摄像机按层渲染
Camera.cullingMask = 1<<x;//渲染x层
Camera.cullingMask = ~(1<<x);//渲染除去x的所有层
Camera.cullingMask &= ~(1<<x);//关闭层x
Camera.cullingMask |= (1<<x);//打开层x
Camera.cullingMask = (1<<x) + (1<<y) + (1<<z);//摄像机只显示x,y,z层。
CullingMask = 0//nothing
CullingMask = -1//everything
