1.9.0 introduces virtual directory mappings (abbrev. VDM), which allow you to make the contents of one directory appear inside another directory at runtime. For example, you could have a directory called MyAuto with a set of data files somewhere on your hard drive. You could map this directory to Data/<Game>/Auto, which would cause MyAuto to behave as though it was an auto-loading directory.

A virtual directory mapping is defined using the -vdmap option. It takes the source and destination directories as parameters. For example:

-vdmap "D:\Games\MyAuto" "C:\Doomsday\Data\jDoom\Auto"

You can define an unlimited number of virtual directory mappings using multiple -vdmap options.

Note, however, that -vdmap only affects real files. It does not affect virtual files in pk3s or anywhere else. The virtual directory mappings are tried when all other methods of finding a file have failed. So, all real files and virtual_files override the VDMs.