<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<meta name="viewport" content="width=device-width">
<meta name="description" content="">
<meta name="keywords" content="">
<style>
*{margin:0;padding:0;}
.out{
width: 800px;
margin: 50px auto;
position: relative;
}
.out p{
font-size: 24px;
color: red;
position: absolute;
top: 30px;
left: 50%;
transform: translateX(-50%);
}
.out button{
color: green;
font-style: 18px;
cursor: pointer;
position: absolute;
top: 20px;
right: 5%;
border: none;
background: none;
outline: none;
border: 1px solid green;
padding: 2px 4px;
border-radius: 2px;
}
#cvs1{
background: #eee;
cursor: pointer;
}
</style>
</head>
<body>
<div class="out">
<p>写写看...</p>
<button>清除</button>
<canvas id="cvs1" width="800" height="800"></canvas>
</div>
<script>
var cvs=document.getElementById('cvs1'),
ctx=cvs.getContext('2d'),
l=cvs.getBoundingClientRect().left,
t=cvs.getBoundingClientRect().top;
ctx.beginPath();
ctx.fillStyle="#eee";
ctx.fillRect(0,0,800,800);
ctx.closePath();
cvs.onmousedown=function(ev){
var ev=ev||window.event,
x=ev.clientX-l,
y=ev.clientY-t;
ctx.beginPath();
ctx.moveTo(x,y);
document.onmousemove=function(ev){
var ev=ev||window.event,
dx=ev.clientX-l;
dy=ev.clientY-t;
ctx.lineTo(dx,dy);
ctx.strokeStyle='red';
ctx.lineWidth=4;
ctx.stroke();
return false;
}
document.onmouseup=function(){
document.onmousedown=null;
document.onmousemove=null;
ctx.closePath();
}
return false;
}
document.getElementsByTagName('button')[0].onclick=function(){
ctx.clearRect(0,0,800,800);
}
</script>
</body>
</html>
