
## 抽奖类型

- 圆形抽奖
- 方形抽奖
- 老虎机
- 刮刮卡


### 圆形抽奖

代码如下：
``` javascript

	// prefix补全
	var CSSTransform = (function() {
	    var _elementStyle = document.createElement("div").style;
	    var _vendor = (function() {
	        var vendors = ["t", "webkitT", "MozT", "msT", "OT"],
	            transform,
	            i = 0,
	            l = vendors.length;
	        for (; i < l; i++) {
	            transform = vendors[i] + "ransform";
	            if (transform in _elementStyle) return vendors[i].substr(0, vendors[i].length - 1);
	        }
	        return false;
	    })();
	
	    function _prefixStyle(style) {
	        if (_vendor === false) return false;
	        if (_vendor === "") return style;
	        return _vendor + style.charAt(0).toUpperCase() + style.substr(1);
	    }
	    return _prefixStyle("transform");
	})();

	// 转盘旋转效果
	var Lottery = function(el) {
	    this.running = false;
	    this.el = $(el)[0];
	    /*
	    旋转转盘至指定位置
	    参数：
	    giftIndex: 礼物的索引（从0开始到数组.length - 1）
	    endCallback：转盘旋转完成时的回调
	    */
	    this.rotateToGift = function(giftIndex, endCallback) {
	        if (typeof(endCallback) != "function")
	            return;
	        if (giftIndex < 0 || giftIndex > CNST_GIFTS.length - 1)
	            return;
	        if (this.running)
	            return;
	        this.running = true;
	        var degToRotate = ((giftIndex + 1) * 45) + (360 * 3) - 22.5; //最少转3圈
	        var rotatedDeg = 0;
	        var speed = 20; //deg
	        var speedRatio = 1;
	        var _this = this;
	
	        function r() {
	            _this.el.style[CSSTransform] = "rotate(" + (-rotatedDeg) + "deg)";
	            rotatedDeg += (speed * speedRatio);
	            if (rotatedDeg + 180 >= degToRotate) //开始减速
	                speedRatio = (degToRotate - rotatedDeg) / 180;
	            if (rotatedDeg >= degToRotate - 0.5) {
	                rotatedDeg = degToRotate;
	                _this.el.style[CSSTransform] = "rotate(" + (-rotatedDeg) + "deg)";
	                _this.running = false;
	                endCallback();
	            } else
	                setTimeout(r, 1000 / 24);
	        };
	        r();
	    };
	};
```

**使用方法：**

``` html
<div class="lottery">
	<div class="lottery-bg"></div>
	<button id="btnStart" class="button start" onClick="startLottery()"></button>
</div>

```

调用方法：
``` javascript

var myLottery = new Lottery($(".lottery .lottery-bg"));//初始化转盘
myLottery.rotateToGift(giftIndex, function() {
	    //giftIndex为后端接口下发的奖品ID，function为回调函数
}
```
待续

移动端抽奖