uniapp：手写签名，多张图合成一张图

要实现的内容：手写签名，协议内容。点击提交后：生成1张图片，有协议内容和签署日期和签署人。
实现的效果图如下：

1、签名页面

<template><view class="index"><u-navbar title="电子协议" :is-back="false" :border-bottom="false" title-color="#333" :background="{background:''}"><view class="page_navbar_warp"><image src="../../static/icon/0.png" mode="" class="page_navbar_commonImg" @click="$go(1,1)"></image></view></u-navbar><image src="https://www.*****/xieyi.png" mode="" class="banner"></image><view class="signBox"><view class="title">签名区</view><view style="width: 700rpx;height: 450rpx;"><l-signature disableScroll backgroundColor="rgba(255, 249, 238, .0)" ref="signatureRef" penColor="#333" :penSize="5" :openSmooth="true" ></l-signature></view></view><view class="footer"><view class="btn1 t-c" @click="onClick('undo')">撤消</view><u-button class="btn2 t-c" @click="onClick('save')" :loading="loading">提交</u-button></view></view>
</template><script>export default {data() {return {loading:false,}},methods:{onClick(type) {if(type == 'openSmooth') {this.openSmooth = !this.openSmoothreturn}if (type == 'save') {this.$refs.signatureRef.canvasToTempFilePath({success: (res) => {// 是否为空画板 无签名// 生成图片的临时路径// H5 生成的是base64let url = res.tempFilePath;console.log(res);if(res.isEmpty){this.$toast('请签名')}else{this.loading = true;this.$uploadImage('common/upload', url).then(res => {this.loading = false;if(res.code == 1){this.$go(2,'/pages/mine/canvas?signImg='+res.data.fullurl)}})}}})return}if (this.$refs.signatureRef) this.$refs.signatureRef[type]()}}}
</script><style scoped lang="scss">.index{min-height: 100vh;position: relative;.banner{display: block;width: 585rpx;height: 416rpx;margin: auto;}.signBox{border: 1rpx dashed #BF9350;width: 700rpx;height: 500rpx;margin: 32rpx auto;.title{padding-top: 32rpx;font-size: 40rpx;color: #BF9350;padding-left: 32rpx;}}.footer{position: fixed;left: 0;bottom: 0;width: 750rpx;height: 98rpx;background: #fff;box-shadow: 0rpx 3rpx 6rpx 1rpx rgba(0,0,0,0.32);padding: 0 50rpx;display: flex;align-items: center;justify-content: space-between;.btn1{width: 300rpx;height: 81rpx;border-radius: 41rpx 41rpx 41rpx 41rpx;border: 1rpx solid #BF9350;font-size: 32rpx;color: #BF9350;}.btn2{width: 300rpx;height: 81rpx;background: #BF9350;border-radius: 41rpx 41rpx 41rpx 41rpx;font-size: 32rpx;color: #fff;}}}
</style>

