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<!doctype html>
<html lang="zh-cn">
<head>
<meta charset="utf-8">
<title>html5 canvas</title>
<meta name="apple-touch-fullscreen" content="yes" />
<meta name="apple-mobile-web-app-capable" content="yes" />
<meta name="apple-mobile-web-app-status-bar-style" content="black" />
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no">
</head>
<body>
<canvas></canvas>
<script>
(function(bodyStyle) {
bodyStyle.mozUserSelect = 'none';
bodyStyle.webkitUserSelect = 'none';
var img = new Image();
var canvas = document.querySelector('canvas');
canvas.style.backgroundColor='transparent';
canvas.style.position = 'absolute';
img.addEventListener('load', function(e) {
var ctx;
var w = img.width,
h = img.height;
var offsetX = canvas.offsetLeft,
offsetY = canvas.offsetTop;
var mousedown = false;
function layer(ctx) {
var img=document.getElementById("lamp");
var pat=ctx.createPattern(img,"repeat");
ctx.fillStyle = pat;
ctx.fillRect(0, 0, w, h);
}
function eventDown(e){
e.preventDefault();
mousedown=true;
}
function eventUp(e){
e.preventDefault();
mousedown = false;
alert('0');
var data = ctx.getImageData(0,0,w,h).data;
alert('1');
for(var i=0,j=0;i<data.length;i+=4){
if(data[i] && data[i+1] && data[i+2] && data[i+3]){
j++;
}
}
//当图层被擦除剩余80%时触发
if(j<=w*h*0.8){
ctx.clearRect(0,0,w,h);
}
}
function eventMove(e){
e.preventDefault();
if(mousedown) {
if(e.changedTouches){
e=e.changedTouches[e.changedTouches.length-1];
}
var x = (e.clientX + document.body.scrollLeft || e.pageX) - offsetX || 0,
y = (e.clientY + document.body.scrollTop || e.pageY) - offsetY || 0;
with(ctx) {
beginPath()
arc(x, y, 20, 0, Math.PI * 2);
fill();
}
}
}
canvas.width=w;
canvas.height=h;
canvas.style.backgroundImage='url('+img.src+')';
ctx=canvas.getContext('2d');
ctx.fillStyle='transparent';
ctx.fillRect(0, 0, w, h);
layer(ctx);
ctx.globalCompositeOperation = 'destination-out';
canvas.addEventListener('touchstart', eventDown);
canvas.addEventListener('touchend', eventUp);
canvas.addEventListener('touchmove', eventMove);
canvas.addEventListener('mousedown', eventDown);
canvas.addEventListener('mouseup', eventUp);
canvas.addEventListener('mousemove', eventMove);
});
img.src = 'pet.jpg';
})(document.body.style);
</script>
<img id="lamp" src="pet2.jpg">
</body>
</html>
setInterval(function(){canvas.style.display='none'},25);
setInterval(function(){canvas.style.display='block'},25)