我要评论本文实例为大家分享了canvas实现橡皮擦效果的具体代码，供大家参考，具体内容如下
html部分
<!doctype html>
<html>
<head>
<meta http-equiv="content-type" content="text/html" charset="utf-8" />
<meta name="viewport" content="initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no" />
<title>my canvas 0.1</title>
<style type="text/css">
html,body,div,img{
margin:0;
padding:0;
}
a,a:hover{
text-decoration:none;
}
.background{
width:100%;
position:fixed;
top:0;
left:0;
}
</style>
</head>
<body>
<img src="images/background.png" class="background resizecontainer"/>
<div id="j_cover" class="resizecontainer"></div>
<script type="text/javascript" src="js/zepto.js"></script>
<script type="text/javascript" src="js/lottery.js"></script>
<script type="text/javascript">
var canvas = {
init : function(){
var self = this;
var node = document.getelementbyid('j_cover'),
canvas_url = 'images/cover.png',
type = 'image';
var lottery = new lottery(node, canvas_url, type, window_w, window_h, self.callback);
lottery.init();
},
callback : function(){
$('#j_cover').hide();
}
}
var window_h, window_w;
$(document).ready(function(){
window_w = $(window).width();
window_h = $(window).height();
$('.resizecontainer').width(window_w).height(window_h);
canvas.init();
});
</script>
</body>
</html>
lottery.js
function lottery(node, cover, covertype, width, height, drawpercentcallback) {
//node：canvas的id，cover：上面一层的图片地址，covertype：'image'or'color'，width：canvas宽, height：canvas高, drawpercentcallback：回调函数
//canvas
this.connode = node;
this.background = null;
this.backctx = null;
this.mask = null;
this.maskctx = null;
this.lottery = null;
this.lotterytype = 'image';
this.cover = cover || "#000";
this.covertype = covertype;
this.pixlesdata = null;
this.width = width;
this.height = height;
this.lastposition = null;
this.drawpercentcallback = drawpercentcallback;
this.vail = false;
}
lottery.prototype = {
createelement: function(tagname, attributes) {
var ele = document.createelement(tagname);
for (var key in attributes) {
ele.setattribute(key, attributes[key]);
}
return ele;
},
gettransparentpercent: function(ctx, width, height) {
var imgdata = ctx.getimagedata(0, 0, width, height),
pixles = imgdata.data,
transpixs = [];
for (var i = 0, j = pixles.length; i < j; i += 4) {
var a = pixles[i + 3];
if (a < 128) {
transpixs.push(i);
}
}
return (transpixs.length / (pixles.length / 4) * 100).tofixed(2);
},
resizecanvas: function(canvas, width, height) {
canvas.width = width;
canvas.height = height;
canvas.getcontext('2d').clearrect(0, 0, width, height);
},
resizecanvas_w: function(canvas, width, height) {
canvas.width = width;
canvas.height = height;
canvas.getcontext('2d').clearrect(0, 0, width, height);
if (this.vail) this.drawlottery();
else this.drawmask();
},
drawpoint: function(x, y, fresh) {
this.maskctx.beginpath();
this.maskctx.arc(x, y, 20, 0, math.pi * 2);
this.maskctx.fill();
this.maskctx.beginpath();
this.maskctx.linewidth = 60;
this.maskctx.linecap = this.maskctx.linejoin = 'round';
if (this.lastposition) {
this.maskctx.moveto(this.lastposition[0], this.lastposition[1]);
}
this.maskctx.lineto(x, y);
this.maskctx.stroke();
this.lastposition = [x, y];
this.mask.style.zindex = (this.mask.style.zindex == 20) ? 21 : 20;
},
bindevent: function() {
var _this = this;
var device = (/android|webos|iphone|ipad|ipod|blackberry|iemobile|opera mini/i.test(navigator.useragent.tolowercase()));
var clickevtname = device ? 'touchstart' : 'mousedown';
var moveevtname = device ? 'touchmove' : 'mousemove';
if (!device) {
var ismousedown = false;
_this.connode.addeventlistener('mouseup', function(e) {
e.preventdefault();
ismousedown = false;
var per = _this.gettransparentpercent(_this.maskctx, _this.width, _this.height);
if (per >= 80) {//在大于等于80%的时候调用回调函数
if (typeof(_this.drawpercentcallback) == 'function') _this.drawpercentcallback();
}
}, false);
} else {
_this.connode.addeventlistener("touchmove", function(e) {
if (ismousedown) {
e.preventdefault();
}
if (e.cancelable) {
e.preventdefault();
} else {
window.event.returnvalue = false;
}
}, false);
_this.connode.addeventlistener('touchend', function(e) {
ismousedown = false;
