let DANMAKU_SPEED: CGFloat =     // 弹幕每秒移动速度

    let DANMAKU_SPACE_TIME: NSTimeInterval =     // 弹幕之间的时间间隔

    let DANMAKU_MAX_ROW =     // 最多同时弹幕行数

    let danmakuFont = UIFont.systemFontOfSize()    // 弹幕字体大小

    var rowArray = Array<Array<Danmaku>>(count: , repeatedValue: Array<Danmaku>())

    var danmakuQueue = NSOperationQueue()    // 队列

    class Danmaku : NSObject{

        var msg: Msg

        var view: UILabel?

        var size = CGSize(width: , height: )

        var row =

        var startTime: NSDate?

        var duration: NSTimeInterval =

        var delay: NSTimeInterval = 

        init(_ msg: Msg, _ row: Int, _ delay: NSTimeInterval = ) {

            self.msg = msg

            self.row = row

            self.delay = delay

        }

    }

    func queueDanmaku(msg: Msg) {

        danmakuQueue.addOperation(NSBlockOperation(block: { [weak self] in

            if let weakself = self {

                repeat {

                    //检测放第几行

                    for var row = ; row < weakself.DANMAKU_MAX_ROW; ++row {

                        let rowDanmaku = weakself.rowArray[row]

                        if rowDanmaku.count ==  {

                            let danmaku = Danmaku(msg, weakself.danmakuFont, row)

                            weakself.rowArray[row].append(danmaku)

                            self?.performSelectorOnMainThread("sendDanmaku:", withObject: danmaku, waitUntilDone: true)

                            return

                        } else {

                            if let lastDanmaku = rowDanmaku.last {

                                if let startTime = lastDanmaku.startTime {

                                    let now = NSDate()

                                    let seconds = now.timeIntervalSinceDate(startTime)

                                    let widthDuration = Double(lastDanmaku.size.width / weakself.DANMAKU_SPEED)

                                    var delay = seconds - weakself.DANMAKU_SPACE_TIME - widthDuration

                                    if delay >=  {

                                        delay =

                                    } else {

                                        if lastDanmaku.delay > lastDanmaku.duration {

                                            continue

                                        }

                                    }

                                    let danmaku = Danmaku(msg, weakself.danmakuFont, row, abs(delay) + lastDanmaku.delay)

                                    weakself.rowArray[row].append(danmaku)

                                    self?.performSelectorOnMainThread("sendDanmaku:", withObject: danmaku, waitUntilDone: true)

                                    return

                                }

                            }

                        }

                    }

                    sleep()

                } while self != nil

            }

            }))

    }

    func sendDanmaku(danmaku: Danmaku) {

        let text = "\(danmaku.msg.user_name) : \(danmaku.msg.text)"

        let size = NSString(string: text).sizeWithAttributes([NSFontAttributeName : danmakuFont])

        let width = UIScreen.mainScreen().bounds.size.width

        let top =  + danmaku.row * (Int(size.height) + )

        let label = UILabel(frame: CGRectMake(width, CGFloat(top), size.width, size.height))

        let duration = (width + size.width) / DANMAKU_SPEED

        danmaku.view = label

        danmaku.size = size

        danmaku.startTime = NSDate()

        danmaku.duration = NSTimeInterval(duration)

        label.text = text

        label.font = danmakuFont

        label.textColor = UIColor.whiteColor()

        label.shadowColor = UIColor.blackColor()

        label.shadowOffset = CGSizeMake(, -1.0)

        self.view.addSubview(label)

        UIView.animateWithDuration(Double(duration), delay: danmaku.delay, options: UIViewAnimationOptions.CurveLinear, animations: { () -> Void in

                label.left = -label.width

            }) { [weak self] (Bool) -> Void in

                if !(self?.rowArray[danmaku.row].isEmpty ?? true) {

                    self?.rowArray[danmaku.row].removeFirst()

                }

                label.removeFromSuperview()

        }

    }