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@override |
widget build(BuildContext context) { |
return scaffold( |
appBar: AppBar( |
title: text(widget.title), |
), |
body: center( |
child: FadeTransition( |
opacity: curve, |
child: const FlutterLogo( |
size: 100, |
), |
), |
), |
floatingActionButton: FloatingActionButton( |
tooltip: 'fade', |
onPressed: () { |
controller.forward(); |
}, |
child: const Icon(Icons.brush), |
), |
); |
} |
} |
<code_end> |
for more information, see |
animation & motion widgets, |
the animations tutorial, |
and the animations overview. |
<topic_end> |
<topic_start> |
how do i use a canvas to draw/paint? |
in android, you would use the canvas and drawable |
to draw images and shapes to the screen. |
flutter has a similar canvas API as well, |
since it鈥檚 based on the same low-level rendering engine, skia. |
as a result, painting to a canvas in flutter |
is a very familiar task for android developers. |
flutter has two classes that help you draw to the canvas: CustomPaint |
and CustomPainter, |
the latter of which implements your algorithm to draw to the canvas. |
to learn how to implement a signature painter in flutter, |
see collin鈥檚 answer on custom paint. |
<code_start> |
import 'package:flutter/material.dart'; |
void main() => runApp(const MaterialApp(home: DemoApp())); |
class DemoApp extends StatelessWidget { |
const DemoApp({super.key}); |
@override |
widget build(BuildContext context) => const scaffold(body: signature()); |
} |
class signature extends StatefulWidget { |
const signature({super.key}); |
@override |
SignatureState createState() => SignatureState(); |
} |
class SignatureState extends State<Signature> { |
List<Offset?> _points = <offset>[]; |
@override |
widget build(BuildContext context) { |
return GestureDetector( |
onPanUpdate: (details) { |
setState(() { |
RenderBox? referenceBox = context.findRenderObject() as RenderBox; |
offset localPosition = |
referenceBox.globalToLocal(details.globalPosition); |
_points = List.from(_points)..add(localPosition); |
}); |
}, |
onPanEnd: (details) => _points.add(null), |
child: CustomPaint( |
painter: SignaturePainter(_points), |
size: size.infinite, |
), |
); |
} |
} |
class SignaturePainter extends CustomPainter { |
SignaturePainter(this.points); |
final List<Offset?> points; |
@override |
void paint(Canvas canvas, size size) { |
var paint = paint() |
..color = colors.black |
..strokeCap = StrokeCap.round |
..strokeWidth = 5; |
for (int i = 0; i < points.length - 1; i++) { |
if (points[i] != null && points[i + 1] != null) { |
canvas.drawLine(points[i]!, points[i + 1]!, paint); |
} |
} |
} |
@override |
bool shouldRepaint(SignaturePainter oldDelegate) => |
oldDelegate.points != points; |
} |
<code_end> |
<topic_end> |
<topic_start> |
how do i build custom widgets? |