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>
<  http-equiv=\"Content-Type\" content=\"text/html\" charset=\"utf-8\" />
<  name=\"viewport\" content=\"initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no\" /> 
< >My Canvas 0.1</ >
<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>
<  type=\"text/ \" src=\"js/zepto.js\"></ >
<  type=\"text/ \" src=\"js/lottery.js\"></ >
<  type=\"text/ \">
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();
});
</ >
</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.  = 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.  = 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

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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脚本之家。

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