背景

在移动应用的开发过程中，绘制基本的二维图形或动画是必不可少的。然而，考虑到Android和iOS均有一套各自的API方案，因此采用一种更普遍接受的技术方案，更有利于代码的双平台兼容。

art是一个旨在多浏览器兼容的Node style CommonJS模块。在它的基础上，又开发了React-art ，封装art，使之可以被react.js所使用，即实现了前端的svg库。然而，考虑到react.js的JSX语法，已经支持将 等等svg标签直接插入到dom中（当然此时使用的就不是react-art库了）此外还有HTML canvas的存在，因此，在前端上，react-art并非不可替代。

然而，在移动端，考虑到跨平台的需求，加之web端的技术积累，react-art成为了现成的绘制图形的解决方案。react-native分别在0.10.0和0.18.0上添加了ios和android平台上对react-art的支持。

示例代码

React.js和React-Native的区别，只在于下文所述的ART获取上，然后该例子就可以同时应用在Web端和移动端上了。react-art自带的官方例子：Vector-Widget

Vector-Widget额外实现了旋转，以及鼠标点击事件的旋转加速响应。Web端可以看到点击加速，但是在移动端无效，原因是React Native并未对Group中onMouseDown和onMouseUp属性作处理。本文着重于静态svg的实现，暂时无视动画部分效果即可。

ART

在react native中ART是个非常重要的库，它让非常酷炫的绘图及动画变成了可能。需要注意的是，在React Native引入ART过程中，Android默认就包含ART库，IOS需要单独添加依赖库。

ios添加依赖库

1、使用xcode中打开React-native中的iOS项目，选中‘Libraries'目录 ——> 右键选择‘Add Files to 项目名称' ——> ‘node_modules/react-native/Libraries/ART/ART.xcodeproj' 添加；

2、选中项目根目录 ——> 点击'Build Phases‘ ——> 点击‘Link Binary With Libraries' ——> 点击左下方‘+' ——> 选中‘libART.a'添加。

基础组件

ART暴露的组件共有7个，本文介绍常用的四个组件：Surface、Group、Shape、Text。

属性

Surface

Shape

Text

Path

代码示例

绘制直线

import React from 'react'
import {
 View,
 ART
} from 'react-native'

export default class Line extends React.Component{

 render(){

 const path = ART.Path();
 path.moveTo(1,1); //将起始点移动到(1,1) 默认(0,0)
 path.lineTo(300,1); //连线到目标点(300,1)

 return(
 <View style={this.props.style}>
 <ART.Surface width={300} height={2}>
 <ART.Shape d={path} stroke="#000000" strokeWidth={1} />
 </ART.Surface>
 </View>
 )
 }
}

绘制虚线

了解strokeDash的参数，

[10,5] : 表示绘10像素实线在绘5像素空白，如此循环

[10,5,20,5] : 表示绘10像素实线在绘制5像素空白在绘20像素实线及5像素空白

import React from 'react'
import {
 View,
 ART
} from 'react-native'

const {Surface, Shape, Path} = ART;

export default class DashLine extends React.Component{

 render(){

 const path = Path()
 .moveTo(1,1)
 .lineTo(300,1);

 return(
 <View style={this.props.style}>
 <Surface width={300} height={2}>
 <Shape d={path} stroke="#000000" strokeWidth={2} strokeDash={[10,5]}/>
 </Surface>
 </View>
 )
 }
}

绘制矩形

首先通过lineTo绘制三条边，在使用close链接第四条边。fill做颜色填充.

import React from 'react'
import {
 View,
 ART
} from 'react-native'

const {Surface, Shape, Path} = ART;

export default class Rect extends React.Component{

 render(){

 const path = new Path()
 .moveTo(1,1)
 .lineTo(1,99)
 .lineTo(99,99)
 .lineTo(99,1)
 .close();

 return(
 <View style={this.props.style}>
 <Surface width={100} height={100}>
 <Shape d={path} stroke="#000000" fill="#2265" strokeWidth={1} />
 </Surface>
 </View>
 )
 }
}

绘圆

了解arc(x,y,radius)的使用, 终点坐标距离起点坐标的相对距离。

import React from 'react'
import {
 View,
 ART
} from 'react-native'

const {Surface, Shape, Path} = ART;

export default class Circle extends React.Component{

 render(){

 const path = new Path()
 .moveTo(50,1)
 .arc(0,99,25)
 .arc(0,-99,25)
 .close();


 return(
 <View style={this.props.style}>
 <Surface width={100} height={100}>
 <Shape d={path} stroke="#000000" strokeWidth={1}/>
 </Surface>
 </View>
 )
 }
}

