今天给大家带来一个刮刮乐的小例子~基于HTML5 canvas的，有兴趣的可以改成Android版本的，或者其他的~
效果图：
贴一张我中500w的照片，咋办啊，怎么花呢~
好了，下面开始原理：
1、刮奖区域两个Canvas，一个是front ， 一个back ，front遮盖住下面的canvas。
2、canvas默认填充了一个矩形，将下面canvas效果图遮盖，然后监听mouse事件，根据mousemove的x,y坐标，进行擦出front canvas上的矩形区域，然后显示出下面的canvas的效果图。
很简单把~嘿嘿~
1、HTML文件内容：
<!DOCTYPE html> <html> <head> <title></title> <meta charset="utf-8"> <script type="text/javascript" src="../../jquery-1.8.3.js"></script> <script type="text/javascript" src="canvas2d.js"></script> <script type="text/javascript" src="GuaGuaLe2.js"></script> <script type="text/javascript"> $(function () { var guaguale = new GuaGuaLe("front", "back"); guaguale.init({msg: "￥5000000.00"}); }); </script> <style type="text/css"> body { background: url("s_bd.jpg") repeat 0 0; } .container { position: relative; width: 400px; height: 160px; margin: 100px auto 0; background: url(s_title.png) no-repeat 0 0; background-size: 100% 100%; } #front, #back { position: absolute; width: 200px; left: 50%; top: 100%; margin-left: -130px; height: 80px; border-radius: 5px; border: 1px solid #444; } </style> </head> <body> <div class="container"> <canvas id="back" width="200" height="80"></canvas> <canvas id="front" width="200" height="80"></canvas> </div> </body> </html> 2、首先我利用了一个以前写的canvas辅助类，留下来今天要用的一些方法：
/** * Created with JetBrains WebStorm. * User: zhy * Date: 13-12-17 * Time: 下午9:42 * To change this template use File | Settings | File Templates. */ function Canvas2D($canvas) { var context = $canvas[0].getContext("2d"), width = $canvas[0].width, height = $canvas[0].height, pageOffset = $canvas.offset(); context.font = "24px Verdana, Geneva, sans-serif"; context.textBaseline = "top"; /** * 绘制矩形 * @param start * @param end * @param isFill */ this.drawRect = function (start, end, isFill) { var w = end.x - start.x , h = end.y - start.y; if (isFill) { context.fillRect(start.x, start.y, w, h); } else { context.strokeRect(start.x, start.y, w, h); } }; /** * 根据书写的文本，得到该文本在canvas上书写的中心位置的左上角坐标 * @param text * @returns {{x: number, y: number}} */ this.caculateTextCenterPos = function (text) { var metrics = context.measureText(text); console.log(metrics); // context.font = fontSize + "px Verdana, Geneva, sans-serif"; var textWidth = metrics.width; var textHeight = parseInt(context.font); return { x: width / 2 - textWidth / 2, y: height / 2 - textHeight / 2 }; } this.width = function () { return width; } this.height = function () { return height; } this.resetOffset = function () { pageOffset = $canvas.offset(); } /** * 当屏幕大小发生变化，重新计算offset */ $(window).resize(function () { pageOffset = $canvas.offset(); }); /** * 将页面上的左边转化为canvas中的坐标 * @param pageX * @param pageY * @returns {{x: number, y: number}} */ this.getCanvasPoint = function (pageX, pageY) { return{ x: pageX - pageOffset.left, y: pageY - pageOffset.top } } /** * 清除区域，此用户鼠标擦出刮奖涂层 * @param start * @returns {*} */ this.clearRect = function (start) { context.clearRect(start.x, start.y, 10, 10); return this; }; /** *将文本绘制到canvas的中间 * @param text * @param fill */ this.drawTextInCenter = function (text, fill) { var point = this.caculateTextCenterPos(text); if (fill) { context.fillText(text, point.x, point.y); } else { context.strokeText(text, point.x, point.y); } }; /** * 设置画笔宽度 * @param newWidth * @returns {*} */ this.penWidth = function (newWidth) { if (arguments.length) { context.lineWidth = newWidth; return this; } return context.lineWidth; }; /** * 设置画笔颜色 * @param newColor * @returns {*} */ this.penColor = function (newColor) { if (arguments.length) { context.strokeStyle = newColor; context.fillStyle = newColor; return this; } return context.strokeStyle; }; /** * 设置字体大小 * @param fontSize * @returns {*} */ this.fontSize = function (fontSize) { if (arguments.length) { context.font = fontSize + "px Verdana, Geneva, sans-serif"; return this; } return context.fontSize; } } 这个类也就对Canvas对象进行了简单的封装，设置参数，绘制图形什么的，比较简单，大家可以完善下这个类~
3、GuaGuaLe.js
