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
jquery form表单提交插件asp.net后台中文解码
Jun 12 Javascript
jQuery的运行机制和设计理念分析
Apr 05 Javascript
通过pjax实现无刷新翻页(兼容新版jquery)
Jan 31 Javascript
如何使用HTML5地理位置定位功能
Apr 27 Javascript
Javascript小技能总结(推荐)
Jun 02 Javascript
关于Bootstrap按钮组件消除黄框的方法
May 19 Javascript
vue中如何创建多个ueditor实例教程
Nov 14 Javascript
轻松搞定jQuery+JSONP跨域请求的解决方案
Mar 06 jQuery
详解vue.js下引入百度地图jsApi的两种方法
Jul 27 Javascript
详解Vue.js自定义tipOnce指令用法实例
Dec 19 Javascript
图文讲解vue的v-if使用方法
Feb 11 Javascript
CocosCreator入门教程之网络通信
Apr 16 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
人人对战(1) 递归(1) 限速(1) tokenizer(1) 后端(1) 双人对弈(1) Parser(1) 限流(2) 内置模块(1) IP(1)
You might like
收音机另类DIY - 纸巾盒做外壳
2021/03/02 无线电
yii框架builder、update、delete使用方法
2014/04/30 PHP
php事务处理实例详解
2014/07/11 PHP
如何使用PHP给图片加水印
2016/10/12 PHP
php格式文件打开的四种方法
2018/02/24 PHP
js树形控件脚本代码
2008/07/24 Javascript
用Javascript实现锚点(Anchor)间平滑跳转
2009/09/08 Javascript
用jquery设置按钮的disabled属性的实现代码
2010/11/28 Javascript
使用按钮控制以何种方式打开新窗口的属性介绍
2012/12/17 Javascript
jquery插件validate验证的小例子
2013/05/08 Javascript
JS事件在IE与FF中的区别详细解析
2013/11/20 Javascript
jquery实现很酷的网页顶部图标下拉菜单效果
2015/08/22 Javascript
URL的参数中有加号传值变为空格的问题(URL特殊字符)
2016/11/04 Javascript
jQuery实现鼠标跟随效果
2017/02/20 Javascript
vue绑定class与行间样式style详解
2017/08/16 Javascript
JavaScript基于对象方法实现数组去重及排序操作示例
2018/07/10 Javascript
Angular 实现输入框中显示文章标签的实例代码
2018/11/07 Javascript
详解React服务端渲染从入门到精通
2019/03/28 Javascript
jQuery实现简单评论区功能
2020/10/26 jQuery
vue2.0 watch里面的 deep和immediate用法说明
2020/10/30 Javascript
Python函数式编程指南（四）：生成器详解
2015/06/24 Python
Python实现批量读取图片并存入mongodb数据库的方法示例
2018/04/02 Python
Python读取数据集并消除数据中的空行方法
2018/07/12 Python
Python自动发送邮件的方法实例总结
2018/12/08 Python
python3安装speech语音模块的方法
2018/12/24 Python
python实现最小二乘法线性拟合
2019/07/19 Python
100行Python代码实现每天不同时间段定时给女友发消息
2019/09/27 Python
Keras SGD 随机梯度下降优化器参数设置方式
2020/06/19 Python
纯CSS3实现Material Design效果
2017/03/09 HTML / CSS
毕业生求职简历的自我评价
2013/10/23 职场文书
会计实习自我鉴定
2013/12/04 职场文书
医学生职业规划范文
2014/01/05 职场文书
企业诚信承诺书
2014/05/23 职场文书
个人公司授权委托书范本
2014/10/12 职场文书
2015年幼儿园教育教学工作总结
2015/05/25 职场文书
Python爬虫之自动爬取某车之家各车销售数据
2021/06/02 Python