flame/docs/examples/gestures/lib/main_multitap_advanced.dart

import 'package:flutter/material.dart';
import 'package:flame/game.dart';
import 'package:flame/gestures.dart';

void main() {
  final game = MyGame();
  runApp(game.widget);
}

/// Includes an example mixing basic and advanced detectors
class MyGame extends Game with MultiTouchTapDetector, PanDetector {
  final _whitePaint = Paint()..color = const Color(0xFFFFFFFF);

  Paint _paint;

  final Map<int, Rect> _taps = {};

  Offset _start;
  Offset _end;
  Rect _panRect;

  MyGame() {
    _paint = _whitePaint;
  }

  @override
  void onTapDown(int pointerId, TapDownDetails details) {
    _taps[pointerId] = Rect.fromLTWH(
        details.globalPosition.dx, details.globalPosition.dy, 50, 50);
  }

  @override
  void onTapUp(int pointerId, _) {
    _taps.remove(pointerId);
  }

  @override
  void onTapCancel(int pointerId) {
    _taps.remove(pointerId);
  }

  @override
  void onPanStart(details) {
    _end = null;
    _start = details.localPosition;
  }

  @override
  void onPanUpdate(details) {
    _end = details.localPosition;
  }

  @override
  void onPanEnd(details) {
    _panRect = Rect.fromLTRB(
      _start.dx,
      _start.dy,
      _end.dx,
      _end.dy,
    );
  }

  @override
  void update(double dt) {}

  @override
  void render(Canvas canvas) {
    _taps.values.forEach((rect) {
      canvas.drawRect(rect, _paint);
    });

    if (_panRect != null) {
      canvas.drawRect(_panRect, _paint);
    }
  }
}