flame/examples/lib/stories/collision_detection/collidable_animation_example.dart

import 'dart:math';
import 'dart:ui';

import 'package:flame/collisions.dart';
import 'package:flame/components.dart';
import 'package:flame/game.dart';
import 'package:flame/palette.dart';

class CollidableAnimationExample extends FlameGame with HasCollisionDetection {
  static const description = '''
    In this example you can see four animated birds which are flying straight
    along the same route until they hit either another bird or the wall, which
    makes them turn. The birds have PolygonHitboxes which are marked with the
    white lines.
  ''';

  @override
  Future<void> onLoad() async {
    add(ScreenHitbox());
    final componentSize = Vector2(150, 100);
    // Top left component
    add(
      AnimatedComponent(Vector2.all(200), Vector2.all(100), componentSize)
        ..flipVertically(),
    );
    // Bottom right component
    add(
      AnimatedComponent(
        Vector2(-100, -100),
        size.clone()..sub(Vector2.all(200)),
        componentSize / 2,
      ),
    );
    // Bottom left component
    add(
      AnimatedComponent(
        Vector2(100, -100),
        Vector2(100, size.y - 100),
        componentSize * 1.5,
        angle: pi / 4,
      ),
    );
    // Top right component
    add(
      AnimatedComponent(
        Vector2(-300, 300),
        Vector2(size.x - 100, 100),
        componentSize / 3,
        angle: pi / 4,
      )..flipVertically(),
    );
  }
}

class AnimatedComponent extends SpriteAnimationComponent
    with CollisionCallbacks, HasGameRef {
  final Vector2 velocity;

  AnimatedComponent(
    this.velocity,
    Vector2 position,
    Vector2 size, {
    double angle = -pi / 4,
  }) : super(
          position: position,
          size: size,
          angle: angle,
          anchor: Anchor.center,
        );

  @override
  Future<void> onLoad() async {
    animation = await gameRef.loadSpriteAnimation(
      'bomb_ptero.png',
      SpriteAnimationData.sequenced(
        amount: 4,
        stepTime: 0.2,
        textureSize: Vector2.all(48),
      ),
    );
    final hitboxPaint = BasicPalette.white.paint()
      ..style = PaintingStyle.stroke;
    add(
      PolygonHitbox.relative(
        [
          Vector2(0.0, -1.0),
          Vector2(-1.0, -0.1),
          Vector2(-0.2, 0.4),
          Vector2(0.2, 0.4),
          Vector2(1.0, -0.1),
        ],
        parentSize: size,
      )
        ..paint = hitboxPaint
        ..renderShape = true,
    );
  }

  @override
  void update(double dt) {
    super.update(dt);
    position += velocity * dt;
  }

  final Paint hitboxPaint = BasicPalette.green.paint()
    ..style = PaintingStyle.stroke;
  final Paint dotPaint = BasicPalette.red.paint()..style = PaintingStyle.stroke;

  @override
  void onCollisionStart(
    Set<Vector2> intersectionPoints,
    PositionComponent other,
  ) {
    super.onCollisionStart(intersectionPoints, other);
    velocity.negate();
    flipVertically();
  }
}