微信小程序canvas实现抽奖动画

本来想用setdata做抽奖动画的，但是存在合并更新以及性能问题，遂采用canvas的形式。

参考了一篇blog，然后加了些抽奖逻辑的改动

<!--components/names/names.wxml-->
<view class="component-names"><canvas type="2d" id="myCanvas" style="width: 200px;height: 200px;"></canvas>
</view>

import { getRandomInt } from "../../utils/util";// components/names/names.ts
Component({lifetimes: {attached() {this.createSelectorQuery().select("#myCanvas").fields({node: true,size: true}).exec(res => this.init(res));},},/*** 组件的属性列表*/properties: {names: {type: Array,value: ['小红', '大明', '阿花']}},/*** 组件的初始数据*/data: {},/*** 组件的方法列表*/methods: {init(res) {// console.log('init', res)const width = res[0].widthconst height = res[0].height// 设置画布宽高const canvas = res[0].nodeconst ctx = canvas.getContext('2d')canvas.width = widthcanvas.height = height/** 半径 */let rArr = [];/** 透明度 */let alpha = [];const renderLoop = () => {/** 最小半径 */const circleStartR = width / 2 - 40;/** 最大半径 */const circleEndR = width / 2 - 8;/** 动画时间 */let animationTime = 300;/** 每次增大的宽度 */let speed = (circleEndR - circleStartR) / animationTime;rArr = rArr.map(item => item + speed);alpha = alpha.map(item => item + 1 / animationTime);// 如果数组为空|| 最小圆半径-最小半径>圆间隔if (!rArr[0] || rArr[0] - circleStartR > 10) {rArr.unshift(circleStartR);alpha.unshift(0);}// 如果最大圆半径>=最大半径if (rArr[rArr.length - 1] >= circleEndR) {rArr.pop();}this.render(width, ctx, rArr, alpha)canvas.requestAnimationFrame(renderLoop)}canvas.requestAnimationFrame(renderLoop)},renderName(width, ctx) {const center = width / 2;ctx.clearRect(center - 50, center - 50, center, center)let name = this.properties.names[getRandomInt(0, this.properties.names.length - 1)];let w = ctx.measureText(name).width;ctx.fillText(name, center - w / 2, center + 10)ctx.font = '30px bold'},render(width, ctx, rArr, alpha) {ctx.clearRect(0, 0, width, width);const center = width / 2;this.renderName(width, ctx);function ball(r, a) {// 设置渐变let grd = ctx.createLinearGradient(0, 0, 100, 0);grd.addColorStop(0, 'rgba(132, 251, 251, ' + a + ')') //渐变颜色的添加grd.addColorStop(0.5, 'rgba(118, 133, 254, ' + a + ')');grd.addColorStop(1, 'rgba(2545, 4, 255, ' + a + ')');ctx.beginPath();// 画圆ctx.arc(center, center, r, 0, 2 * Math.PI);// 描边样式设置ctx.strokeStyle = grd;ctx.closePath();// 描边ctx.stroke();}for (let i = 0; i < rArr.length; i++) {let r = rArr[i];let a = alpha[i];ball(r, a);}},}
})

参考：微信小程序canvas制作动画_微信小程序 canvas动画-CSDN博客