var per = _this.gettransparentpercent(_this.maskctx, _this.width, _this.height);
if (per >= 80) {//在大于等于80%的时候调用回调函数
if (typeof(_this.drawpercentcallback) == 'function') _this.drawpercentcallback();
}
}, false);
}
this.mask.addeventlistener(clickevtname, function(e) {
e.preventdefault();
ismousedown = true;
var x = (device ? e.touches[0].pagex : e.pagex || e.x);
var y = (device ? e.touches[0].pagey : e.pagey || e.y);
_this.drawpoint(x, y, ismousedown);
}, false);
this.mask.addeventlistener(moveevtname, function(e) {
e.preventdefault();
if (!ismousedown) return false;
e.preventdefault();
var x = (device ? e.touches[0].pagex : e.pagex || e.x);
var y = (device ? e.touches[0].pagey : e.pagey || e.y);
_this.drawpoint(x, y, ismousedown);
}, false);
},
drawlottery: function() {
if (this.lotterytype == 'image') {
var image = new image(),
_this = this;
image.onload = function() {
this.width = _this.width;
this.height = _this.height;
_this.resizecanvas(_this.background, _this.width, _this.height);
_this.backctx.drawimage(this, 0, 0, _this.width, _this.height);
_this.drawmask();
}
image.src = this.lottery;
} else if (this.lotterytype == 'text') {
this.width = this.width;
this.height = this.height;
this.resizecanvas(this.background, this.width, this.height);
this.backctx.save();
this.backctx.fillstyle = '#fff';
this.backctx.fillrect(0, 0, this.width, this.height);
this.backctx.restore();
this.backctx.save();
var fontsize = 30;
this.backctx.font = 'bold ' + fontsize + 'px arial';
this.backctx.textalign = 'center';
this.backctx.fillstyle = '#f60';
this.backctx.filltext(this.lottery, this.width / 2, this.height / 2 + fontsize / 2);
this.backctx.restore();
this.drawmask();
}
},
drawmask: function() {
if (this.covertype == 'color') {
this.maskctx.fillstyle = this.cover;
this.maskctx.fillrect(0, 0, this.width, this.height);
this.maskctx.globalcompositeoperation = 'destination-out';
} else if (this.covertype == 'image') {
var image = new image(),
_this = this;
image.onload = function() {
_this.resizecanvas(_this.mask, _this.width, _this.height);
var android = (/android/i.test(navigator.useragent.tolowercase()));
_this.maskctx.globalalpha = 1;//上面一层的透明度，1为不透明
_this.maskctx.drawimage(this, 0, 0, this.width, this.height, 0, 0, _this.width, _this.height);
//---以下一段为在上面一层上写字
// var fontsize = 50;
// var txt = '123123';
// var gradient = _this.maskctx.createlineargradient(0, 0, _this.width, 0);
// gradient.addcolorstop("0", "#fff");
// gradient.addcolorstop("1.0", "#000");
// _this.maskctx.font = 'bold ' + fontsize + 'px arial';
// _this.maskctx.textalign = 'left';
// _this.maskctx.fillstyle = gradient;
// _this.maskctx.filltext(txt, _this.width / 2 - _this.maskctx.measuretext(txt).width / 2, 100);
// _this.maskctx.globalalpha = 1;
_this.maskctx.globalcompositeoperation = 'destination-out';
}
image.src = this.cover;
}
},
init: function(lottery, lotterytype) {
if (lottery) {
this.lottery = lottery;
this.lottery.width = this.width;
this.lottery.height = this.height;
this.lotterytype = lotterytype || 'image';
this.vail = true;
}
if (this.vail) {
this.background = this.background || this.createelement('canvas', {
style: 'position:fixed;top:0;left:0;background-color:transparent;'
});
}
this.mask = this.mask || this.createelement('canvas', {
style: 'position:fixed;top:0;left:0;background-color:transparent;'
});
this.mask.style.zindex = 20;
if (!this.connode.innerhtml.replace(/[\w\w]| /g, '')) {
if (this.vail) this.connode.appendchild(this.background);
this.connode.appendchild(this.mask);
this.bindevent();
}
if (this.vail) this.backctx = this.backctx || this.background.getcontext('2d');
this.maskctx = this.maskctx || this.mask.getcontext('2d');
if (this.vail) this.drawlottery();
else this.drawmask();
var _this = this;
window.addeventlistener('resize', function() {
_this.width = document.documentelement.clientwidth;
_this.height = document.documentelement.clientheight;
_this.resizecanvas_w(_this.mask, _this.width, _this.height);
}, false);
}
}
另一个zepto.js是库函数文件，可网上自行查找
出来的效果如图
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持移动技术网。
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