2、canvas页面，用来合成1张图

<template><view class="demo"><u-navbar title="电子协议" :is-back="false" :border-bottom="false" title-color="#333" :background="{background:'#FFFAF3'}"><view class="page_navbar_warp"><image src="../../static/icon/0.png" mode="" class="page_navbar_commonImg" @click="$go(1,1)"></image></view></u-navbar><canvas :style="{ width: canvasW + 'px', height: canvasH + 'px' }" canvas-id="myCanvas" id="myCanvas"></canvas><view class="footer"><view class="btn1 t-c" @click="$go(1,1)">取消</view><u-button class="btn2 t-c" @click="submit" :loading="loading" shape="circle" :ripple="true">提交</u-button></view></view>
</template>
<script>export default {components: {},data() {return {loading:false,canvasW:0, // 画布宽canvasH:0, // 画布高SystemInfo:{}, // 设备信息goodsImg: {}, // 协议图片signImg:{}, // 签名图片signW:120, // 签名图片大小bgImg:{},year:'',mon:'',date:'',tempFilePath:'',}},async onLoad(option) {var start = new Date();this.year = start.getFullYear();this.mon = start.getMonth() + 1;this.date = start.getDate();// 获取设备信息，主要获取宽度，赋值给canvasW 也就是宽度：100%this.SystemInfo = await this.getSystemInfo();// 获取协议图片，签名二维码图片信息，APP端会返回图片的本地路径（H5端只能返回原路径）this.bgImg = await this.getImageInfo('https://www.*******/xieyi.png');this.goodsImg = await this.getImageInfo('https://www.*******/bg.png');this.signImg = await this.getImageInfo(option.signImg);this.canvasW = this.SystemInfo.windowWidth; // 画布宽度// #ifdef APP-PLUSthis.canvasH = this.SystemInfo.windowHeight-94-uni.getSystemInfoSync().statusBarHeight;  // 画布高度 = 页面高度-(导航栏固定44px+footer的50px+APP内手机双跳栏的高度)// #endif// #ifdef H5this.canvasH = this.SystemInfo.windowHeight-94; // #endif// 如果主图，二维码图片，设备信息都获取成功，开始绘制海报，这里需要用setTimeout延时绘制，否则可能会出现图片不显示。if(this.goodsImg.errMsg == 'getImageInfo:ok' && this.signImg.errMsg == 'getImageInfo:ok' && this.SystemInfo.errMsg == 'getSystemInfo:ok'){uni.showToast({icon:'loading',mask:true,duration:10000,title: '加载中,请稍后',});setTimeout(()=>{var ctx = uni.createCanvasContext('myCanvas', this);// 填充背景ctx.drawImage(this.bgImg.path, 0, 0, this.canvasW, this.canvasH) // drawImage(图片路径,x,y,绘制图像的宽度，绘制图像的高度)// 绘制协议主图ctx.drawImage(this.goodsImg.path, 50, 60, this.canvasW-100, this.canvasW-180) // drawImage(图片路径,x,y,绘制图像的宽度，绘制图像的高度)// 签署日期ctx.setFontSize(16)ctx.setFillStyle('#333')ctx.fillText(`签署日期：${this.year}年${this.mon}月${this.date}日`, 50, this.canvasH -this.signW-80);// 签署人ctx.setFontSize(14)ctx.setFillStyle('#333')ctx.fillText('签署人：', 50, this.canvasH -this.signW-40);// 签署人ctx.drawImage(this.signImg.path, 90, this.canvasH-this.signW-80, this.signW, this.signW) // drawImage(图片路径,x,y,绘制图像的宽度，绘制图像的高度,二维码的宽,高)ctx.draw(true,(ret)=>{ // draw方法 把以上内容画到 canvas 中。console.log(ret) uni.showToast({icon:'success',mask:true,title: '绘制完成',});uni.canvasToTempFilePath({ // 保存canvas为图片canvasId: 'myCanvas',quality: 1,complete: (res)=> {console.log(res)// 在H5平台下，tempFilePath 为 base64, // 图片提示跨域 H5保存base64失败，APP端正常输出临时路径if(res.tempFilePath){this.tempFilePath = res.tempFilePath;}},})});},1500)}else{console.log('err')}},methods: {submit(){this.loading = true;console.log('需要提交给后台的图片'，this.tempFilePath)},// 获取图片信息getImageInfo(image) {return new Promise((req, rej) => {uni.getImageInfo({src: image,success: function(res) {req(res)},});})},// 获取设备信息getSystemInfo(){return new Promise((req, rej) => {uni.getSystemInfo({success: function (res) {req(res)}});})},},}
</script><style scoped lang="scss">.footer{position: fixed;left: 0;bottom: 0;width: 750rpx;height: 50px;box-shadow: 0rpx 3rpx 6rpx 1rpx rgba(0,0,0,0.32);padding: 0 50rpx;display: flex;align-items: center;justify-content: space-between;background: #fff;.btn1{width: 300rpx;height: 40px;border-radius: 41rpx 41rpx 41rpx 41rpx;border: 1rpx solid #BF9350;font-size: 32rpx;color: #BF9350;}.btn2{width: 300rpx;height: 40px;background: #BF9350;border-radius: 41rpx 41rpx 41rpx 41rpx;font-size: 32rpx;color: #fff;}}
</style>

备注：
1、协议页面内用的l-signature来自于uniapp插件市场
2、canvas页面灵感来自于之前写过的一篇绘制海报文章
3、页面中用到的 xieyi.png（协议内容）、bg.png（底图)、以及签名后的option.signImg（签名图），都需要后台设置允许跨域。否则H5就会报错画布污染无法生成base64。

这个问题在APP内不存在，只有H5会出现。