/** * Created with JetBrains WebStorm. * User: zhy * Date: 14-6-24 * Time: 上午11:36 * To change this template use File | Settings | File Templates. */ function GuaGuaLe(idFront, idBack) { this.$eleBack = $("#" + idBack); this.$eleFront = $("#" + idFront); this.frontCanvas = new Canvas2D(this.$eleFront); this.backCanvas = new Canvas2D(this.$eleBack); this.isStart = false; } GuaGuaLe.prototype = { constructor: GuaGuaLe, /** * 将用户的传入的参数和默认参数做合并 * @param desAttr * @returns {{frontFillColor: string, backFillColor: string, backFontColor: string, backFontSize: number, msg: string}} */ mergeAttr: function (desAttr) { var defaultAttr = { frontFillColor: "silver", backFillColor: "gold", backFontColor: "red", backFontSize: 24, msg: "谢谢惠顾" }; for (var p in desAttr) { defaultAttr[p] = desAttr[p]; } return defaultAttr; }, init: function (desAttr) { var attr = this.mergeAttr(desAttr); //初始化canvas this.backCanvas.penColor(attr.backFillColor); this.backCanvas.fontSize(attr.backFontSize); this.backCanvas.drawRect({x: 0, y: 0}, {x: this.backCanvas.width(), y: this.backCanvas.height()}, true); this.backCanvas.penColor(attr.backFontColor); this.backCanvas.drawTextInCenter(attr.msg, true); //初始化canvas this.frontCanvas.penColor(attr.frontFillColor); this.frontCanvas.drawRect({x: 0, y: 0}, {x: this.frontCanvas.width(), y: this.frontCanvas.height()}, true); var _this = this; //设置事件 this.$eleFront.mousedown(function (event) { _this.mouseDown(event); }).mousemove(function (event) { _this.mouseMove(event); }).mouseup(function (event) { _this.mouseUp(event); }); }, mouseDown: function (event) { this.isStart = true; this.startPoint = this.frontCanvas.getCanvasPoint(event.pageX, event.pageY); }, mouseMove: function (event) { if (!this.isStart)return; var p = this.frontCanvas.getCanvasPoint(event.pageX, event.pageY); this.frontCanvas.clearRect(p); }, mouseUp: function (event) { this.isStart = false; } }; 通过用户传入的两个canvas的id，然后生成一个对象，进行初始化操作，设置事件。当然了也提供用户设置可选的参数，各种颜色，已经刮开后显示的信息等，通过
{ frontFillColor: "silver", backFillColor: "gold", backFontColor: "red", backFontSize: 24, msg: "谢谢惠顾" };传给init方法进行设置。
好了，然后就基本完工了，测试一下：
基本实现了刮开图层，但是存在一个小问题，就是当用户滑动特别快时，会出现一些断点，当然也可以忽略，不过我们准备提供一下解决方案：
产生原因：由于鼠标移动速度过快，产生的断点；解决方案：将mousemove中两次的鼠标左边，进行拆分成多个断点坐标：
如上图，把两点之间进行连线，根据斜率，然后分成多个小段，分别获得线段上的坐标（有四种可能，有兴趣可以画画图，计算下，代码如下）：
var k; if (p.x > this.startPoint.x) { k = (p.y - this.startPoint.y) / (p.x - this.startPoint.x); for (var i = this.startPoint.x; i < p.x; i += 5) { this.frontCanvas.clearRect({x: i, y: (this.startPoint.y + (i - this.startPoint.x) * k)}); } } else { k = (p.y - this.startPoint.y) / (p.x - this.startPoint.x); for (var i = this.startPoint.x; i > p.x; i -= 5) { this.frontCanvas.clearRect({x: i, y: (this.startPoint.y + ( i - this.startPoint.x ) * k)}); } } this.startPoint = p; 4、最后贴一下完整的GuaGuaLe.js
/** * Created with JetBrains WebStorm. * User: zhy * Date: 14-6-24 * Time: 上午11:36 * To change this template use File | Settings | File Templates. */ function GuaGuaLe(idFront, idBack) { this.$eleBack = $("#" + idBack); this.$eleFront = $("#" + idFront); this.frontCanvas = new Canvas2D(this.$eleFront); this.backCanvas = new Canvas2D(this.$eleBack); this.isStart = false; } GuaGuaLe.prototype = { constructor: GuaGuaLe, /** * 将用户的传入的参数和默认参数做合并 * @param desAttr * @returns {{frontFillColor: string, backFillColor: string, backFontColor: string, backFontSize: number, msg: string}} */ mergeAttr: function (desAttr) { var defaultAttr = { frontFillColor: "silver", backFillColor: "gold", backFontColor: "red", backFontSize: 24, msg: "谢谢惠顾" }; for (var p in desAttr) { defaultAttr[p] = desAttr[p]; } return defaultAttr; }, init: function (desAttr) { var attr = this.mergeAttr(desAttr); //初始化canvas this.backCanvas.penColor(attr.backFillColor); this.backCanvas.fontSize(attr.backFontSize); this.backCanvas.drawRect({x: 0, y: 0}, {x: this.backCanvas.width(), y: this.backCanvas.height()}, true); this.backCanvas.penColor(attr.backFontColor); this.backCanvas.drawTextInCenter(attr.msg, true); //初始化canvas this.frontCanvas.penColor(attr.frontFillColor); this.frontCanvas.drawRect({x: 0, y: 0}, {x: this.frontCanvas.width(), y: this.frontCanvas.height()}, true); var _this = this; //设置事件 this.$eleFront.mousedown(function (event) { _this.mouseDown(event); }).mousemove(function (event) { _this.mouseMove(event); }).mouseup(function (event) { _this.mouseUp(event); }); }, mouseDown: function (event) { this.isStart = true; this.startPoint = this.frontCanvas.getCanvasPoint(event.pageX, event.pageY); }, mouseMove: function (event) { if (!this.isStart)return; var p = this.frontCanvas.getCanvasPoint(event.pageX, event.pageY); this.frontCanvas.clearRect(p); }, mouseUp: function (event) { this.isStart = false; } }; 源码点击下载：demo
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。
![web前端开发规范文档(2014年版本)]("xxx.png)
![详解css中的float]("images/header.jpg)
