版本1.0
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<style type="text/css">
.wrapper{
width: 300px;
height: 300px;
border: 1px solid black;
margin: 100px auto;
position: relative;
}
.wrapper canvas {
position: absolute;
left: 0;
right: 0;
}
.wrapper div{
position: absolute;
left: 0;
right: 0;
width: 100%;
height: 100%;
background-color: #f00;
}
.wrapper div img{
position: absolute;
left: 0;
right: 0;
width: 100%;
height: 100%;
}
</style>
</head>
<body>
<div class="wrapper">
<div class="item">
<img src="img/2test.jpg"/>
<canvas id="myCanvas" width="300" height="300"></canvas>
</div>
</div>
<script src="http://libs.baidu.com/jquery/2.0.0/jquery.min.js"></script>
<script>
var myCanvas = document.getElementById("myCanvas");
var ctx = myCanvas.getContext("2d");
ctx.fillRect(0,0,300,300);
ctx.globalCompositeOperation = "destination-out";
myCanvas.onmousedown = function (e) {
var parent = this.parentNode.parentNode;
document.onmousemove = function (e) {
var x = e.clientX - parent.offsetLeft;
var y = e.clientY - parent.offsetTop;
ctx.beginPath();
ctx.arc(x,y,20,0,2 * Math.PI,1);
ctx.fill();
}
document.onmouseup = function () {
document.onmousemove = null;
document.onmouseup = null;
}
}
