如何在 Flutter 中从画布上裁剪圆形(或方形或六边形)区域

本文介绍了如何在 Flutter 中从画布上裁剪圆形(或方形或六边形)区域的处理方法,对大家解决问题具有一定的参考价值

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(drawImageWidthdrawImageHeight),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;
          }
        }

这篇关于如何在 Flutter 中从画布上裁剪圆形(或方形或六边形)区域的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,WP2

admin_action_{$_REQUEST[‘action’]}

do_action( "admin_action_{$_REQUEST[‘action’]}" )动作钩子::在发送“Action”请求变量时激发。Action Hook: Fires when an ‘action’ request variable is sent.目录锚点:#说明#源码说明(Description)钩子名称的动态部分$_REQUEST['action']引用从GET或POST请求派生的操作。源码(Source)更新版本源码位置使用被使用2.6.0 wp-admin/admin.php:...

日期:2020-09-02 17:44:16 浏览:1127

admin_footer-{$GLOBALS[‘hook_suffix’]}

do_action( "admin_footer-{$GLOBALS[‘hook_suffix’]}", string $hook_suffix )操作挂钩:在默认页脚脚本之后打印脚本或数据。Action Hook: Print scripts or data after the default footer scripts.目录锚点:#说明#参数#源码说明(Description)钩子名的动态部分,$GLOBALS['hook_suffix']引用当前页的全局钩子后缀。参数(Parameters)参数类...

日期:2020-09-02 17:44:20 浏览:1032

customize_save_{$this->id_data[‘base’]}

do_action( "customize_save_{$this-&gt;id_data[‘base’]}", WP_Customize_Setting $this )动作钩子::在调用WP_Customize_Setting::save()方法时激发。Action Hook: Fires when the WP_Customize_Setting::save() method is called.目录锚点:#说明#参数#源码说明(Description)钩子名称的动态部分,$this->id_data...

日期:2020-08-15 15:47:24 浏览:775

customize_value_{$this->id_data[‘base’]}

apply_filters( "customize_value_{$this-&gt;id_data[‘base’]}", mixed $default )过滤器::过滤未作为主题模式或选项处理的自定义设置值。Filter Hook: Filter a Customize setting value not handled as a theme_mod or option.目录锚点:#说明#参数#源码说明(Description)钩子名称的动态部分,$this->id_date['base'],指的是设置...

日期:2020-08-15 15:47:24 浏览:866

get_comment_author_url

过滤钩子:过滤评论作者的URL。Filter Hook: Filters the comment author’s URL.目录锚点:#源码源码(Source)更新版本源码位置使用被使用 wp-includes/comment-template.php:32610...

日期:2020-08-10 23:06:14 浏览:903

network_admin_edit_{$_GET[‘action’]}

do_action( "network_admin_edit_{$_GET[‘action’]}" )操作挂钩:启动请求的处理程序操作。Action Hook: Fires the requested handler action.目录锚点:#说明#源码说明(Description)钩子名称的动态部分$u GET['action']引用请求的操作的名称。源码(Source)更新版本源码位置使用被使用3.1.0 wp-admin/network/edit.php:3600...

日期:2020-08-02 09:56:09 浏览:848

network_sites_updated_message_{$_GET[‘updated’]}

apply_filters( "network_sites_updated_message_{$_GET[‘updated’]}", string $msg )筛选器挂钩:在网络管理中筛选特定的非默认站点更新消息。Filter Hook: Filters a specific, non-default site-updated message in the Network admin.目录锚点:#说明#参数#源码说明(Description)钩子名称的动态部分$_GET['updated']引用了非默认的...

日期:2020-08-02 09:56:03 浏览:834

pre_wp_is_site_initialized

过滤器::过滤在访问数据库之前是否初始化站点的检查。Filter Hook: Filters the check for whether a site is initialized before the database is accessed.目录锚点:#源码源码(Source)更新版本源码位置使用被使用 wp-includes/ms-site.php:93910...

日期:2020-07-29 10:15:38 浏览:809

WordPress 的SEO 教学:如何在网站中加入关键字(Meta Keywords)与Meta 描述(Meta Description)?

你想在WordPress 中添加关键字和meta 描述吗?关键字和meta 描述使你能够提高网站的SEO。在本文中,我们将向你展示如何在WordPress 中正确添加关键字和meta 描述。为什么要在WordPress 中添加关键字和Meta 描述?关键字和说明让搜寻引擎更了解您的帖子和页面的内容。关键词是人们寻找您发布的内容时,可能会搜索的重要词语或片语。而Meta Description则是对你的页面和文章的简要描述。如果你想要了解更多关于中继标签的资讯,可以参考Google的说明。Meta 关键字和描...

日期:2020-10-03 21:18:25 浏览:1620

谷歌的SEO是什么

SEO (Search Engine Optimization)中文是搜寻引擎最佳化,意思近于「关键字自然排序」、「网站排名优化」。简言之,SEO是以搜索引擎(如Google、Bing)为曝光媒体的行销手法。例如搜寻「wordpress教学」,会看到本站的「WordPress教学:12个课程…」排行Google第一:关键字:wordpress教学、wordpress课程…若搜寻「网站架设」,则会看到另一个网页排名第1:关键字:网站架设、架站…以上两个网页,每月从搜寻引擎导入自然流量,达2万4千:每月「有机搜...

日期:2020-10-30 17:23:57 浏览:1263