基本api就直接放源码了
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
body {
margin: 0;
padding: 0;
}
#canvas {
position: absolute;
left: 0;
}
</style>
</head>
<body onl oad="draw()">
<img src="./red.jpg" alt="">
<canvas id="canvas" width="680" height="453">
请更新版本!
</canvas>
<script>
function draw() {
var canvas = document.querySelector("#canvas");
if (canvas.getContext) {
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.fillStyle = "gray";
ctx.fillRect(0, 0, canvas.width, canvas.height)
ctx.globalCompositeOperation = 'destination-out';
ctx.lineWidth = 20;
ctx.lineCap = 'round';
canvas.onmousedown = function(e) {
var ev = e || window.event;
var x = ev.clientX;
var y = ev.clientY;
ctx.moveTo(x, y);
this.onmousemove = function(e) {
var ev = e || window.event;
var x = ev.clientX;
var y = ev.clientY;
ctx.lineTo(x, y);
ctx.stroke();
}
this.onmouseup = function(e) {
this.onmousemove = null;
}
}
}
}
</script>
</body>
</html>
希望对大家有帮助!!