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

import 'dart:math';

import 'package:flame/collisions.dart';
import 'package:flame/components.dart';
import 'package:flame/events.dart';
import 'package:flame/extensions.dart';
import 'package:flame/game.dart';
import 'package:flame/palette.dart';
import 'package:flutter/material.dart' hide Image, Draggable;

enum Shapes { circle, rectangle, polygon }

class MultipleShapesExample extends FlameGame with HasCollisionDetection {
  static const description = '''
    An example with many hitboxes that move around on the screen and during
    collisions they change color depending on what it is that they have collided
    with. 
    
    The snowman, the component built with three circles on top of each other, 
    works a little bit differently than the other components to show that you
    can have multiple hitboxes within one component.
    
    On this example, you can "throw" the components by dragging them quickly in
    any direction.
  ''';

  MultipleShapesExample()
      : super(
          world: MultiShapesWorld(),
          camera: CameraComponent()..viewfinder.anchor = Anchor.topLeft,
        );
}

class MultiShapesWorld extends World with HasGameReference {
  @override
  Future<void> onLoad() async {
    add(FpsTextComponent(position: Vector2(0, game.size.y - 24)));
    final screenHitbox = ScreenHitbox();
    final snowman = CollidableSnowman(
      Vector2.all(150),
      Vector2(120, 250),
      Vector2(-100, 100),
      screenHitbox,
    );
    MyCollidable lastToAdd = snowman;
    add(screenHitbox);
    add(snowman);
    var totalAdded = 1;
    while (totalAdded < 1000) {
      lastToAdd = nextRandomCollidable(lastToAdd, screenHitbox);
      final lastBottomRight = lastToAdd.toAbsoluteRect().bottomRight;
      if (lastBottomRight.dx < game.size.x &&
          lastBottomRight.dy < game.size.y) {
        add(lastToAdd);
        totalAdded++;
      } else {
        break;
      }
    }
  }

  final _rng = Random();
  final _distance = Vector2(100, 0);

  MyCollidable nextRandomCollidable(
    MyCollidable lastCollidable,
    ScreenHitbox screenHitbox,
  ) {
    final collidableSize = Vector2.all(50) + Vector2.random(_rng) * 100;
    final isXOverflow = lastCollidable.position.x +
            lastCollidable.size.x / 2 +
            _distance.x +
            collidableSize.x >
        game.size.x;
    var position = _distance + Vector2(0, lastCollidable.position.y + 200);
    if (!isXOverflow) {
      position = (lastCollidable.position + _distance)
        ..x += collidableSize.x / 2;
    }
    final velocity = (Vector2.random(_rng) - Vector2.random(_rng)) * 400;
    return randomCollidable(
      position,
      collidableSize,
      velocity,
      screenHitbox,
      random: _rng,
    );
  }
}

abstract class MyCollidable extends PositionComponent
    with DragCallbacks, CollisionCallbacks, GestureHitboxes {
  double rotationSpeed = 0.0;
  final Vector2 velocity;
  final delta = Vector2.zero();
  double angleDelta = 0;
  final Color _defaultColor = Colors.blue.withValues(alpha: 0.8);
  final Color _collisionColor = Colors.green.withValues(alpha: 0.8);
  late final Paint _dragIndicatorPaint;
  final ScreenHitbox screenHitbox;
  ShapeHitbox? hitbox;

  MyCollidable(
    Vector2 position,
    Vector2 size,
    this.velocity,
    this.screenHitbox,
  ) : super(position: position, size: size, anchor: Anchor.center) {
    _dragIndicatorPaint = BasicPalette.white.paint();
  }

  @override
  void onMount() {
    hitbox?.paint.color = _defaultColor;
    super.onMount();
  }

  @override
  void update(double dt) {
    super.update(dt);
    if (isDragged) {
      return;
    }
    delta.setFrom(velocity * dt);
    position.add(delta);
    angleDelta = dt * rotationSpeed;
    angle = (angle + angleDelta) % (2 * pi);
    // Takes rotation into consideration (which topLeftPosition doesn't)
    final topLeft = absoluteCenter - (scaledSize / 2);
    if (topLeft.x + scaledSize.x < 0 ||
        topLeft.y + scaledSize.y < 0 ||
        topLeft.x > screenHitbox.scaledSize.x ||
        topLeft.y > screenHitbox.scaledSize.y) {
      final moduloSize = screenHitbox.scaledSize + scaledSize;
      topLeftPosition = topLeftPosition % moduloSize;
    }
  }