绘制文字

了解funt属性的使用，规则是“粗细 字号 字体”

注意： 字体应该是支持path属性的，应该是实现bug并没有不生效。 Android通过修改源码是可以解决的，IOS没看源码。

import React, {Component} from 'react';
import {
 AppRegistry,
 StyleSheet,
 ART,
 View
} from 'react-native';

const {Surface, Text, Path} = ART;

export default class ArtTextView extends Component {

 render() {

 return (
 <View style={styles.container}>
 <Surface width={100} height={100}>
 <Text strokeWidth={1} stroke="#000" font="bold 35px Heiti SC" path={new Path().moveTo(40,40).lineTo(99,10)} >React</Text>
 </Surface>

 </View>

 );
 }
}

const styles = StyleSheet.create({
 container: {
 flex: 1,
 justifyContent: 'center',
 alignItems: 'center',
 backgroundColor: '#F5FCFF',
 },

});

绘制扇形

在这里需要使用arc做路径绘制。

Wedge.js

import React, { Component, PropTypes } from 'react';
import { ART } from 'react-native';
const { Shape, Path } = ART;

/**
 * Wedge is a React component for drawing circles, wedges and arcs. Like other
 * ReactART components, it must be used in a <Surface>.
 */
export default class Wedge extends Component<void, any, any> {

 static propTypes = {
 outerRadius: PropTypes.number.isRequired,
 startAngle: PropTypes.number.isRequired,
 endAngle: PropTypes.number.isRequired,
 originX: PropTypes.number.isRequired,
 originY: PropTypes.number.isRequired,
 innerRadius: PropTypes.number,
 };


 constructor(props : any) {
 super(props);
 (this:any).circleRadians = Math.PI * 2;
 (this:any).radiansPerDegree = Math.PI / 180;
 (this:any)._degreesToRadians = this._degreesToRadians.bind(this);
 }

 /**
 * _degreesToRadians(degrees)
 *
 * Helper function to convert degrees to radians
 *
 * @param {number} degrees
 * @return {number}
 */
 _degreesToRadians(degrees : number) : number {
 if (degrees !== 0 && degrees % 360 === 0) { // 360, 720, etc.
 return (this:any).circleRadians;
 }
 return degrees * (this:any).radiansPerDegree % (this:any).circleRadians;
 }

 /**
 * _createCirclePath(or, ir)
 *
 * Creates the ReactART Path for a complete circle.
 *
 * @param {number} or The outer radius of the circle
 * @param {number} ir The inner radius, greater than zero for a ring
 * @return {object}
 */
 _createCirclePath(or : number, ir : number) : Path {
 const path = new Path();

 path.move(0, or)
 .arc(or * 2, 0, or)
 .arc(-or * 2, 0, or);

 if (ir) {
 path.move(or - ir, 0)
 .counterArc(ir * 2, 0, ir)
 .counterArc(-ir * 2, 0, ir);
 }

 path.close();

 return path;
 }

 /**
 * _createArcPath(sa, ea, ca, or, ir)
 *
 * Creates the ReactART Path for an arc or wedge.
 *
 * @param {number} startAngle The starting degrees relative to 12 o'clock
 * @param {number} endAngle The ending degrees relative to 12 o'clock
 * @param {number} or The outer radius in pixels
 * @param {number} ir The inner radius in pixels, greater than zero for an arc
 * @return {object}
 */
 _createArcPath(originX : number, originY : number, startAngle : number, endAngle : number, or : number, ir : number) : Path {
 const path = new Path();

 // angles in radians
 const sa = this._degreesToRadians(startAngle);
 const ea = this._degreesToRadians(endAngle);

 // central arc angle in radians
 const ca = sa > ea ? (this:any).circleRadians - sa + ea : ea - sa;

 // cached sine and cosine values
 const ss = Math.sin(sa);
 const es = Math.sin(ea);
 const sc = Math.cos(sa);
 const ec = Math.cos(ea);

 // cached differences
 const ds = es - ss;
 const dc = ec - sc;
 const dr = ir - or;

 // if the angle is over pi radians (180 degrees)
 // we will need to let the drawing method know.
 const large = ca > Math.PI;

