Add ColliderComponent and add it to entities that can be collided with.

Only entities with ColliderComponent will be checked for collisions.

Also, don't check collisions with inactive/removed entities.

core/src/com/me/asteroids/EntityFactory.java

@@ -6,6 +6,7 @@ import com.badlogic.gdx.math.Vector2;
 import com.me.asteroids.components.AccelerationComponent;
 import com.me.asteroids.components.AsteroidComponent;
 import com.me.asteroids.components.BulletComponent;
+import com.me.asteroids.components.ColliderComponent;
 import com.me.asteroids.components.DebrisComponent;
 import com.me.asteroids.components.ModelComponent;
 import com.me.asteroids.components.PlayerComponent;
@@ -28,6 +29,8 @@ public class EntityFactory {
     private static final Vector2 tmpA = new Vector2();
     private static final Vector2 tmpB = new Vector2();
 
+    private static final ColliderComponent COLLIDER = new ColliderComponent();
+
     private static Entity createEntity(Engine engine) {
         Entity entity = engine.createEntity();
         if (Constants.DEBUG) {
@@ -64,6 +67,7 @@ public class EntityFactory {
         player.addComponent(velocity);
         player.addComponent(model);
         player.addComponent(accel);
+        player.addComponent(COLLIDER);
         player.addComponent(new PlayerComponent());
         return player;
     }
@@ -161,6 +165,7 @@ public class EntityFactory {
         bullet.addComponent(position);
         bullet.addComponent(velocity);
         bullet.addComponent(model);
+        bullet.addComponent(COLLIDER);
         bullet.addComponent(new BulletComponent());
         return bullet;
     }
@@ -185,6 +190,7 @@ public class EntityFactory {
         asteroid.addComponent(position);
         asteroid.addComponent(velocity);
         asteroid.addComponent(model);
+        asteroid.addComponent(COLLIDER);
         asteroid.addComponent(new AsteroidComponent());
         return asteroid;
     }
@@ -236,6 +242,7 @@ public class EntityFactory {
             split.addComponent(position);
             split.addComponent(velocity);
             split.addComponent(asteroidComponent);
+            split.addComponent(COLLIDER);
             entities[i] = split;
         }
 

core/src/com/me/asteroids/components/ColliderComponent.java

@@ -0,0 +1,9 @@
+package com.me.asteroids.components;
+
+import com.me.common.ecs.Component;
+
+/**
+ * Add this to Entities that should be checked for collisions with other entities.
+ */
+public class ColliderComponent implements Component {
+}

core/src/com/me/asteroids/screens/GameScreen.java

@@ -11,6 +11,7 @@ import com.me.asteroids.Graphics;
 import com.me.asteroids.components.AccelerationComponent;
 import com.me.asteroids.components.AsteroidComponent;
 import com.me.asteroids.components.BulletComponent;
+import com.me.asteroids.components.ColliderComponent;
 import com.me.asteroids.components.DebrisComponent;
 import com.me.asteroids.components.ModelComponent;
 import com.me.asteroids.components.PlayerComponent;
@@ -58,6 +59,7 @@ public class GameScreen extends Screen implements Listener {
         engine.registerComponentClass(BulletComponent.class);
         engine.registerComponentClass(AsteroidComponent.class);
         engine.registerComponentClass(DebrisComponent.class);
+        engine.registerComponentClass(ColliderComponent.class);
         engine.registerComponentClass(PositionComponent.class);
         engine.registerComponentClass(VelocityComponent.class);
         engine.registerComponentClass(AccelerationComponent.class);

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

@@ -2,6 +2,7 @@ package com.me.asteroids.systems;
 
 import com.badlogic.gdx.math.Rectangle;
 import com.me.asteroids.EventFactory;
+import com.me.asteroids.components.ColliderComponent;
 import com.me.asteroids.components.ModelComponent;
 import com.me.common.ecs.ComponentMapper;
 import com.me.common.ecs.Engine;
@@ -13,7 +14,7 @@ public class CollisionSystem extends EntitySystem {
     private ComponentMapper<ModelComponent> modelMapper;
 
     public CollisionSystem(Engine engine) {
-        super(engine, ModelComponent.class);
+        super(engine, ColliderComponent.class, ModelComponent.class);
         modelMapper = engine.getComponentMapper(ModelComponent.class);
     }
 
@@ -22,10 +23,17 @@ public class CollisionSystem extends EntitySystem {
         Entity[] entities = getEntities().items;
         for (int i = 0, n = getEntities().size; i < n-1; i++) {
             Entity entityA = entities[i];
+            if (!entityA.isActive() || entityA.isRemoved()) {
+                continue;
+            }
+
             Rectangle aabbA = modelMapper.get(entityA).model.getBoundingBox();
 
             for (int j = i + 1; j < n; j++) {
                 Entity entityB = entities[j];
+                if (!entityB.isActive() || entityB.isRemoved()) {
+                    continue;
+                }
 
                 Rectangle aabbB = modelMapper.get(entityB).model.getBoundingBox();
                 if (aabbA.overlaps(aabbB)) {