Google Chrome 设备工具栏原理

1.不同预览模式

2.计算出缩放比

3.固定滚动偏移

关键代码：

overview：

ratioW = getChildRect().width / getParentRect().width

ratioH = getChildRect().height / getParentRect().height

maxRatio = max(ratioW, ratioH)

if(maxRatio < 1)

return 1

else

return 1/maxRatio

oldViewCenter = viewCenterOffset

real:

       if(bInit) { // 重置
           if(childOutline.height < parentOutline.height)
               oldViewCenter.fY = viewCenterOffset.fY;
           else
               oldViewCenter.fY = viewCenterOffset.fY + (childOutline.height - parentOutline.height) / 2; //顶部对齐
       } else { // 滚动后拉伸
           if(refParentOutline.top >= refChildOutline.top) //上次就无溢出
               oldViewCenter.fY = viewCenterOffset.fY + (childOutline.height - parentOutline.height) / 2; //顶部对齐
           else {
               overflowLen = refParentOutline.top - refChildOutline.top //溢出长度
               if(childOutline.height - overflowLen <= parentOutline.height)   //溢出后下面留白
                   oldViewCenter.fY = parentOutline.bottom - childOutline.bottom // 底部对齐
               else
                   oldViewCenter.fY = parentOutline.top - overflowLen - childOutline.top // 顶部溢出对齐
           }

}