<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<meta name="Generator" content="EditPlus®">
<meta name="Author" content="">
<meta name="Keywords" content="">
<meta name="Description" content="">
<title>Document</title>
<script>
var startX, startY;
var isdown=0
function mouseUp(e,d)
{
isdown=0;
var c=document.getElementById("myCanvas");
height=c.style.height
width=c.style.width
var ctx=c.getContext("2d");
ctx.clearRect(0,0,350,350);
}
function mouseDown(e,d)
{
down_id=e.id;
startX = d.pageX;
startY = d.pageY;
isdown=1;
console.log(startX+",,,,"+startY)
}
function mousemove(e){
if(isdown){
//console.log(e.pageX+","+e.pageY)
// 更新 box 尺寸
//ab.style.width = e.pageX - startX + 'px';
//ab.style.height = e.pageY - startY + 'px';
//获取页面中的canvas画布容器，通常为一个div
var c=document.getElementById("myCanvas");
height=c.style.height
width=c.style.width
var ctx=c.getContext("2d");
ctx.lineWidth=1;
ctx.clearRect(0,0,350,350);
ctx.beginPath();
ctx.moveTo(startX,startY);
ctx.lineTo(e.pageX,startY);//shang heng
ctx.lineTo(e.pageX,e.pageY);//you
ctx.lineTo(startX,e.pageY);//zuo
ctx.closePath();
ctx.stroke();
}
}
</script>
</head>
<body onmouseup="mouseUp(this,event)" onmousemove="mousemove(event)" onmousedown='mouseDown(this,event)'>
<canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;">
您的浏览器不支持 HTML5 canvas 标签。</canvas>
</body>
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