（分享）一个图片添加水印的小demo的页面，可自定义样式

有时候想给某张图片添加一个自己的水印，但是又懒的下载相应软件，用js canvas制作一个静态页面，对于单张图片添加自定义文字水印，大小间距，角度可调。
页面如下：
在这里插入图片描述
选择图片，设置相应参数，点击添加水印：

效果：

完整程序如下：

<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>添加水印</title><link rel="shortcut icon" href="https://img1.imgtp.com/2024/01/09/BKw2wjPL.png" type="image/x-icon"><style>body {background-color: #c8adc4;}.ml-5 {margin-left: 15px;}.container {display: flex;justify-content: space-between;/* 使两个 div 平均分布在容器中 */}.box {width: 49.5%;/* 或根据需要设置 *//* 其他样式 */}#canvas {border: 2px solid rgb(210, 208, 208);width: 95%;height: auto;overflow: hidden;}#p {margin-top: 20px;width: 95%;height: auto;}#canvas img {width: 100%;height: 100%;object-fit: cover;}#imageUpload {height: auto;width: auto;font-size: 16px;}</style>
</head><body><div class="container"><div class="box"><div style="border: 2px solid #c9c9c9cc; padding: 10px;"><div><input type="file" id="imageUpload" style="color: rgb(249, 137, 109); margin-left: 40%;"></div><div style="margin-left: 10%;margin-top: 30px;"><span>大小：</span><input type="text" placeholder="修改水印大小" style="height: 24px;width: 100px;"value="100" id="ipt1"><span class="ml-5">透明度：</span><input type="text" placeholder="范围1~10"style="height: 24px;width: 100px;" value="5" id="ipt2"><span class="ml-5">间距：</span><input type="text" placeholder="范围1-10"style="height: 24px;width: 100px;" value="5" id="ipt3"></div><div style="margin-top: 20px;margin-left: 10%;"><span class="ml-5">倾斜方向：</span><select id="s2"><option value="left">左倾斜</option><option value="right">右倾斜</option></select><span class="ml-5">倾斜角度：</span><input type="text" placeholder="修改倾斜大小" style="height: 20px;width: 30px;" value="30" id="ipt4"><spanstyle="margin-left: 5px; ;">度</span></div><div style="margin-left: 10%;margin-top: 40px;">文本：<input type="text" id="watermarkText" placeholder="请输入水印内容" style="height: 24px;"><button id="confirmButton"style="margin-left: 100px; width: 80px;height: 30px;background-color: rgb(127, 214, 255);color: white;font-size: 16px;border: none;border-radius: 5px;">添加水印</button><button id="saveButton"style="width: 60px;height: 30px;background-color: rgb(28, 119, 161);color: white;font-size: 16px;border: none;border-radius: 5px;">下载</button><button id="reflash" onclick="flush()"style="width: 80px;height: 30px;background-color: rgb(248, 126, 81);color: white;font-size: 16px;border: none;border-radius: 5px;">重置页面</button></div></div><span style="color: rgb(255, 255, 255); font-weight: bold;font-size: 20px;">原图：</span><img id="p"></img></div><div class="box"><span style="color: rgb(255, 255, 255); font-weight: bold;font-size: 20px;">预览框：</span><canvas id="canvas"></canvas></div></div><script>//回显document.getElementById('imageUpload').addEventListener('change', function (e) {var reader = new FileReader();reader.onload = function (e) {document.getElementById('p').src = e.target.result;document.getElementById('p').style.display = 'block';}reader.readAsDataURL(e.target.files[0]);})//添加水印document.getElementById('confirmButton').addEventListener('click', function () {var image = document.getElementById('imageUpload').files[0]; //图片对象var watermarkText = document.getElementById('watermarkText').value; //水印对象var canvas = document.getElementById('canvas');  //canvasvar ctx = canvas.getContext('2d');var img = new Image(); //img对象var fontsize = document.getElementById('ipt1').value; //初始大小var transparency = document.getElementById('ipt2').value / 10; //透明度var jianju = document.getElementById('ipt3').value; //间距//单行多行//倾斜方式var tilt = document.getElementById('s2').value;var angle = document.getElementById('ipt4').value;img.onload = function () {canvas.width = img.width;canvas.height = img.height;ctx.drawImage(img, 0, 0, img.width, img.height);ctx.font = fontsize + 'px Arial'; //大小 字体ctx.fillStyle = `rgba(170, 171, 172, ${transparency})`;if (tilt === 'left') painWatermarket_left(watermarkText, canvas, jianju, ctx, angle);if (tilt === 'right') painWatermarket_right(watermarkText, canvas, jianju, ctx, angle);};img.src = URL.createObjectURL(image);});// 单行左倾斜params: watermarkText canvas jianju\ function painWatermarket_left(watermarkText, canvas, jianju, ctx, angle, lineNumber) {var txtLen = Math.ceil(ctx.measureText(watermarkText).width / 2);for (var i = 150 - txtLen, j = 150 - txtLen;i < canvas.width, j < canvas.height;i += canvas.width / jianju, j += canvas.height / jianju) {ctx.save();ctx.translate(i, j);ctx.rotate(angle * Math.PI / 180);ctx.fillText(watermarkText, 0, 0);ctx.restore();}}// 单行右倾斜params: watermarkText canvas jianjufunction painWatermarket_right(watermarkText, canvas, jianju, ctx, angle) {angle = -1 * angle;var txtLen = Math.ceil(ctx.measureText(watermarkText).width / 2); //文本宽度for (var i = 150 - txtLen, j = canvas.height; i < canvas.width, j > 150 - txtLen; i += canvas.width / jianju, j -= canvas.height / jianju) {ctx.save();ctx.translate(i, j);ctx.rotate(angle * Math.PI / 180);ctx.fillText(watermarkText, 0, 0);ctx.restore();}}//保存document.getElementById('saveButton').addEventListener('click', function () {var canvas = document.getElementById('canvas');var dataUrl = canvas.toDataURL('image/png');var blob = dataURItoBlob(dataUrl);var link = document.createElement('a');link.href = window.URL.createObjectURL(blob);link.download = 'demo.png';link.click();});function dataURItoBlob(dataURI) {var byteString;if (dataURI.split(',')[0].indexOf('base64') >= 0)byteString = atob(dataURI.split(',')[1]);elsebyteString = unescape(dataURI.split(',')[1]);var mimeString = dataURI.split(',')[0].split(':')[1].split(';')[0];var ab = new ArrayBuffer(byteString.length);var ia = new Uint8Array(ab);for (var i = 0; i < byteString.length; i++) {ia[i] = byteString.charCodeAt(i);}return new Blob([ab], { type: mimeString });}//重置function flush() {location.reload();}</script>
</body></html>