feat: add birds (#327)

packages/trashy_road/lib/src/game/components/trashy_road_world/trashy_road_world.dart

@@ -56,6 +56,8 @@ class TrashyRoadWorld extends PositionComponent {
     final obstaclesLayer = tileMap.getObjectGroup(_TiledLayer.obstacles.name);
     await addAll(obstaclesLayer.objects.map(Obstacle.fromTiledObject));
 
+    await addAll(Bird.randomAmount());
+
     await add(_TiledFloor());
 
     size = Vector2(tileMap.width.toDouble(), tileMap.height.toDouble());

packages/trashy_road/lib/src/game/entities/bird/behaviors/behaviors.dart

@@ -0,0 +1,2 @@
+export 'bird_flying_behavior.dart';
+export 'bird_random_spawning_behavior.dart';

packages/trashy_road/lib/src/game/entities/bird/behaviors/bird_flying_behavior.dart

@@ -0,0 +1,33 @@
+import 'package:flame/components.dart';
+import 'package:flame_behaviors/flame_behaviors.dart';
+import 'package:trashy_road/src/game/game.dart';
+
+class BirdFlyingBehavior extends Behavior<Bird>
+    with HasGameReference<TrashyRoadGame> {
+  /// The speed multiplier for the bird.
+  static const birdSpeedMultiplier = 30;
+
+  @override
+  void update(double dt) {
+    super.update(dt);
+
+    final distanceCovered = birdSpeedMultiplier * dt * parent.speed;
+
+    final direction = parent.isFlyingRight ? 1 : -1;
+    parent.position.x += distanceCovered * direction;
+
+    final isWithinBound = game.bounds!.isPointInside(parent.position);
+
+    // has exited the screen
+    if (!isWithinBound) {
+      parent.position.setAll(0);
+      if (parent.isFlyingRight) {
+        parent.position.x = 0;
+      } else {
+        parent.position.x = game.bounds!.bottomRight.x;
+      }
+
+      parent.position.y = Bird.random.nextDouble() * game.bounds!.bottomRight.y;
+    }
+  }
+}

packages/trashy_road/lib/src/game/entities/bird/behaviors/bird_random_spawning_behavior.dart

@@ -0,0 +1,17 @@
+import 'package:flame/components.dart';
+import 'package:flame_behaviors/flame_behaviors.dart';
+import 'package:trashy_road/src/game/game.dart';
+
+class BirdRandomSpawningBehavior extends Behavior<Bird>
+    with HasGameReference<TrashyRoadGame> {
+  @override
+  void onLoad() {
+    if (!parent.isFlyingRight) {
+      parent.flipHorizontally();
+    }
+
+    final x = Bird.random.nextDouble() * game.bounds!.bottomRight.x;
+    final y = Bird.random.nextDouble() * game.bounds!.bottomRight.y;
+    parent.position = Vector2(x, y);
+  }
+}

packages/trashy_road/lib/src/game/entities/bird/bird.dart

@@ -0,0 +1,63 @@
+import 'dart:math';
+
+import 'package:flame/components.dart';
+import 'package:flame_behaviors/flame_behaviors.dart';
+import 'package:trashy_road/gen/assets.gen.dart';
+import 'package:trashy_road/src/game/game.dart';
+
+export 'behaviors/behaviors.dart';
+
+class Bird extends PositionedEntity with ZIndex {
+  Bird._({required this.isFlyingRight, required this.speed})
+      : super(
+          scale: Vector2.all(0.5),
+          behaviors: [
+            BirdFlyingBehavior(),
+            BirdRandomSpawningBehavior(),
+            PausingBehavior<Bird>(
+              selector: (bird) => bird.findBehaviors<BirdFlyingBehavior>(),
+            ),
+          ],
+          children: [
+            GameSpriteAnimationComponent.fromPath(
+              spritePath: Assets.images.sprites.birdFlying.path,
+              animationData: SpriteAnimationData.sequenced(
+                amount: 25,
+                amountPerRow: 5,
+                textureSize: Vector2.all(128),
+                stepTime: 1 / 24,
+              ),
+            ),
+          ],
+        );
+
+  factory Bird.randomize() {
+    final isFlyingRight = random.nextBool();
+    final speed = minSpeed + random.nextDouble() * (maxSpeed - minSpeed);
+
+    return Bird._(isFlyingRight: isFlyingRight, speed: speed);
+  }
+
+  static List<Bird> randomAmount() {
+    final amountOfBirds = random.nextInt(maxAmountOfBirds + 1);
+
+    return List.generate(amountOfBirds, (_) => Bird.randomize());
+  }
+
+  static final random = Random();
+
+  /// The maximum amount of birds that are loaded into a map.
+  static const maxAmountOfBirds = 5;
+
+  static const maxSpeed = 3.0;
+  static const minSpeed = 1.0;
+
+  /// Whether the bird is flying right.
+  final bool isFlyingRight;
+
+  /// Speed Multiplier
+  final double speed;
+
+  @override
+  int get zIndex => 100000;
+}

packages/trashy_road/lib/src/game/entities/entities.dart

@@ -1,4 +1,5 @@
 export 'behaviors/behaviors.dart';
+export 'bird/bird.dart';
 export 'bus/bus.dart';
 export 'car/car.dart';
 export 'map_edge/map_edge.dart';