Enhanced OpenGL port of the official DOOM source code that also supports
Heretic, Hexen, and Strife.

This requires fmodapi.

Optional compile-time dependency: fluidsynth (autodetected).

See below for optional runtime dependencies.

gzdoom is only a game engine. To actually play the game, you'll need
the game data (IWAD file) from one of the supported games. These include
Doom, Ultimate Doom, Final Doom, FreeDoom, Heretic, Hexen, and Strife.
Place the .wad file(s) in /usr/share/games/doom.

If you don't own any of the supported games, you can install one or more
of these slackbuilds.org packages to get a playable game:

freedoom, doom_shareware_data, heretic_shareware_data, hexen_demo_data

To hear the in-game music, there are several options. In the game menu,
select "Options | Sound Options" and set "MIDI Device" to one of the
below:

FMOD (the default) - Install ff8dls and set the console variable
snd_midipatchset to "/usr/share/sounds/dls/ff8.dls" (from the in-game
console or by editing ~/.gzdoom/zdoom.ini). Alternatively,
if you dual-boot with Windows, use something like
/dosC/windows/system32/drivers/gm.dls (replace dosC with the mountpoint
of your C: drive in Windows).

FluidSynth - Install fluidsynth (before building gzdoom) and fluid-soundfont.

Timidity - Install TiMidity++ and either eawpats or freepats, and set up
/etc/timidity/timidity.cfg to use it.

GUS or OPL - Nothing extra required; these are software emulations of
classic soundcards from the early 1990s.

While you're in the Sound Options menu, it's probably a good idea to set
"Output System" to "ALSA" (otherwise, the default will use OSS emulation).