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watermark-helper.html
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<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8">
<title>水印助手</title>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<style>
body {
margin: auto;
max-width: 60vh;
}
img {
border: 3px solid #2c3e50;
border-radius: 5px;
width: 100%;
box-sizing: border-box
}
canvas {
width: 100%;
height: 0;
}
label, a {
display: flex;
align-items: center;
margin-top: 8px;
}
</style>
</head>
<body>
<canvas></canvas>
<div>
<input id="upload-input" type="file" accept="image/*">
<label>
水印文字：
<input id="content" type="text" value="仅供XX实名认证使用">
</label>
<label>
水印颜色：
<input id="color" type="color" value="#ffffff">
</label>
<label>
不透明度：
<input id="alpha" type="range" min="10" max="100" value="50">
</label>
<label>
水印大小比：
<input id="size" type="range" min="3" max="10" value="5">
</label>
<label>
水印间隔比：
<input id="gap" type="range" min="20" max="300" value="150">
</label>
<label>
水印字体：
<input id="font" type="text" value="sans-serif">
</label>
<a href="javascript:alert('请先打开图片')" download>保存图片</a>
</div>
<script>
var img = null;
document.addEventListener('change', function (ev) {
if (ev.target.type === 'file') {
if (!ev.target.files.length) return;
var file = ev.target.files[0];
createBitmap(file, function (result) {
img = result;
repaint()
});
} else {
repaint()
}
});
function repaint() {
if (!img) return;
var ctx = document.getElementsByTagName('canvas')[0].getContext('2d');
ctx.canvas.width = img.width;
ctx.canvas.height = img.height;
var maxSize = Math.max(img.height, img.width);
ctx.canvas.style.height = (img.height / img.width) * 100 + '%';
ctx.restore();
ctx.drawImage(img, 0, 0);
ctx.fillStyle = document.getElementById('color').value;
ctx.globalAlpha = document.getElementById('alpha').value / 100;
var size = (document.getElementById('size').value * maxSize / 100);
ctx.font = size + 'px "'+document.getElementById('font').value+'"';
ctx.textBaseline = 'middle';
ctx.rotate(-45 * Math.PI / 180);
var gap = size * document.getElementById('gap').value / 100;
var content = document.getElementById('content').value;
if (!content.length) return;
var limit = Math.sqrt(2*(maxSize*maxSize));
var breaker = ctx.measureText(content).width;
for (var h = -maxSize, even = false; h <= limit; h += size + gap, even = !even){
for (var v = -maxSize-(even?breaker/2:0); v<=limit+(even?breaker/2:0); v += breaker + size){
ctx.fillText(content, v, h);
}
}
document.getElementsByTagName('a')[0].href = ctx.canvas.toDataURL()
}
function createBitmap(blob, callback) {
var img = document.createElement('img');
img.addEventListener('load', function () {
callback(this);
});
img.src = URL.createObjectURL(blob);
}
</script>
</body>
</html>