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

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

import 'package:flame/components.dart';
import 'package:flame/effects.dart';
import 'package:flame/game.dart';
import 'package:flame/geometry.dart';
import 'package:flame/input.dart';
import 'package:flame/palette.dart';

enum Shapes { circle, rectangle, polygon }

class SimpleShapesExample extends FlameGame with HasTappables {
  static const description = '''
    An example which adds random shapes on the screen when you tap it, if you
    tap on an already existing shape it will remove that shape and replace it
    with a new one.
  ''';

  final _rng = Random();

  MyShapeComponent randomShape(Vector2 position) {
    final shapeType = Shapes.values[_rng.nextInt(Shapes.values.length)];
    final shapeSize =
        Vector2.all(100) + Vector2.all(50.0).scaled(_rng.nextDouble());
    final shapeAngle = _rng.nextDouble() * 6;
    switch (shapeType) {
      case Shapes.circle:
        return MyShapeComponent(
          HitboxCircle(),
          position: position,
          size: shapeSize,
          angle: shapeAngle,
        );
      case Shapes.rectangle:
        return MyShapeComponent(
          HitboxRectangle(),
          position: position,
          size: shapeSize,
          angle: shapeAngle,
        );
      case Shapes.polygon:
        final points = [
          Vector2.random(_rng),
          Vector2.random(_rng)..y *= -1,
          -Vector2.random(_rng),
          Vector2.random(_rng)..x *= -1,
        ];
        return MyShapeComponent(
          HitboxPolygon(points),
          position: position,
          size: shapeSize,
          angle: shapeAngle,
        );
    }
  }

  @override
  void onTapDown(int pointerId, TapDownInfo info) {
    super.onTapDown(pointerId, info);
    final tapPosition = info.eventPosition.game;
    final component = randomShape(tapPosition);
    add(component);
    component.add(
      MoveEffect.to(
        size / 2,
        EffectController(
          duration: 5,
          reverseDuration: 5,
          infinite: true,
        ),
      ),
    );
    component.add(
      RotateEffect.to(
        3,
        EffectController(
          duration: 1,
          reverseDuration: 1,
          infinite: true,
        ),
      ),
    );
  }
}

class MyShapeComponent extends ShapeComponent with Tappable {
  @override
  final Paint paint = BasicPalette.red.paint()..style = PaintingStyle.stroke;

  MyShapeComponent(
    HitboxShape shape, {
    Vector2? position,
    Vector2? size,
    double? angle,
  }) : super(
          shape,
          position: position,
          size: size,
          angle: angle,
          anchor: Anchor.center,
        );

  @override
  bool onTapDown(TapDownInfo _) {
    removeFromParent();
    return true;
  }
}