Not sure it can help:
I use this to get the native screen resolution:
global Sw,Sh
load dll "user32.dll",1
Sw=call dll(1,"GetSystemMetrics",0)
Sh=call dll(1,"GetSystemMetrics",1)
delete dll 1
set display mode Sw,Sh,32,1
rem Sw=1920:Sh=1080
rem set display mode Sw,Sh,32,1
But you could force the Sw , Sh values (rem lines) avoiding the dll part, or have the players choose theirs at start.. Or allow several options based on most common screen resolutions .
Or calculate the correct aspect ratio : get the user screen resolution and adjust the width (for instance 1080/1920 =0.5626 ) like :
global Sw#,Sh#
load dll "user32.dll",1
Sw#=call dll(1,"GetSystemMetrics",0)
Sh#=call dll(1,"GetSystemMetrics",1)
delete dll 1
Sw#=Sw#*0.5626
set display mode Sw#,Sh#,32,1
Just few ideas.