共计 973 个字符，预计需要花费 3 分钟才能阅读完成。
一、效果图
二、上代码
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
#canvas{background: url(https://image-static.segmentfault.com/464/827/464827894-6363d955ba2a5_fix732);
background-size: 100%;
}
</style>
</head>
<body>
<canvas id="canvas" width="480" height="720">
你的浏览器不反对 canvas，请降级你的浏览器。</canvas>
<script>
const canvas = document.getElementById('canvas')
let ctx = canvas.getContext("2d")
ctx.beginPath();
ctx.fillStyle = '#9c9fb3';
ctx.fillRect(0, 0, canvas.width, canvas.height);
ctx.globalCompositeOperation = 'destination-out';
ctx.lineWidth = 60;
ctx.lineCap = 'round';
canvas.onmousedown = function(e) {
var event = e || window.event;
var x = event.clientX;
var y = event.clientY;
ctx.moveTo(x, y);
}
canvas.onmousemove = function(e) {
var event = e || window.event;
var x = event.clientX;
var y = event.clientY;
ctx.lineTo(x, y);
ctx.stroke();}
</script>
</body>
</html>三、重点 globalCompositeOperation 用法
正文完