 // TODO (sema) Please improve theses comments to make the math
 // more understandable.
 //
 // Formula for a point on a circle at a specific angle with a center
 // at (0, 0):
 // x = radius * Math.sin(radians)
 // y = radius * Math.cos(radians)
 //
 // For our starting point, we offset the formula using the outer
 // radius because our origin is at (top, left).
 // In typical web layout fashion, we are drawing in quadrant IV
 // (a.k.a. Southeast) where x is positive and y is negative.
 //
 // The arguments for path.arc and path.counterArc used below are:
 // (endX, endY, radiusX, radiusY, largeAngle)

 path.move(or + or * ss, or - or * sc) // move to starting point
 .arc(or * ds, or * -dc, or, or, large) // outer arc
 .line(dr * es, dr * -ec); // width of arc or wedge

 if (ir) {
 path.counterArc(ir * -ds, ir * dc, ir, ir, large); // inner arc
 }

 return path;
 }

 render() : any {
 // angles are provided in degrees
 const startAngle = this.props.startAngle;
 const endAngle = this.props.endAngle;
 // if (startAngle - endAngle === 0) {
 // return null;
 // }

 // radii are provided in pixels
 const innerRadius = this.props.innerRadius || 0;
 const outerRadius = this.props.outerRadius;

 const { originX, originY } = this.props;

 // sorted radii
 const ir = Math.min(innerRadius, outerRadius);
 const or = Math.max(innerRadius, outerRadius);

 let path;
 if (endAngle >= startAngle + 360) {
 path = this._createCirclePath(or, ir);
 } else {
 path = this._createArcPath(originX, originY, startAngle, endAngle, or, ir);
 }

 return <Shape {...this.props} d={path} />;
 }
}

示例代码：

import React from 'react'
import {
 View,
 ART
} from 'react-native'

const {Surface} = ART;
import Wedge from './Wedge'

export default class Fan extends React.Component{

 render(){

 return(
 <View style={this.props.style}>
 <Surface width={100} height={100}>
 <Wedge
 outerRadius={50}
 startAngle={0}
 endAngle={60}
 originX={50}
 originY={50}
 fill="blue"/>

 </Surface>
 </View>
 )
 }
}

综合示例

相关代码：

/**
 * Sample React Native App
 * https://github.com//react-native
 * @flow
 */

import React, {
 Component
}from 'react';
import {
 ART as Art,
 StyleSheet,
 View,
 Dimensions,
 TouchableWithoutFeedback,
 Animated
} from 'react-native';

var HEART_SVG = "M130.4-0.8c25.4 0 46 20.6 46 46.1 0 13.1-5.5 24.9-14.2 33.3L88 153.6 12.5 77.3c-7.9-8.3-12.8-19.6-12.8-31.9 0-25.5 20.6-46.1 46-46.2 19.1 0 35.5 11.7 42.4 28.4C94.9 11 111.3-0.8 130.4-0.8"
var HEART_COLOR = 'rgb(226,38,77,1)';
var GRAY_HEART_COLOR = "rgb(204,204,204,1)";

var FILL_COLORS = [
 'rgba(221,70,136,1)',
 'rgba(212,106,191,1)',
 'rgba(204,142,245,1)',
 'rgba(204,142,245,1)',
 'rgba(204,142,245,1)',
 'rgba(0,0,0,0)'
];

var PARTICLE_COLORS = [
 'rgb(158, 202, 250)',
 'rgb(161, 235, 206)',
 'rgb(208, 148, 246)',
 'rgb(244, 141, 166)',
 'rgb(234, 171, 104)',
 'rgb(170, 163, 186)'
]

getXYParticle = (total, i, radius) => {
 var angle = ( (2 * Math.PI) / total ) * i;

 var x = Math.round((radius * 2) * Math.cos(angle - (Math.PI / 2)));
 var y = Math.round((radius * 2) * Math.sin(angle - (Math.PI / 2)));
 return {
 x: x,
 y: y,
 }
}

getRandomInt = (min, max) => {
 return Math.floor(Math.random() * (max - min)) + min;
}

shuffleArray = (array) => {
 for (var i = array.length - 1; i > 0; i--) {
 var j = Math.floor(Math.random() * (i + 1));
 var temp = array[i];
 array[i] = array[j];
 array[j] = temp;
 }
 return array;
}


var {
 Surface,
 Group,
 Shape,
 Path
} = Art;

