HTML5+CSS3实例 ：canvas 模拟实现电子彩票刮刮乐代码

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：

  
  
  
      
      
  
      
      
  
      
  
      
      
  
  
 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;  
 }  
  
      
  
  
  
  
  
      
      
  
  
  
  
  

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：

  
  
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";  
  
  
      
    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);  
 }  
    };  
  
      
    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();  
    }  
      
    $(window).resize(function ()  
    {  
 pageOffset = $canvas.offset();  
    });  
  
      
    this.getCanvasPoint = function (pageX, pageY)  
    {  
 return{  
     x: pageX - pageOffset.left,  
     y: pageY - pageOffset.top  
 }  
    }  
      
    this.clearRect = function (start)  
    {  
 context.clearRect(start.x, start.y, 10, 10);  
 return this;  
    };  
  
      
    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);  
 }  
    };  
      
    this.penWidth = function (newWidth)  
    {  
 if (arguments.length)  
 {  
     context.lineWidth = newWidth;  
     return this;  
 }  
 return context.lineWidth;  
    };  
  
      
    this.penColor = function (newColor)  
    {  
 if (arguments.length)  
 {  
     context.strokeStyle = newColor;  
     context.fillStyle = newColor;  
     return this;  
 }  
  
 return context.strokeStyle;  
    };  
  
      
    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

  
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,  
      
    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

  
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,  
      
    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考高分网。