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TwoFingerScrollDetector
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| import 'dart:math'; | |
| import 'package:flutter/gestures.dart'; | |
| import 'package:flutter/material.dart'; | |
| enum ScrollDirection { up, down, left, right, none } | |
| typedef TwoFingerScrollCallback = | |
| void Function(ScrollDirection direction, double speed, Offset delta); | |
| class TwoFingerScrollDetector extends StatefulWidget { | |
| final Widget child; | |
| final TwoFingerScrollCallback onScroll; | |
| const TwoFingerScrollDetector({ | |
| super.key, | |
| required this.child, | |
| required this.onScroll, | |
| }); | |
| @override | |
| State<TwoFingerScrollDetector> createState() => _TwoFingerScrollDetectorState(); | |
| } | |
| class _TwoFingerScrollDetectorState extends State<TwoFingerScrollDetector> { | |
| int _touchPointers = 0; | |
| Offset? _lastPoint; | |
| late DateTime _lastTime; | |
| ScrollDirection _dirFromDelta(Offset delta) { | |
| if (delta.dx == 0 && delta.dy == 0) return ScrollDirection.none; | |
| if (delta.dy.abs() > delta.dx.abs()) { | |
| return delta.dy < 0 ? ScrollDirection.up : ScrollDirection.down; | |
| } else { | |
| return delta.dx < 0 ? ScrollDirection.left : ScrollDirection.right; | |
| } | |
| } | |
| double _speed(Offset delta, Duration dt) { | |
| if (dt.inMicroseconds == 0) return 0; | |
| return delta.distance / (dt.inMicroseconds / 1e6); | |
| } | |
| @override | |
| Widget build(BuildContext context) { | |
| return Listener( | |
| // mouse/trackpad scroll | |
| onPointerSignal: (signal) { | |
| if (signal is PointerScrollEvent) { | |
| final delta = signal.scrollDelta; | |
| final direction = _dirFromDelta(delta); | |
| final speed = delta.distance * 60; // approx px/s on desktop | |
| widget.onScroll(direction, speed, delta); | |
| } | |
| }, | |
| // touch tracking (for physical two-finger gestures) | |
| onPointerDown: (_) => _touchPointers++, | |
| onPointerUp: (_) { | |
| _touchPointers = max(0, _touchPointers - 1); | |
| _lastPoint = null; | |
| }, | |
| onPointerCancel: (_) { | |
| _touchPointers = max(0, _touchPointers - 1); | |
| _lastPoint = null; | |
| }, | |
| behavior: HitTestBehavior.opaque, | |
| child: GestureDetector( | |
| onScaleStart: (details) { | |
| if (_touchPointers == 2) { | |
| _lastPoint = details.focalPoint; | |
| _lastTime = DateTime.now(); | |
| } | |
| }, | |
| onScaleUpdate: (details) { | |
| if (_touchPointers != 2) return; | |
| final now = DateTime.now(); | |
| final dt = now.difference(_lastTime); | |
| final last = _lastPoint ?? details.focalPoint; | |
| final delta = details.focalPoint - last; | |
| final direction = _dirFromDelta(delta); | |
| final speed = _speed(delta, dt); | |
| widget.onScroll(direction, speed, delta); | |
| _lastPoint = details.focalPoint; | |
| _lastTime = now; | |
| }, | |
| onScaleEnd: (_) { | |
| widget.onScroll(ScrollDirection.none, 0, Offset.zero); | |
| }, | |
| child: widget.child, | |
| ), | |
| ); | |
| } | |
| } | |
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