是否可以用Dart / Flutter绘制图像?
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我正在寻找一个从颤振应用程序中生成图像(jpeg或png)的路径。图像将由圆,线,文本等组成。
似乎有一种使用画布(https://docs.flutter.io/flutter/dart-ui/Canvas/Canvas.html)绘制到屏幕的方法,但是似乎没有相应的用于创建可以在应用程序内部呈现或发送/使用的图像。
有没有可用于绘制图像的dart库?似乎可以给出底层的skia框架。在Dart-html包中有一个CanvasRenderingContext2D。
编辑:获得类似下面的工作(根据理查德的建议)将是一个开始:
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'dart:ui';
import 'dart:typed_data';
import 'dart:async';
import 'dart:io';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
Image _image;
@override
void initState() {
super.initState();
_image = new Image.network(
'https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_120x44dp.png',
);
}
Future<String> get _localPath async {
final directory =
await getApplicationDocumentsDirectory(); //From path_provider package
return directory.path;
}
Future<File> get _localFile async {
final path = await _localPath;
return new File('$path/tempImage.png');
}
Future<File> writeImage(ByteData pngBytes) async {
final file = await _localFile;
// Write the file
file.writeAsBytes(pngBytes.buffer.asUint8List());
return file;
}
_generateImage() {
_generate().then((val) => setState(() {
_image = val;
}));
}
Future<Image> _generate() async {
PictureRecorder recorder = new PictureRecorder();
Canvas c = new Canvas(recorder);
var rect = new Rect.fromLTWH(0.0, 0.0, 100.0, 100.0);
c.clipRect(rect);
final paint = new Paint();
paint.strokeWidth = 2.0;
paint.color = const Color(0xFF333333);
paint.style = PaintingStyle.fill;
final offset = new Offset(50.0, 50.0);
c.drawCircle(offset, 40.0, paint);
var picture = recorder.endRecording();
final pngBytes =
await picture.toImage(100, 100).toByteData(format: ImageByteFormat.png);
//Aim #1. Upade _image with generated image.
var image = Image.memory(pngBytes.buffer.asUint8List());
return image;
//new Image.memory(pngBytes.buffer.asUint8List());
// _image = new Image.network(
// 'https://github.com/flutter/website/blob/master/_includes/code/layout/lakes/images/lake.jpg?raw=true',
// );
//Aim #2. Write image to file system.
//writeImage(pngBytes);
//Make a temporary file (see elsewhere on SO) and writeAsBytes(pngBytes.buffer.asUInt8List())
}
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: new Center(
child: new Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
_image,
],
),
),
floatingActionButton: new FloatingActionButton(
onPressed: _generateImage,
tooltip: 'Generate',
child: new Icon(Icons.add),
),
);
}
}
答案
PictureRecorder
允许你创建一个Canvas,使用Canvas绘图方法并提供endRecording()
返回Picture
。您可以将此图片绘制到其他场景或画布,或使用.toImage(width, height).toByteData(format)
将其转换为PNG(或原始 - 不支持jpeg)。
例如:
import 'dart:ui';
import 'dart:typed_data';
....
PictureRecorder recorder = new PictureRecorder();
Canvas c = new Canvas(recorder);
c.drawPaint(paint); // etc
Picture p = recorder.endRecording();
ByteData pngBytes =
await p.toImage(100, 100).toByteData(format: ImageByteFormat.png);
确保你处于颤振0.4.4,否则你可能没有format
参数。
但是,看过你的编辑后,我怀疑你真的在寻找CustomPainter
,其中一个Widget为你提供了一个可以绘制画布的画布。这是来自类似问题的example。
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