HTML5+CSS3实例 ：canvas 模拟实现电子彩票刮刮乐代码

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;  

/** 
 * 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;  
    }  
};