如何在 Flutter 中从画布上裁剪圆形(或方形或六边形)区域 [英] How to crop circular(or Square or Hexagon ) area from canvas in Flutter

问题描述

我想裁剪一个矩形图像文件，使其成为圆形、正方形或六边形，然后将其保存为本地图像文件.我有一个位图，我想从这个位图中裁剪一个圆形或六边形区域.圆圈外的所有像素都应该是透明的.我该怎么做?

我在

将图像画布保存为 png

完整源代码:

 导入 'dart:io';导入包:颤振/material.dart"；导入 'dart:ui' 作为 ui；导入 'package:flutter/services.dart' 显示 rootBundle；导入飞镖:异步"；导入'dart:typed_data'；导入飞镖:数学"作为数学；导入包:路径/path.dart"；导入'包:path_provider/path_provider.dart'；类 CustomImageCanvas 扩展 StatefulWidget {CustomImageCanvas({Key key, this.title}) : super(key: key);最终字符串标题；@覆盖_CustomImageCanvasState createState() =>_CustomImageCanvasState();}类 _CustomImageCanvasState 扩展状态<CustomImageCanvas>{ui.Image图像；布尔 isImageloaded = false;无效初始化状态(){super.initState();在里面();}未来<空>初始化()异步{最终 ByteData 数据 = 等待 rootBundle.load('assets/image.jpeg');图像 = 等待 loadImage(Uint8List.view(data.buffer));}未来<ui.Image>loadImage(Listimg) 异步 {最终完成者<ui.Image>完成者 = 完成者()；ui.decodeImageFromList(img, (ui.Image img) {设置状态((){isImageloaded = true;});返回完成者.完成(img)；});返回完成者.future；}小部件 _buildImage() {如果(this.isImageloaded){返回自定义油漆(画家:PngImagePainter(图像:图像)，);} 别的 {返回中心(子:文本('正在加载'))；}}@覆盖小部件构建(BuildContext 上下文){返回脚手架(应用栏:应用栏(标题:文本(widget.title)，),身体:容器(孩子:_buildImage()，));}}类 PngImagePainter 扩展 CustomPainter {PngImagePainter({这个图片，});ui.Image图像；@覆盖无效油漆(帆布画布，尺寸大小){_drawCanvas(大小，画布)；_saveCanvas(大小);}画布_drawCanvas(大小，画布画布){最终中心 = 偏移量(150, 50)；最终半径 = math.min(size.width, size.height)/8;//圆圈应该在之前绘制，否则它会被路径隐藏油漆paintCircle = Paint()..color = Colors.black;绘制paintBorder = Paint()..color = 颜色.white..strokeWidth = size.width/36..style = 绘画风格.stroke;canvas.drawCircle(中心，半径，paintCircle)；canvas.drawCircle(中心，半径，paintBorder)；双drawImageWidth = 0;var drawImageHeight = -size.height * 0.8;路径 path = Path()..addOval(Rect.fromLTWH(drawImageWidth, drawImageHeight,image.width.toDouble(), image.height.toDouble()));canvas.clipPath(路径);canvas.drawImage(图像，偏移量(drawImageWidth，drawImageHeight)，Paint())；返回画布；}_saveCanvas(大小)异步{var pictureRecorder = ui.PictureRecorder();var canvas = Canvas(pictureRecorder);var 油漆 = 油漆()；paint.isAntiAlias = true;_drawCanvas(大小，画布)；var pic = pictureRecorder.endRecording();ui.Image img = await pic.toImage(image.width, image.height);var byteData = await img.toByteData(格式: ui.ImageByteFormat.png);var buffer = byteData.buffer.asUint8List();//var response = await get(imgUrl);var documentDirectory = 等待 getApplicationDocumentsDirectory();文件 file = File(join(documentDirectory.path,'${DateTime.now().toUtc().toIso8601String()}.png'));file.writeAsBytesSync(缓冲区)；打印(文件.路径)；}@覆盖bool shouldRepaint(CustomPainter oldDelegate) {返回假；}}

I want to crop a rectangular image-file and make it circular or square or hexagon shape and save it as image-file locally. I have a bitmap and I want to crop a circular or hexagon region from this bitmap. All pixels outside the circle should be transparent. How can I do this?

