DD_DIREC is a special lump recognised only by Doomsday. It contains a table that translates file paths to lump names. An example is shown below:
FILE001 /Md2/jDoom/Some.md2 FILE002 Another.ded
Using DD_DIREC it is possible to include any files that Doomsday supports inside a WAD. For instance models and hires textures can be placed inside a WAD. There is one exception to that - Demos (which are compressed with the LZSS library) must always be loaded from real files.
Each line in DD_DIREC contains a lump/path pair. The paths that begin with a (back)slash are interpreted as paths that start from the Doomsday base directory (set with -basedir; e.g. C:\Doomsday) and paths that don't begin with a (back)slash are located in the runtime_directory. The engine will first search the DD_DIRECs before opening any file for reading.
Wadtool is a simple utility for automatically creating a WAD file that contains the current directory and all its subdirectories plus a DD_DIREC lump that has (with a high probability) a unique lump name for each file. You could invoke the utility like this:
wadtool myfiles.wad /Data/jDoom/Textures/
This would create a WAD file that contains all the files from the current directory. When writing the DD_DIREC table, the prefix “/Data/jDoom/Textures/” would be added to each file name.