  @override
  void render(Canvas canvas) {
    if (isDragged) {
      final localCenter = scaledSize.toOffset() / 2;
      canvas.drawCircle(localCenter, 5, _dragIndicatorPaint);
    }
  }

  @override
  void onCollisionStart(
    Set<Vector2> intersectionPoints,
    PositionComponent other,
  ) {
    super.onCollisionStart(intersectionPoints, other);
    hitbox?.paint.color = _collisionColor;
  }

  @override
  void onCollisionEnd(PositionComponent other) {
    super.onCollisionEnd(other);
    if (!isColliding) {
      hitbox?.paint.color = _defaultColor;
    }
  }

  @override
  void onDragEnd(DragEndEvent event) {
    super.onDragEnd(event);
    velocity.setFrom(event.velocity / 10);
  }
}

class CollidablePolygon extends MyCollidable {
  CollidablePolygon(
    Vector2 position,
    Vector2 size,
    Vector2 velocity,
    ScreenHitbox screenHitbox,
  ) : super(position, size, velocity, screenHitbox) {
    hitbox = PolygonHitbox.relative(
      [
        Vector2(-1.0, 0.0),
        Vector2(-0.8, 0.6),
        Vector2(0.0, 1.0),
        Vector2(0.6, 0.9),
        Vector2(1.0, 0.0),
        Vector2(0.6, -0.8),
        Vector2(0, -1.0),
        Vector2(-0.8, -0.8),
      ],
      parentSize: size,
    )..renderShape = true;
    add(hitbox!);
  }
}

class CollidableRectangle extends MyCollidable {
  CollidableRectangle(
    super.position,
    super.size,
    super.velocity,
    super.screenHitbox,
  ) {
    hitbox = RectangleHitbox()..renderShape = true;
    add(hitbox!);
  }
}

class CollidableCircle extends MyCollidable {
  CollidableCircle(
    super.position,
    super.size,
    super.velocity,
    super.screenHitbox,
  ) {
    hitbox = CircleHitbox()..renderShape = true;
    add(hitbox!);
  }
}

class SnowmanPart extends CircleHitbox {
  @override
  final renderShape = true;
  final startColor = Colors.white.withValues(alpha: 0.8);
  final Color hitColor;

  SnowmanPart(double radius, Vector2 position, this.hitColor)
      : super(radius: radius, position: position, anchor: Anchor.center) {
    paint.color = startColor;
  }

  @override
  void onCollisionStart(Set<Vector2> intersectionPoints, ShapeHitbox other) {
    super.onCollisionStart(intersectionPoints, other);

    if (other.hitboxParent is ScreenHitbox) {
      paint.color = startColor;
    } else {
      paint.color = hitColor.withValues(alpha: 0.8);
    }
  }

  @override
  void onCollisionEnd(ShapeHitbox other) {
    super.onCollisionEnd(other);
    if (!isColliding) {
      paint.color = startColor;
    }
  }
}

class CollidableSnowman extends MyCollidable {
  CollidableSnowman(
    Vector2 position,
    Vector2 size,
    Vector2 velocity,
    ScreenHitbox screenHitbox,
  ) : super(position, size, velocity, screenHitbox) {
    rotationSpeed = 0.3;
    anchor = Anchor.topLeft;
    final top = SnowmanPart(
      size.x * 0.3,
      Vector2(size.x / 2, size.y * 0.15),
      Colors.red,
    );
    final middle = SnowmanPart(
      size.x * 0.4,
      Vector2(size.x / 2, size.y * 0.4),
      Colors.yellow,
    );
    final bottom = SnowmanPart(
      size.x / 2,
      Vector2(size.x / 2, size.y - size.y / 4),
      Colors.green,
    );
    add(bottom);
    add(middle);
    add(top);
  }
}

MyCollidable randomCollidable(
  Vector2 position,
  Vector2 size,
  Vector2 velocity,
  ScreenHitbox screenHitbox, {
  Random? random,
}) {
  final rng = random ?? Random();
  final rotationSpeed = 0.5 - rng.nextDouble();
  final shapeType = Shapes.values[rng.nextInt(Shapes.values.length)];
  return switch (shapeType) {
    Shapes.circle => CollidableCircle(position, size, velocity, screenHitbox)
      ..rotationSpeed = rotationSpeed,
    Shapes.rectangle =>
      CollidableRectangle(position, size, velocity, screenHitbox)
        ..rotationSpeed = rotationSpeed,
    Shapes.polygon => CollidablePolygon(position, size, velocity, screenHitbox)
      ..rotationSpeed = rotationSpeed,
  };
}