BaseSystem which all systems (entity processing or not) extend from

core/src/com/me/asteroids/systems/CollisionSystem.java

@@ -18,7 +18,7 @@ public class CollisionSystem extends EntitySystem {
     }
 
     @Override
-    public void processEntities(float dt) {
+    public void process(float dt) {
         Entity[] entities = getEntities().items;
         for (int i = 0, n = getEntities().size; i < n-1; i++) {
             Entity entityA = entities[i];

core/src/com/me/asteroids/systems/ModelRenderSystem.java

@@ -23,7 +23,7 @@ public class ModelRenderSystem extends EntitySystem {
     }
 
     @Override
-    public void preProcessing() {
+    public void preProcess() {
         renderer.setColor(Color.WHITE);
         renderer.begin(ShapeRenderer.ShapeType.Line);
     }
@@ -37,7 +37,7 @@ public class ModelRenderSystem extends EntitySystem {
     }
 
     @Override
-    public void postProcessing() {
+    public void postProcess() {
         renderer.end();
     }
 

core/src/com/me/common/ecs/BaseSystem.java

@@ -0,0 +1,17 @@
+package com.me.common.ecs;
+
+public abstract class BaseSystem {
+
+    protected Engine engine;
+
+    public BaseSystem(Engine engine) {
+        this.engine = engine;
+    }
+
+    public void preProcess() {}
+
+    public abstract void process(float dt);
+
+    public void postProcess() {}
+
+}

core/src/com/me/common/ecs/Engine.java

@@ -15,7 +15,7 @@ public class Engine {
     private Array<Entity> toRemove;
 
     private ComponentBag[] components;
-    private Array<EntitySystem> systems;
+    private Array<BaseSystem> systems;
 
     private ListenerRegistry listenerRegistry;
 
@@ -64,10 +64,10 @@ public class Engine {
         deactivatePending();
         removePending();
 
-        for (EntitySystem system : systems) {
+        for (BaseSystem system : systems) {
-            system.preProcessing();
+            system.preProcess();
-            system.processEntities(dt);
+            system.process(dt);
-            system.postProcessing();
+            system.postProcess();
         }
     }
 
@@ -82,6 +82,32 @@ public class Engine {
         toRemove.add(entity);
     }
 
+    private void removeEntityFromSystems(Entity entity) {
+        for (BaseSystem system : systems) {
+            if (!(system instanceof EntitySystem)) {
+                continue;
+            }
+
+            EntitySystem entitySystem = (EntitySystem) system;
+            if (entitySystem.interestedIn(entity)) {
+                entitySystem.removeEntity(entity);
+            }
+        }
+    }
+
+    private void addEntityToSystems(Entity entity) {
+        for (BaseSystem system : systems) {
+            if (!(system instanceof EntitySystem)) {
+                continue;
+            }
+
+            EntitySystem entitySystem = (EntitySystem) system;
+            if (entitySystem.interestedIn(entity)) {
+                entitySystem.addEntity(entity);
+            }
+        }
+    }
+
     private void removePending() {
         if (toRemove.isEmpty()) {
             return;
@@ -90,6 +116,7 @@ public class Engine {
         for (Entity entity : toRemove) {
             removeAllEntityComponents(entity.getId());
             entities.removeValue(entity, true);
+            removeEntityFromSystems(entity);
         }
 
         toRemove.clear();
@@ -105,11 +132,7 @@ public class Engine {
         }
 
         for (Entity entity : toActivate) {
-            for (EntitySystem system : systems) {
+            addEntityToSystems(entity);
-                if (system.interestedIn(entity)) {
-                    system.entities.add(entity);
-                }
-            }
         }
         toActivate.clear();
     }
@@ -124,11 +147,8 @@ public class Engine {
         }
 
         for (Entity entity : toDeactivate) {
-            for (EntitySystem system : systems) {
+            removeEntityFromSystems(entity);
-                system.entities.removeValue(entity, true);
-            }
         }
-
         toDeactivate.clear();
     }
 

core/src/com/me/common/ecs/EntitySystem.java

@@ -2,26 +2,23 @@ package com.me.common.ecs;
 
 import com.badlogic.gdx.utils.Array;
 
-public abstract class EntitySystem {
+public abstract class EntitySystem extends BaseSystem {
 
     private long typeBits;
 
-    protected Engine engine;
     protected Array<Entity> entities;
 
     public EntitySystem(Engine engine, Class<? extends Component>... components) {
-        this.engine = engine;
+        super(engine);
         this.typeBits = ComponentType.getMaskBits(components);
         this.entities = new Array<>(true, 16, Entity.class);
     }
 
-    public void preProcessing() {}
-
     public Array<Entity> getEntities() {
         return entities;
     }
 
-    public void processEntities(float dt) {
+    public void process(float dt) {
         for (int i = 0, n = getEntities().size; i < n; i++) {
             processEntity(entities.get(i), dt);
         }
@@ -29,10 +26,16 @@ public abstract class EntitySystem {
 
     public abstract void processEntity(Entity entity, float dt);
 
-    public void postProcessing() {}
-
     public boolean interestedIn(Entity entity) {
         return (entity.getComponentBits() & typeBits) == typeBits;
     }
 
+    protected void addEntity(Entity entity) {
+        entities.add(entity);
+    }
+
+    protected void removeEntity(Entity entity) {
+        entities.removeValue(entity, true);
+    }
+
 }