1、uniapp加水印

1.1、创建画布容器

<canvas class="watermark-canvas" id="watermark-canvas" canvas-id="watermark-canvas":style="{ width: canvasWidth, height: canvasHeight }" />

1.2、获取水印内容

async getLocation() {const zero = (item) => item < 10 ? "0" + item : itemconst time = new Date();const yy = time.getFullYear();const mm = time.getMonth() + 1;const dd = time.getDate();const hh = time.getHours();const MM = time.getMinutes();const ww = time.getDay()const hm = zero(hh) + ':' + zero(MM)const ymd = yy + '-' + zero(mm) + '-' + zero(dd)const {name: location} = await this.$store.dispatch('location/juGetLocation')return {hm,ymd,address: location}},

1.3、添加水印上传图片

async chooseImage(e) {// #ifdef APP-PLUSlet status = await this.checkPermission()if (status !== 1) {return}// }// #endifuni.chooseImage({sourceType: sourceType[this.sourceTypeIndex],sizeType: ['compressed'],count: this.limit,success: async (res) => {let filePath = res.tempFilePaths[0]const watermark = await this.getLocation()
//压缩图片设置宽度，不然画不全uni.compressImage({src: filePath,quality: 80,success: async comres => {//绘制图片加水印let img = await this.fillTextToImg(comres.tempFilePath, watermark)uni.showLoading({title: '上传中...',mask: true})const arr = [img]// 上传图片const key = await this.$store.dispatch('upload/uploadFileList', arr)this.$emit('handleChangeKeys', {src: key,create_time: watermark.hm,sign_date: watermark.ymd,sign_local: watermark.address})uni.hideLoading()}})},fail: (err) => {}})},sleep(millisecond) {return new Promise((resolve) => {setTimeout(resolve, millisecond)})},fillTextToImg(file, watermark) {return new Promise((resolve, reject) => {uni.getImageInfo({src: file,success: async res => {
//设置画布大小，然后再画，不然会只画一部分this.canvasWidth = `${res.width}px`this.canvasHeight = `${res.height}px`await this.sleep(200)const ctx = uni.createCanvasContext('watermark-canvas', this)ctx.clearRect(0, 0, res.width, res.height)ctx.beginPath()ctx.drawImage(res.path, 0, 0, res.width, res.height)// 水印 字体大小，颜色，内容，位置ctx.beginPath()ctx.setFillStyle('#ffffff')const fontSize = res.width / 10ctx.setFontSize(fontSize)ctx.fillText(watermark.hm, res.width / 2 - res.width / 8, res.height / 2 - 50)ctx.setFontSize(res.width / 15)ctx.fillText(watermark.ymd, res.width / 2 - res.width / 6, res.height / 2 + 100)ctx.setFontSize(res.width / 17)ctx.fillText(watermark.address, res.width / 5 - 15, res.height / 1.5 + 50)// 开始绘制 (canvas -> 临时文件路径)ctx.draw(false, async () => {await this.sleep(500) // 某些平台 canvas 渲染慢，需要等待uni.canvasToTempFilePath({canvasId: 'watermark-canvas',destWidth: res.width,destHeight: res.height,fileType: 'jpg',quality: 0.8,success: (fileRes) => {resolve(fileRes.tempFilePath)},fail: (err) => {uni.showToast({title: err.errMsg,icon: 'none'})reject()},},this,)})},fail: (err) => {console.log('[Error getImageInfo]', err)uni.showToast({title: err.errMsg,icon: 'none'})reject()},})});},

1.4、设置画布位置，不让其显示

.watermark-canvas {transform: scale(1);transform-origin: 0 0;position: absolute;top: -999px;left: -999px;}

2、web端加水印（Image，FileReaderweb端才能使用）

// 获取本地图片的base64编码
// 使用在线图片链接的时候需要注意给图片设置crossOrigin属性
function fileToBase64Async(file) {return new Promise((resolve, reject) => {let reader = new FileReader();reader.readAsDataURL(file);reader.onload = (e) => {resolve(e.target.result);};});
}// fillText绘制的是默认的普通实线文本，strokeText绘制的是描边文本
function fillTextToImg(base64) {const img = new Image();img.src = base64;img.setAttribute("crossOrigin", "Anonymous");return new Promise((resolve, reject) => {img.onload = () => {// 生成一个 canvas 画布；const canvas = document.createElement("canvas");canvas.width = img.width;canvas.height = img.height;// 将现有需要添加水印的图片绘制到画布上；const ctx = canvas.getContext("2d");ctx.fillRect(0, 0, canvas.width, canvas.height);ctx.drawImage(img, 0, 0, canvas.width, canvas.height);const remFontSize = canvas.width / 35;ctx.font = "bolder " + remFontSize + "px Verdana";ctx.textAlign = "center";/**ctx.textAlign = "center|end|left|right|start";start：默认，文本在指定的位置开始。end：文本在指定的位置结束。center：文本的中心在指定的位置。left：文本左对齐。right：文本右对齐。**/ctx.strokeStyle = "#fff";const name = "@AAAAAAAAAAAAA";const spaceH = remFontSize * 0.3;ctx.fillText(name,canvas.width / 2,canvas.height - remFontSize - spaceH);resolve(canvas.toDataURL("image/jpeg"));};});
}