//使用Animated.createAnimatedComponent对其他组件创建对话
//创建一个灰色的新型图片
var AnimatedShape = Animated.createAnimatedComponent(Shape);

var {
 width: deviceWidth,
 height: deviceHeight
} = Dimensions.get('window');

export default class ArtAnimView extends Component {
 constructor(props) {
 super(props);

 this.state = {
 animation: new Animated.Value(0)
 };
 }

 explode = () => {
 Animated.timing(this.state.animation, {
 duration: 1500,
 toValue: 28
 }).start(() => {
 this.state.animation.setValue(0);
 this.forceUpdate();
 });
 }

 getSmallExplosions = (radius, offset) => {
 return [0, 1, 2, 3, 4, 5, 6].map((v, i, t) => {

 var scaleOut = this.state.animation.interpolate({
 inputRange: [0, 5.99, 6, 13.99, 14, 21],
 outputRange: [0, 0, 1, 1, 1, 0],
 extrapolate: 'clamp'
 });

 var moveUp = this.state.animation.interpolate({
 inputRange: [0, 5.99, 14],
 outputRange: [0, 0, -15],
 extrapolate: 'clamp'
 });

 var moveDown = this.state.animation.interpolate({
 inputRange: [0, 5.99, 14],
 outputRange: [0, 0, 15],
 extrapolate: 'clamp'
 });

 var color_top_particle = this.state.animation.interpolate({
 inputRange: [6, 8, 10, 12, 17, 21],
 outputRange: shuffleArray(PARTICLE_COLORS)
 })

 var color_bottom_particle = this.state.animation.interpolate({
 inputRange: [6, 8, 10, 12, 17, 21],
 outputRange: shuffleArray(PARTICLE_COLORS)
 })

 var position = getXYParticle(7, i, radius)

 return (
 <Group
 x={position.x + offset.x }
 y={position.y + offset.y}
 rotation={getRandomInt(0, 40) * i}
 >
 <AnimatedCircle
 x={moveUp}
 y={moveUp}
 radius={15}
 scale={scaleOut}
 fill={color_top_particle}
 />
 <AnimatedCircle
 x={moveDown}
 y={moveDown}
 radius={8}
 scale={scaleOut}
 fill={color_bottom_particle}
 />
 </Group>
 )
 }, this)
 }

 render() {
 var heart_scale = this.state.animation.interpolate({
 inputRange: [0, .01, 6, 10, 12, 18, 28],
 outputRange: [1, 0, .1, 1, 1.2, 1, 1],
 extrapolate: 'clamp'
 });

 var heart_fill = this.state.animation.interpolate({
 inputRange: [0, 2],
 outputRange: [GRAY_HEART_COLOR, HEART_COLOR],
 extrapolate: 'clamp'
 })

 var heart_x = heart_scale.interpolate({
 inputRange: [0, 1],
 outputRange: [90, 0],
 })

 var heart_y = heart_scale.interpolate({
 inputRange: [0, 1],
 outputRange: [75, 0],
 })

 var circle_scale = this.state.animation.interpolate({
 inputRange: [0, 1, 4],
 outputRange: [0, .3, 1],
 extrapolate: 'clamp'
 });

 var circle_stroke_width = this.state.animation.interpolate({
 inputRange: [0, 5.99, 6, 7, 10],
 outputRange: [0, 0, 15, 8, 0],
 extrapolate: 'clamp'
 });

 var circle_fill_colors = this.state.animation.interpolate({
 inputRange: [1, 2, 3, 4, 4.99, 5],
 outputRange: FILL_COLORS,
 extrapolate: 'clamp'
 })

 var circle_opacity = this.state.animation.interpolate({
 inputRange: [1, 9.99, 10],
 outputRange: [1, 1, 0],
 extrapolate: 'clamp'
 })


 return (
 <View style={styles.container}>
 <TouchableWithoutFeedback onPress={this.explode} style={styles.container}>
 <View style={{transform: [{scale: .8}]}}>
 <Surface width={deviceWidth} height={deviceHeight}>
 <Group x={75} y={200}>
 <AnimatedShape
 d={HEART_SVG}
 x={heart_x}
 y={heart_y}
 scale={heart_scale}
 fill={heart_fill}
 />
 <AnimatedCircle
 x={}
 y={75}
 radius={150}
 scale={circle_scale}
 strokeWidth={circle_stroke_width}
 stroke={FILL_COLORS[2]}
 fill={circle_fill_colors}
 opacity={circle_opacity}
 />

 {this.getSmallExplosions(75, {x: , y: 75})}
 </Group>
 </Surface>
 </View>
 </TouchableWithoutFeedback>
 </View>
 );
 }
};

class AnimatedCircle extends Component {
 render() {
 var radius = this.props.radius;
 var path = Path().moveTo(0, -radius)
 .arc(0, radius * 2, radius)
 .arc(0, radius * -2, radius)
 .close();
 return React.createElement(AnimatedShape);
 }
}

var styles = StyleSheet.create({
 container: {
 flex: 1,
 }
});