I found the similar question in android platform. But unable to find a good resource that really help or direct me to achieve this in flutter. Please share me the idea to achieve this result.

解决方案

These simple steps get the required result.

1. Create a PictureRecorder.
2. Create a Canvas with your PictureRecorder.
3. Draw circle in canvas using canvas.drawCircle().
4. Call endRecording() on the PictureRecorder to get a Picture.
5. Call toImage() on the Picture.
6. Convert image toByteData() .
7. Save image locally using getApplicationDocumentsDirectory().

Canvas Screen

Saved Image Canvas as png

Full Source Code:

        import 'dart:io';

        import 'package:flutter/material.dart';
        import 'dart:ui' as ui;
        import 'package:flutter/services.dart' show rootBundle;
        import 'dart:async';
        import 'dart:typed_data';
        import 'dart:math' as math;
        import 'package:path/path.dart';
        import 'package:path_provider/path_provider.dart';

        class CustomImageCanvas extends StatefulWidget {
          CustomImageCanvas({Key key, this.title}) : super(key: key);

          final String title;

          @override
          _CustomImageCanvasState createState() => _CustomImageCanvasState();
        }

        class _CustomImageCanvasState extends State<CustomImageCanvas> {
          ui.Image image;
          bool isImageloaded = false;
          void initState() {
            super.initState();
            init();
          }

          Future<Null> init() async {
            final ByteData data = await rootBundle.load('assets/image.jpeg');
            image = await loadImage(Uint8List.view(data.buffer));
          }

          Future<ui.Image> loadImage(List<int> img) async {
            final Completer<ui.Image> completer = Completer();
            ui.decodeImageFromList(img, (ui.Image img) {
              setState(() {
                isImageloaded = true;
              });
              return completer.complete(img);
            });
            return completer.future;
          }

          Widget _buildImage() {
            if (this.isImageloaded) {
              return CustomPaint(
                painter: PngImagePainter(image: image),
              );
            } else {
              return Center(child: Text('loading'));
            }
          }

          @override
          Widget build(BuildContext context) {
            return Scaffold(
                appBar: AppBar(
                  title: Text(widget.title),
                ),
                body: Container(
                  child: _buildImage(),
                ));
          }
        }

        class PngImagePainter extends CustomPainter {
          PngImagePainter({
            this.image,
          });

          ui.Image image;

          @override
          void paint(Canvas canvas, Size size) {
            _drawCanvas(size, canvas);
            _saveCanvas(size);
          }

          Canvas _drawCanvas(Size size, Canvas canvas) {
            final center = Offset(150, 50);
            final radius = math.min(size.width, size.height) / 8;

            // The circle should be paint before or it will be hidden by the path
            Paint paintCircle = Paint()..color = Colors.black;
            Paint paintBorder = Paint()
              ..color = Colors.white
              ..strokeWidth = size.width / 36
              ..style = PaintingStyle.stroke;
            canvas.drawCircle(center, radius, paintCircle);
            canvas.drawCircle(center, radius, paintBorder);

            double drawImageWidth = 0;
            var drawImageHeight = -size.height * 0.8;

            Path path = Path()
              ..addOval(Rect.fromLTWH(drawImageWidth, drawImageHeight,
                  image.width.toDouble(), image.height.toDouble()));

            canvas.clipPath(path);

            canvas.drawImage(image, Offset(drawImageWidth, drawImageHeight), Paint());
            return canvas;
          }

          _saveCanvas(Size size) async {
            var pictureRecorder = ui.PictureRecorder();
            var canvas = Canvas(pictureRecorder);
            var paint = Paint();
            paint.isAntiAlias = true;

            _drawCanvas(size, canvas);

            var pic = pictureRecorder.endRecording();
            ui.Image img = await pic.toImage(image.width, image.height);
            var byteData = await img.toByteData(format: ui.ImageByteFormat.png);
            var buffer = byteData.buffer.asUint8List();

            // var response = await get(imgUrl);
            var documentDirectory = await getApplicationDocumentsDirectory();
            File file = File(join(documentDirectory.path,
                '${DateTime.now().toUtc().toIso8601String()}.png'));
            file.writeAsBytesSync(buffer);

            print(file.path);
          }

          @override
          bool shouldRepaint(CustomPainter oldDelegate) {
            return false;
          }
        }

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