====== Virtual directory mapping ======

[[version: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:
<code>
-vdmap "D:\Games\MyAuto" "C:\Doomsday\Data\jDoom\Auto"
</code>

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 [[pk3]]s 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_file]]s override the VDMs.