IOS 实现简单的弹幕功能

let DANMAKU_SPEED: CGFloat = 150 // 弹幕每秒移动速度 let DANMAKU_SPACE_TIME: NSTimeInterval = 1 // 弹幕之间的时间间隔 let DANMAKU_MAX_ROW = 3 // 最多同时弹幕行数 let danmakuFont = UIFont.systemFontOfSize(18) // 弹幕字体大小 var rowArray = Array<Array<Danmaku>>(count: 3, repeatedValue: Array<Danmaku>())  var danmakuQueue = NSOperationQueue() // 队列 class Danmaku : NSObject{  var msg: Msg  var view: UILabel?  var size = CGSize(width: 0, height: 0)  var row = 0  var startTime: NSDate?  var duration: NSTimeInterval = 0  var delay: NSTimeInterval = 0    init(_ msg: Msg, _ row: Int, _ delay: NSTimeInterval = 0) {   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 = 0; row < weakself.DANMAKU_MAX_ROW; ++row {      let rowDanmaku = weakself.rowArray[row]      if rowDanmaku.count == 0 {       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 >= 0 {          delay = 0         } 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(1000)    } 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 = 54 + danmaku.row * (Int(size.height) + 10)  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(0, -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()  } }