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js canvas實(shí)現(xiàn)橡皮擦效果

更新時(shí)間：2018年12月20日 14:52:13 作者：snow_finland

這篇文章主要為大家詳細(xì)介紹了使用Canvas實(shí)現(xiàn)橡皮擦效果，具有一定的參考價(jià)值，感興趣的小伙伴們可以參考一下

本文實(shí)例為大家分享了canvas實(shí)現(xiàn)橡皮擦效果的具體代碼，供大家參考，具體內(nèi)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：上面一層的圖片地址，coverType：'image'or'color'，width：canvas寬, height：canvas高, drawPercentCallback：回調(diào)函數(shù)
 //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%的時(shí)候調(diào)用回調(diào)函數(shù)
     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%的時(shí)候調(diào)用回調(diào)函數(shù)
     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;//上面一層的透明度，1為不透明
    _this.maskCtx.drawImage(this, 0, 0, this.width, this.height, 0, 0, _this.width, _this.height);
 
    //---以下一段為在上面一層上寫(xiě)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);
 }
}

另一個(gè)zepto.js是庫(kù)函數(shù)文件，可網(wǎng)上自行查找

出來(lái)的效果如圖