gestures.dart 7.23 KB
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// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

class ScaleApp extends StatefulComponent {
  ScaleAppState createState() => new ScaleAppState();
}

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class _GesturePainter extends CustomPainter {
  const _GesturePainter({
    this.zoom,
    this.offset,
    this.swatch,
    this.forward,
    this.scaleEnabled,
    this.tapEnabled,
    this.doubleTapEnabled,
    this.longPressEnabled
  });

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  final double zoom;
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  final Offset offset;
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  final Map<int, Color> swatch;
  final bool forward;
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  final bool scaleEnabled;
  final bool tapEnabled;
  final bool doubleTapEnabled;
  final bool longPressEnabled;

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  void paint(Canvas canvas, Size size) {
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    Point center = (size.center(Point.origin).toOffset() * zoom + offset).toPoint();
    double radius = size.width / 2.0 * zoom;
    Gradient gradient = new RadialGradient(
      center: center, radius: radius,
      colors: forward ? <Color>[swatch[50], swatch[900]]
                      : <Color>[swatch[900], swatch[50]]
    );
    Paint paint = new Paint()
      ..shader = gradient.createShader();
    canvas.drawCircle(center, radius, paint);
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  }
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  bool shouldRepaint(_GesturePainter oldPainter) {
    return oldPainter.zoom != zoom
        || oldPainter.offset != offset
        || oldPainter.swatch != swatch
        || oldPainter.forward != forward
        || oldPainter.scaleEnabled != scaleEnabled
        || oldPainter.tapEnabled != tapEnabled
        || oldPainter.doubleTapEnabled != doubleTapEnabled
        || oldPainter.longPressEnabled != longPressEnabled;
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  }
}

class ScaleAppState extends State<ScaleApp> {

  Point _startingFocalPoint;

  Offset _previousOffset;
  Offset _offset = Offset.zero;

  double _previousZoom;
  double _zoom = 1.0;

  Map<int, Color> _swatch = Colors.blue;

  bool _forward = true;
  bool _scaleEnabled = true;
  bool _tapEnabled = true;
  bool _doubleTapEnabled = true;
  bool _longPressEnabled = true;

  void _handleScaleStart(Point focalPoint) {
    setState(() {
      _startingFocalPoint = focalPoint;
      _previousOffset = _offset;
      _previousZoom = _zoom;
    });
  }

  void _handleScaleUpdate(double scale, Point focalPoint) {
    setState(() {
      _zoom = (_previousZoom * scale);

      // Ensure that item under the focal point stays in the same place despite zooming
      Offset normalizedOffset = (_startingFocalPoint.toOffset() - _previousOffset) / _previousZoom;
      _offset = focalPoint.toOffset() - normalizedOffset * _zoom;
    });
  }

  void _handleScaleReset() {
    setState(() {
      _zoom = 1.0;
      _offset = Offset.zero;
    });
  }

  void _handleColorChange() {
    setState(() {
      switch (_swatch) {
        case Colors.blueGrey:   _swatch = Colors.red; break;
        case Colors.red:        _swatch = Colors.pink; break;
        case Colors.pink:       _swatch = Colors.purple; break;
        case Colors.purple:     _swatch = Colors.deepPurple; break;
        case Colors.deepPurple: _swatch = Colors.indigo; break;
        case Colors.indigo:     _swatch = Colors.blue; break;
        case Colors.blue:       _swatch = Colors.lightBlue; break;
        case Colors.lightBlue:  _swatch = Colors.cyan; break;
        case Colors.cyan:       _swatch = Colors.teal; break;
        case Colors.teal:       _swatch = Colors.green; break;
        case Colors.green:      _swatch = Colors.lightGreen; break;
        case Colors.lightGreen: _swatch = Colors.lime; break;
        case Colors.lime:       _swatch = Colors.yellow; break;
        case Colors.yellow:     _swatch = Colors.amber; break;
        case Colors.amber:      _swatch = Colors.orange; break;
        case Colors.orange:     _swatch = Colors.deepOrange; break;
        case Colors.deepOrange: _swatch = Colors.brown; break;
        case Colors.brown:      _swatch = Colors.grey; break;
        case Colors.grey:       _swatch = Colors.blueGrey; break;
        default:                assert(false);
      }
    });
  }

  void _handleDirectionChange() {
    setState(() {
      _forward = !_forward;
    });
  }


  Widget build(BuildContext context) {
    return new Theme(
      data: new ThemeData.dark(),
      child: new Scaffold(
        toolBar: new ToolBar(
            center: new Text('Gestures Demo')),
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        body: new Stack(
          children: <Widget>[
            new GestureDetector(
              onScaleStart: _scaleEnabled ? _handleScaleStart : null,
              onScaleUpdate: _scaleEnabled ? _handleScaleUpdate : null,
              onTap: _tapEnabled ? _handleColorChange : null,
              onDoubleTap: _doubleTapEnabled ? _handleScaleReset : null,
              onLongPress: _longPressEnabled ? _handleDirectionChange : null,
              child: new CustomPaint(
                painter: new _GesturePainter(
                  zoom: _zoom,
                  offset: _offset,
                  swatch: _swatch,
                  forward: _forward,
                  scaleEnabled: _scaleEnabled,
                  tapEnabled: _tapEnabled,
                  doubleTapEnabled: _doubleTapEnabled,
                  longPressEnabled: _longPressEnabled
                )
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              )
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            ),
            new Positioned(
              bottom: 0.0,
              left: 0.0,
              child: new Card(
                child: new Container(
                  padding: new EdgeDims.all(4.0),
                  child: new Column(
                    children: <Widget>[
                      new Row(
                        children: <Widget>[
                          new Checkbox(
                            value: _scaleEnabled,
                            onChanged: (bool value) { setState(() { _scaleEnabled = value; }); }
                          ),
                          new Text('Scale'),
                        ]
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                      ),
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                      new Row(
                        children: <Widget>[
                          new Checkbox(
                            value: _tapEnabled,
                            onChanged: (bool value) { setState(() { _tapEnabled = value; }); }
                          ),
                          new Text('Tap'),
                        ]
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                      ),
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                      new Row(
                        children: <Widget>[
                          new Checkbox(
                            value: _doubleTapEnabled,
                            onChanged: (bool value) { setState(() { _doubleTapEnabled = value; }); }
                          ),
                          new Text('Double Tap'),
                        ]
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                      ),
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                      new Row(
                        children: <Widget>[
                          new Checkbox(
                            value: _longPressEnabled,
                            onChanged: (bool value) { setState(() { _longPressEnabled = value; }); }
                          ),
                          new Text('Long Press'),
                        ]
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                      ),
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                    ],
                    alignItems: FlexAlignItems.start
                  )
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                )
              )
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            ),
          ]
        )
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      )
    );
  }
}

void main() => runApp(new ScaleApp());