浅尝：iOS的CoreGraphics和Flutter的Canvas

iOS的CoreGraphic

基本就是创建一个自定义的UIView，然后重写drawRect方法，在此方法里使用UIGraphicsGetCurrentContext()来绘制目标图形和样式

#import <UIKit/UIKit.h>@interface MyGraphicView : UIView
@end@implementation MyGraphicView// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
// This method is called when a view is first displayed or when an event occurs that invalidates a visible part of the view.
- (void)drawRect:(CGRect)rect {CGRect rectangle = CGRectMake(0, 0, 320, 100);CGContextRef context = UIGraphicsGetCurrentContext();CGContextSetRGBFillColor(context, 1.0, 1.0, 1.0, 0.0);CGContextSetRGBStrokeColor(context, 0.0, 1.0, 0.0, 0.5);CGContextFillRect(context, rectangle);CGContextStrokeRect(context, rectangle);
}@end

Flutter的Canvas

这是main函数的主代码，在child节点实现一个自定义的画布

import 'package:flutter/material.dart';final Color darkBlue = Color.fromARGB(255, 18, 32, 47);void main() {runApp(MyApp());
}class MyApp extends StatelessWidget {@overrideWidget build(BuildContext context) {return MaterialApp(debugShowCheckedModeBanner: false,theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),home: Scaffold(// Outer white container with padding body: Container(padding: EdgeInsets.symmetric(horizontal: 40, vertical: 80),color: Colors.white,child: Container(child: CustomPaint(painter: FaceOutlinePainter()),),),),);}
}

自定义一个类继承自CustomPainter，然后重写paint()方法

class FaceOutlinePainter extends CustomPainter {@overridevoid paint(Canvas canvas, Size size) {// 先定义一个画笔paint实例对象final paint = Paint()..style = PaintingStyle.stroke..strokeWidth = 4.0..color = Colors.indigo;// 画左边的眼睛，是一个矩形的，并且有圆角20canvas.drawRRect(RRect.fromRectAndRadius(Rect.fromLTWH(20, 40, 100, 100), Radius.circular(20)),paint,);// 画右边的眼睛，是圆形的canvas.drawOval(Rect.fromLTWH(size.width - 120, 40, 100, 100),paint,);// 画嘴巴// 先初始化一个路径Pathfinal mouth = Path();// 然后从左移动到右边mouth.moveTo(size.width * 0.8, size.height * 0.6);// 然后画椭圆曲线mouth.arcToPoint(Offset(size.width * 0.2, size.height * 0.6),radius: Radius.circular(150),);mouth.arcToPoint(Offset(size.width * 0.8, size.height * 0.6),radius: Radius.circular(200),clockwise: false,);// 把嘴巴画的线路径添加到canvas上进行绘制canvas.drawPath(mouth, paint);}@overridebool shouldRepaint(FaceOutlinePainter oldDelegate) => false;
}

输出的图形大概如下所示