该帧开始以来的时间（只读）。此为自加载上一个关卡以来的时间（以秒为单位）。
This is the time in seconds since the last level was loaded. This is Read-Only. Double precision version of timeSinceLevelLoad. This offers more precision than a float or single value, particularly over extended periods of real-world time. In almost all cases, choose the timeSinceLevelLoadAsDouble equivalent over timeSinceLevelLoad.