Laya 使list渲染支持分帧的思路

Laya 使list渲染支持分帧的思路

@author ixenos 2019-09-06

1.由于Laya的list渲染时没有做分帧处理，只做了延迟帧处理，所以当单页元素较多时，会有大量运算卡帧的情况，

结合之前 Laya 分帧加载优化 这篇文章，对其中renderItems做出优化

2.原renderItems：

         /**
          * @private
          * 渲染单元格列表。
          */
         protected function renderItems(from:int = 0, to:int = 0):void {
             for (var i:int = from, n:int = to || _cells.length; i < n; i++) {
                 renderItem(_cells[i], _startIndex + i);
             }
             changeSelectStatus();
         }

3.分帧方案：

         private var _latterFrom:int = 0;
         private var _latterTo:int = 0;
         protected function renderItems(from:int = 0, to:int = 0):void {
             _latterFrom = from;
             _latterTo = to;
             Laya.timer.clear(this, onLatterFrames);
             Laya.timer.frameLoop(1, this, onLatterFrames);
         }

         private var _renderSt:Number = 0;
         private var _renderTLimit:Number = 0;
         public var latterFrameRatio:Number = 0.8;//运行时脚本占帧时间比，这个用来调优 --ixenos
         protected function onLatterFrames():void {
             _renderTLimit = 1000/60*latterFrameRatio;
             _renderSt = new Date().getTime();
             _latterTo = _latterTo>0?_latterTo:_cells.length;
             for (var i:int = _latterFrom; i < _latterTo; i++) {
                 var curT:Number = new Date().getTime();
                 if(curT - _renderSt > _renderTLimit){
                     _latterFrom = i;//暂存进度
                     return;
                 }
                 renderItem(_cells[i], _startIndex + i);
                 changeCellState(_cells[i], _selectedIndex === _startIndex + i, 1);
             }
             Laya.timer.clear(this, onLatterFrames);
         }