HTML5/CSS3专题 canvas 模拟实现电子彩票刮刮乐示例代码（图）-H5教程

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>

<p class="container">
    <canvas id="back" width="200" height="80"></canvas>
    <canvas id="front" width="200" height="80"></canvas>
</p>


</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;
    }
}

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