<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>canvas</title>
<style>
body{background: #000;}
#c1{background: #fff;}
</style>
<script>
window.onload = function(){
var oc = document.getElementById('c1');
var ogc = oc.getContext('2d');
oc.onmousedown = function(ev){
var ev = ev || window.event;
ogc.moveTo(ev.clientX-oc.offsetLeft,ev.clientY-oc.offsetTop);
document.onmousemove=function(ev){
var ev = ev || window.event;
ogc.lineTo(ev.clientX-oc.offsetLeft,ev.clientY-oc.offsetTop);
ogc.stroke();
}
document.onmouseup = function(){
document.onmousemove = null;
document.onmousedown = null;
}
}
ogc.stroke();
}
</script>
</head>
<body>
<canvas id="c1" width="400" height="400"></canvas>
</body>
</html>