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

import 'dart:ui';

import 'package:flame/components.dart';
import 'package:flame/extensions.dart';
import 'package:flame/game.dart';
import 'package:flame/geometry.dart';
import 'package:flame/gestures.dart';
import 'package:flutter/material.dart' hide Image, Draggable;

class MyCollidable extends PositionComponent
    with HasGameRef<Circles>, Hitbox, Collidable {
  late Vector2 velocity;
  final _collisionColor = Colors.amber;
  final _defaultColor = Colors.cyan;
  bool _isWallHit = false;
  bool _isCollision = false;

  MyCollidable(Vector2 position)
      : super(
          position: position,
          size: Vector2.all(100),
          anchor: Anchor.center,
        ) {
    addShape(HitboxCircle());
  }

  @override
  Future<void> onLoad() async {
    final center = gameRef.size / 2;
    velocity = (center - position)..scaleTo(150);
  }

  @override
  void update(double dt) {
    super.update(dt);
    if (_isWallHit) {
      remove();
      return;
    }
    debugColor = _isCollision ? _collisionColor : _defaultColor;
    position.add(velocity * dt);
    _isCollision = false;
  }

  @override
  void render(Canvas canvas) {
    super.render(canvas);
    renderShapes(canvas);
  }

  @override
  void onCollision(Set<Vector2> intersectionPoints, Collidable other) {
    if (other is ScreenCollidable) {
      _isWallHit = true;
      return;
    }
    _isCollision = true;
  }
}

class Circles extends BaseGame with HasCollidables, TapDetector {
  @override
  Future<void> onLoad() async {
    add(ScreenCollidable());
  }

  @override
  void onTapDown(TapDownInfo event) {
    add(MyCollidable(event.eventPosition.game));
  }
}