首页
所有分类
TAGS
文字工具 EMOJI BIBLE
编程 Javascript

js canvas实现橡皮擦效果

Posted in Javascript onDecember 20, 2018

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

js canvas实现橡皮擦效果

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三水点靠木。

js canvas实现橡皮擦效果

- Author -

snow_finland

声明：登载此文出于传递更多信息之目的，并不意味着赞同其观点或证实其描述。

Javascript 相关文章推荐
基于jquery的图片的切换(以数字的形式)
Feb 14 Javascript
深入理解JavaScript系列(9) 根本没有“JSON对象”这回事！
Jan 15 Javascript
js 判断上传文件大小及格式代码
Nov 13 Javascript
setInterval与clearInterval的使用示例代码
Jan 28 Javascript
jQuery动态效果显示人物结构关系图的方法
May 07 Javascript
原生javascript实现图片无缝滚动效果
Feb 12 Javascript
Bootstrap select实现下拉框多选效果
Dec 23 Javascript
js实现自动轮换选项卡
Jan 13 Javascript
Vue2.x中利用@font-size引入字体图标报错的解决方法
Sep 28 Javascript
JavaScript常用8种数组去重代码实例
Sep 09 Javascript
JavaScript封装单向链表的示例代码
Sep 17 Javascript
使用Vue实现一个树组件的示例
Nov 06 Javascript
浅谈VueJS SSR 后端绘制内存泄漏的相关解决经验
Dec 20 #Javascript
Cocos2d实现刮刮卡效果
Dec 20 #Javascript
浅谈Fetch 数据交互方式
Dec 20 #Javascript
cocos2dx+lua实现橡皮擦功能
Dec 20 #Javascript
element-ui table span-method(行合并)的实现代码
Dec 20 #Javascript
fetch 如何实现请求数据
Dec 20 #Javascript
JS闭包经典实例详解
Dec 20 #Javascript
南麂列岛(1) 直流胆(1) S2000(3) 森海(1) MX500(1) 1 Tube Radio(1) YB400(2) 台湾(1) YB217(1) YB235(1)
You might like
destoon二次开发入门示例
2014/06/20 PHP
PHP设置进度条的方法
2015/07/08 PHP
Laravel重写用户登录简单示例
2016/10/08 PHP
PHP验证终端类型是否为手机的简单实例
2017/02/07 PHP
laravel自定义分页的实现案例offset()和limit()
2019/10/15 PHP
javascript实现上传图片前的预览（TX的面试题）
2007/08/20 Javascript
JavaScript 学习笔记（七）字符串的连接
2009/12/31 Javascript
js中top、clientTop、scrollTop、offsetTop的区别 文字详细说明版
2011/01/08 Javascript
Javascript 是你的高阶函数(高级应用)
2015/06/15 Javascript
有关json_decode乱码及NULL的问题
2015/10/13 Javascript
基于javascript制作经典传统的拼图游戏
2016/03/22 Javascript
JavaScript中日常收集常见的10种错误(推荐)
2017/01/08 Javascript
webpack 样式加载的实现原理
2018/06/12 Javascript
了解JavaScript表单操作和表单域
2019/05/27 Javascript
js实现经典贪吃蛇小游戏
2020/03/19 Javascript
jQuery+Ajax+js实现请求json格式数据并渲染到html页面操作示例
2020/06/02 jQuery
nodejs中内置模块fs,path常见的用法说明
2020/11/07 NodeJs
[01:28]2014DOTA2国际邀请赛中国区预选赛四大豪门直升机抵达会场
2014/05/24 DOTA
[02:05]2014DOTA2西雅图国际邀请赛 BBC第二天小组赛总结
2014/07/11 DOTA
[49:05]OG vs Newbee 2019DOTA2国际邀请赛淘汰赛 胜者组 BO3 第二场 8.21.mp4
2020/07/19 DOTA
python 自动提交和抓取网页
2009/07/13 Python
利用Python和OpenCV库将URL转换为OpenCV格式的方法
2015/03/27 Python
对pandas replace函数的使用方法小结
2018/05/18 Python
python 调用钉钉机器人的方法
2019/02/20 Python
Python3.5基础之NumPy模块的使用图文与实例详解
2019/04/24 Python
新电JAVA笔试题目
2014/08/31 面试题
什么是Linux虚拟文件系统VFS
2012/01/31 面试题
医学生自荐信范文
2013/12/03 职场文书
质检员岗位职责
2013/12/17 职场文书
销售辞职报告范文
2014/01/12 职场文书
高中化学教学反思
2014/01/13 职场文书
高中生自我评语大全
2014/01/19 职场文书
四风问题个人对照检查剖析材料
2014/09/27 职场文书
预备党员群众路线教育实践活动思想汇报2014
2014/10/25 职场文书
2015年主婚人婚礼致辞
2015/07/28 职场文书
vue项目多环境配置(.env)的实现
2021/07/21 Vue.js