feat: Listed trait

packages/entity/list.js

@@ -57,6 +57,11 @@ class EntityListBase {
     const uuid = entity.instanceUuid;
     this.entities_PRIVATE[uuid] = entity;
     this.state_PRIVATE = this.state_PRIVATE.set(uuid, entity.state());
+    entity.addTrait('listed', {
+      params: {
+        list: this,
+      },
+    });
     entity.on('destroyed', () => {
       this.removeEntity(entity);
     });
@@ -97,6 +102,8 @@ class EntityListBase {
     delete this.entities_PRIVATE[uuid];
     this.state_PRIVATE = this.state_PRIVATE.delete(uuid);
     this.emit('entityRemoved', entity);
+    entity.removeTrait('listed');
+    this.quadTree_PRIVATE.remove(this.quadTreePoint(entity));
   }
 
   state() {

packages/entity/traits/listed.js

@@ -0,0 +1,32 @@
+import * as I from 'immutable';
+
+import {Trait} from '@avocado/entity';
+import {Rectangle, Vector} from '@avocado/math';
+
+export class Listed extends Trait {
+
+  initialize() {
+    this._list = this.params.get('list');
+    this.params = this.params.delete('list');
+    this.lastNearby = I.Set();
+  }
+
+  get list() {
+    return this._list;
+  }
+
+  methods() {
+    return {
+
+      nearbyEntities: (size) => {
+        const position = Vector.add(
+          this.entity.position,
+          Vector.scale(size, -0.5)
+        );
+        return this._list.within(Rectangle.compose(position, size));
+      },
+
+    };
+  }
+
+}