canvas写的一个刮奖效果

<!DOCTYPE html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title></title>
<meta name="description" content="刮奖">
<meta name="viewport" content="width=device-width, initial-scale=1">

<style>
body{margin: 0;}
#price{width: 200px; height: 100px; font-size: 40px; color: #f60; line-height: 100px; text-align: center;}
#canvas{position: absolute; top: 0; left: 0;}
</style>
</head>

<body>

<div id="price">DFAFAFAFFAF</div>
<canvas id="canvas" width="200" height="100"></canvas>
<script type="text/javascript">
var can = document.getElementById('canvas');
var touchRadius = 5;
ctx = can.getContext('2d');
ctx.fillStyle = '#ccc';
ctx.fillRect(0,0,200,100);
var img = new Image();
img.src = '1.jpg'
img.onload = function(){
ctx.drawImage(img,0,0)
}
var fillCircle = function(x,y,radius,fillColor){
this.fillStyle = fillColor || '#eee';
this.beginPath();
this.moveTo(x,y);
this.arc(x,y,radius,0,Math.PI *2,false);
this.fill();
}
var getBaifenbi = function(ctx,width,height){

var imgData = ctx.getImageData(0,0,width,height);
pix = imgData.data;
var str = [];
for(var i = 0;i<pix.length;i+=4){
var a = pix[i+3];
if(a===0){
str.push(i);
}

}
return (str.length/(pix.length/4)*100).toFixed(2);
}
var device = /android|webos|iphone|ipad|ipod|blackberry|iemobile|opera mini/i.test(navigator.userAgent.toLowerCase());
var clickName = device ? 'touchstart' : 'mousedown';
var moveName = device ? 'touchmove' : 'mousemove';
if(!device){
var isMouseDown = false;
document.addEventListener('mouseup',function(e){
isMouseDown = false;
},false)
}else{
document.addEventListener('touchmove',function(e){
if(isMouseDown){
e.preventDefault();
}
},false)
document.addEventListener('touchend',function(e){
isMouseDown = false;
},false)
}
can.addEventListener(clickName,function(e){
isMouseDown = true;
var x = (device ? e.touches[0].pageX : e.clientX);
var y = (device ? e.touches[0].pageY : e.clientY);
ctx.globalCompositeOperation = 'destination-out';
fillCircle.call(ctx,x,y,touchRadius);
},false);
can.addEventListener(moveName,function(e){
if(!device&& !isMouseDown){
return false;
}
var x = (device ? e.touches[0].pageX : e.clientX);
var y = (device ? e.touches[0].pageY : e.clientY);
ctx.globalCompositeOperation = 'destination-out';
fillCircle.call(ctx,x,y,touchRadius);
var m = getBaifenbi(ctx, 200, 100);
console.log(m)
if(m>50){alert('gggg')}
},false)
</script>
</body>

</html>

posted @ 2016-11-28 20:39  <张磊>  阅读(187)  评论(0)    收藏  举报