Start by downloading PrBoom or an equivalent. PrBoom is nice in that it supports Windows and Linux equally well. Windows installation is as easy as downloading the latest Windows ZIP archive (2.2.4 at the time of writing) and unzipping it into an appropriate directory.

If you have the registered version of DOOM somewhere,^[17] copy its .wad files into the PrBoom directory. Otherwise, look for a file called doom1.wad online. This is the shareware version.

DOOM stores all its maps, images, and sounds in WAD files. There are two types. IWADs are the original internal WADs shipped with the game; they contain the default game information. PWADs are player-supplied WADs that change or add parts of the game. They can be much smaller, because anything they don’t supply directly comes from the original IWAD.

Think of a WAD as a directory containing subdirectories and files, somewhat like a ZIP archive. To replace a particular graphic, you have to know its details within the IWAD and add an equivalent graphic to your PWAD. That’s where tools such as DeuTex (http://www.teaser.fr/~amajorel/deutex/) come in.

DeuTex is a WAD disassembler, meaning that it can disassemble a WAD into a real directory. It runs on DOS and Linux. Download and extract DeuTex into its own directory, then extract the data from doom.wad with a command resembling:

$ ./deutex -extract /usr/share/games/doom/doom.wad

This creates several directories such as textures/ and sounds/ as well as a file called wadinfo.txt.

Besides trial and error, there’s really no good way to figure out which image within this WAD to replace. Fortunately, I can tell you that the files in graphics/stf* represent the face in the status bar. I replaced the god-mode powerup image (type iddqd while playing) with a picture of my nephew. DeuTex extracts this image to graphics/stfgod0.pnm.

The trickiest part of this process is building a 24 29 image that looks good in DOOM, especially with its restricted palette. I cropped and adjusted the picture until it fit, then saved it as a 256-color GIF file in graphics/stfgod0.gif. Be sure to keep the same base name as the file you’re replacing; otherwise, DOOM won’t know how to find the resource. It’s okay to use a different file extension; DeuTex converts BMP, GIF, or JPEG files to PPM files automatically when it builds a WAD. If you do use a different extension, though, be sure to move the original file out of the way so that DeuTex will use your replacement.

The next step is to build a manifest file to tell DeuTex which files to assemble. Open the wadinfo.txt file in your favorite text editor. It has several internal sections for the different types of files within the WAD. Delete everything that you haven’t replaced. In my case, I had a very short file:

# List of Pictures (with insertion point)
[graphics]
STFGOD0 -5      -2

Be sure to keep the [graphics] heading, though you can delete the entries beneath it for the images you want to stay the same. Save the file with a different name, perhaps godinfo.txt, so you can make other modifications by copying the relevant lines from the original manifest.

The final step is to assemble all the new resources into a PWAD. DeuTex again can do this. Use a command resembling:

$ ./deutex -build godinfo.txt baby.wad

If everything goes well, this will write a new PWAD called baby.wad in your current directory. DeuTex helpfully refuses to overwrite an existing file, so delete or move baby.wad if you’ve already generated one.

To see the effects of your work, launch PrBoom with your new PWAD. Use the -file switch to give the location of the file:

$ prboom -file baby.wad

Start a new game, type iddqd, and marvel at the connection between innocence and ultimate power, seen in Figure 7-4.

Figure 7-4. An alternate god-mode image

The same technique here works for replacing any image or sound within the IWAD files, including monsters and weapons. Remember, if you can do it for one image, you can do it for many.