Added priority rendering/updating to BaseGame

lib/components/component.dart

@@ -42,6 +42,14 @@ abstract class Component {
   ///
   /// HUD objects ignore the [BaseGame.camera] when rendered (so their position coordinates are considered relative to the device screen).
   bool isHud() => false;
+
+  /// Render priority of this component. This allows you to control the order in which your components are rendered.
+  ///
+  /// Components are always updated and rendered in the order defined by this number.
+  /// The smaller the priority, the sooner your component will be updated/rendered.
+  /// It can be any integer (negative, zero, or positive).
+  /// If two components share the same priority, they will probably be drawn in the order they were added.
+  int priority() => 0;
 }
 
 /// A [Component] implementation that represents a component that has a specific, possibly mutatable position on the screen.

lib/game.dart

@@ -6,6 +6,9 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/widgets.dart';
 
+import 'package:ordered_set/ordered_set.dart';
+import 'package:ordered_set/comparing.dart';
+
 import 'components/component.dart';
 import 'position.dart';
 
@@ -151,7 +154,7 @@ class _GameRenderBox extends RenderBox with WidgetsBindingObserver {
 /// It is based on the Component system.
 abstract class BaseGame extends Game {
   /// The list of components to be updated and rendered by the base game.
-  List<Component> components = [];
+  OrderedSet<Component> components = new OrderedSet(Comparing.on((c) => c.priority()));
 
   /// Components added by the [addLater] method
   List<Component> _addLater = [];

pubspec.yaml

@@ -10,7 +10,8 @@ flutter:
 dependencies:
   flutter:
     sdk: flutter
-  audioplayers: 0.5.2
+  audioplayers: ^0.5.2
+  ordered_set: ^1.1.0
   path_provider: ^0.4.0
   box2d: ^0.4.0