好的，我们找到了答案.

ok, we found the answers.

有一个单元 FMX.Platform 可以提供非常重要的数据.

There is unit FMX.Platform that procides quite vital data.

var
 ScreenSvc: IFMXScreenService;
begin
 if TPlatformServices.Current.SupportsPlatformService(IFMXScreenService, IInterface(ScreenSvc)) then
begin
   <your code>
 end;
end;

结果值为:

 ScreenSvc.GetScreenSize.X
 ScreenSvc.GetScreenSize.Y  
 ScreenSvc.GetScreenScale