背景
在移動應用的開發過程中，繪制基本的二維圖形或動畫是必不可少的。然而，考慮到Android和iOS均有一套各自的API方案，因此采用一種更普遍接受的技術方案，更有利于代碼的雙平臺兼容。
art是一個旨在多瀏覽器兼容的Node style CommonJS模塊。在它的基礎上，Facebook又開發了React-art ，封裝art，使之可以被react.js所使用，即實現了前端的svg庫。然而，考慮到react.js的JSX語法，已經支持將 等等svg標簽直接插入到dom中（當然此時使用的就不是react-art庫了）此外還有HTML canvas的存在，因此，在前端上，react-art并非不可替代。
然而，在移動端，考慮到跨平臺的需求，加之web端的技術積累，react-art成為了現成的繪制圖形的解決方案。react-native分別在0.10.0和0.18.0上添加了ios和android平臺上對react-art的支持。
示例代碼
React.js和React-Native的區別，只在于下文所述的ART獲取上，然后該例子就可以同時應用在Web端和移動端上了。react-art自帶的官方例子：Vector-Widget
Vector-Widget額外實現了旋轉，以及鼠標點擊事件的旋轉加速響應。Web端可以看到點擊加速，但是在移動端無效，原因是React Native并未對Group中onMouseDown和onMouseUp屬性作處理。本文著重于靜態svg的實現，暫時無視動畫部分效果即可。
ART
在react native中ART是個非常重要的庫，它讓非常酷炫的繪圖及動畫變成了可能。需要注意的是，在React Native引入ART過程中，Android默認就包含ART庫，IOS需要單獨添加依賴庫。
ios添加依賴庫
1、使用xcode中打開React-native中的iOS項目，選中‘Libraries'目錄 ——> 右鍵選擇‘Add Files to 項目名稱' ——> ‘node_modules/react-native/Libraries/ART/ART.xcodeproj' 添加；
2、選中項目根目錄 ——> 點擊'Build Phases‘ ——> 點擊‘Link Binary With Libraries' ——> 點擊左下方‘+' ——> 選中‘libART.a'添加。
基礎組件
ART暴露的組件共有7個，本文介紹常用的四個組件：Surface、Group、Shape、Text。
屬性
Surface
Shape
Text
Path
代碼示例
繪制直線
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); //將起始點移動到(1,1) 默認(0,0)
path.lineTo(300,1); //連線到目標點(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>
)
}
}
繪制虛線
了解strokeDash的參數，
[10,5] : 表示繪10像素實線在繪5像素空白，如此循環
[10,5,20,5] : 表示繪10像素實線在繪制5像素空白在繪20像素實線及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>
)
}
}
繪制矩形
首先通過lineTo繪制三條邊，在使用close鏈接第四條邊。fill做顏色填充.
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="#892265" strokeWidth={1} />
</Surface>
</View>
)
}
}
繪圓
了解arc(x,y,radius)的使用, 終點坐標距離起點坐標的相對距離。
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>
)
}
}
繪制文字
了解funt屬性的使用，規則是“粗細 字號 字體”
注意： 字體應該是支持path屬性的，應該是實現bug并沒有不生效。 Android通過修改源碼是可以解決的，IOS沒看源碼。
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',
},
});
繪制扇形
在這里需要使用arc做路徑繪制。
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} />;
}
}
示例代碼：
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>
)
}
}
綜合示例
相關代碼：
/**
* Sample React Native App
* https://github.com/facebook/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對其他組件創建對話
//創建一個灰色的新型圖片
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={89}
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: 89, 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,
}
});
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