FREQUENTLY ASKED QUESTIONS:

QUESTION #1: WHAT IS COMPENDIUM?
- Compendium is, as the name implies, a compilation style mod. Its main focus is not to include new levels (though some new content is included), but rather a hand picked compilation of some of the best doom mods and levelpacks released from 1994 to about 2004-2005. In its present form, the compilation has 52 mods included for a total of over 1000 levels. The mods have been preserved to be pretty much exactly the same as the original files as it is not my intention to change the authors' original vision, with a few changes mostly for technical reasons which I will explain below.

QUESTION #2: WHY DO THIS?
- There are multiple reasons why I chose to do this. The main reason is that, despite having been a ZDoom user pretty much ever since my entry into the doom community, I find that the types of wads I tend to enjoy the most are oldschool-style levels. It's not entirely straightforward to explain why I prefer them over other things, and this is also not the point of the question, but suffice to say they offer a style of gameplay and level design that I find to be largely lost in a lot of modern mappacks. Whether that's for better or worse varies depending on who you ask, but personally I think there is still a lot mappers can learn by playing these wads. The secondary reason I'm doing this is because Doom mods, despite the amazing service provided by the idgames database, remain somewhat poorly organized and documented to the uninitiated: some of these mods were still stuck with things like DOS installers, multiple files to load with confusing instructions and stuff like that. Some of these also ran into obvious limitations dictated by their reliance on DeHackEd (all DeHackEd code has been converted to DECORATE) or by fairly hacky features in the original engine which for example made it really difficult to ensure optimal multiplayer compatibility (see below for more information). Other communities, such as the Duke Nukem 3D forums, have made a similar compilation-style effort to the one I am doing so I figured it is time the Doom community had something along those lines not only as a convenience but also as a (hopefully) comprehensive look into the history of perhaps the greatest modding effort that has ever occurred for any videogame.

QUESTION #3: HOW DOES IT WORK EXACTLY?
- The mod, as noted, does not require you to load multiple files individually to play different maps. Instead, the single .pk3 which is provided here is all you need (alongside a copy of DOOM2.wad, obviously) to play. The way it is structured is, there's a central hub map upon starting a new game. This hub map will take you to a large landscape area which you can explore, and upon exploring you will come across several gateways. These gateways, as indicated by their logo, will take you to each of the mappacks. Before proceeding to the levels themselves you will enter a separate, small area beyond each gateway, and here you will learn what the wad you are about to play is like, how long it lasts, who made it and when, etc. This allows anyone to easily find something they'd be more comfortable playing if they are a fan of specific styles of gameplay or level design. Once in the mappack itself, it plays normally just like the originals, including having the appropriate intermission graphics and music. Upon completing the mappack you will be taken back to the hub map, where you will get to keep your arsenal and then play any other mappacks that you want. If you on the other hand want to start with an empty arsenal when starting a new one, all you have to do is start a new game and your inventory will be cleared.

QUESTION #4: WHAT PORTS IS THIS COMPATIBLE WITH?
- This mod has been tested almost exclusively with several versions of GZDoom, where it is guaranteed to work perfectly. It has also been tested in multiplayer Zandronum, but functionality there is less than ideal in part also because some of these wads are really not meant to be played online and there is little I can do to change that. In short, this mod is guaranteed to work under the latest versions of GZDoom and is NOT guaranteed to work anywhere else. Keep that in mind.

QUESTION #5: ISN'T PORTING ALL THIS TO GZDOOM MESSING WITH THE ORIGINAL GAME'S SPIRIT, THOUGH?
- Not really. I have never been one of those who think GZDoom for one reason or another ruins the original game's spirit or purpose, I simply think it removes a lot of limitations and adds a lot of new features that modders can take advantage of, but otherwise the core game remains largely the same, with most of the changes being purely technical. That being said, if you are one of those who think the mods must be experienced absolutely and exclusively in their original form and fashion with no changes even on a source port level, then this mod obviously isn't for you and what you should do instead is track down the original mod .wad files and play them through DOSBox or, even better, an actual DOS machine. For anyone else however, this mod should provide a convenient, comprehensive and complete package for experiencing the history of doom modding.

QUESTION #6: WHY ISN'T MY FAVORITE WAD HERE?
- First off, keep in mind that as noted this compilation focuses largely on the Doom modding scene of the 90s and early 2000s. As a result this won't contain anything recent. So, no Scythe 2, no BTSX, no Valiant, etc etc. That said however, it is impossible for me to include all wads, major and minor, in this. As a result some WADs from back in the day that are well known might be missing. While the criteria I used to establish what to include are a bit personal and I guess in a way arbitrary, I did try to include several WADs that espoused different gameplay and design philosophies to ensure the largest amount of variety possible. While this means that some WADs are generally universally appreciated, like the amazing Memento Mori series for example, some might only be truly enjoyed by a specific group of people. As a practical example, take Cleimos 2. It is very, very heavy on mazes. If that's your thing, you surely will enjoy it, but many others might want steer clear of that one in particular. Likewise, Scythe, with its super short maps and in-your-face action might not be much appreciated by those who prefer a long, puzzle-heavy adventure such as Eternal Doom.

QUESTION #7: IS THIS COMPATIBLE WITH GAMEPLAY MODS?
- Yes, this is compatible with gameplay mods, at least it has been compatible with those that I have tested (there could always be exceptions for particularly complex gameplay mods; I don't usually play many of them alas). Even so however, there still could be a few issues with some of the mods on here, for instance I'm not sure if something like Daedalus would work correctly with weapon mods (but if it doesn't then that applies to the original Daedalus files as well and is not a Compendium-related problem) as well as the fact that, for example, in my experience a few gameplay mods tend to break things like map07 vanilla scripts. In short, as far as the eye could see this should be fully compatible with gameplay mods, but if an issue presents itself you can let me know and if the mod's author is willing to look into it we can see if it is something that's easily fixable or not. The workload for this mod has been absolutely massive, so understand that I've had other priorities besides testing a lot of gameplay mods.

QUESTION #8: WHAT ARE THOSE CHANGES YOU SPOKE OF?
- This will be a fairly long explanation. I can summarize the changes by splitting them into five main categories which I will now list:

1) The first order of changes is, quite simply, bugfixes. While I do want to preserve the wads to be as true as possible to the originals, at the same time I am not happy when the maps have clearly unintended bugs which can for example allow you to get stuck and be unable to progress. These bugfixes are related both to single player and to multi player compatibility. For instance in Requiem MAP08, The Reactor, near the end of the level there is a small lift housing a chaingunner to ambush the player. It is actually possible to get on this lift but if you do get on it, there is no way out and you are stuck unless you cheat or reload an older save. A switch has now been added in that room to allow you to get off the lift and progress through the level normally. As far as multiplayer bugfixes go, an example would be BioWar MAP11, Frozen Terror. Near the start, you enter a room after which bars close down behind you preventing you from escaping, but also unintentionally preventing any player left behind from proceeding. I have modified this so that a teleporter is available after the bars close, allowing multiplayer to proceed smoothly without otherwise changing the level in any way or form.

2) The second order of changes can be best described not as things that have been added on top of the original files but rather things that have NOT been ported over from the original files. The most notable absence is that of any custom weapons the original mods might have had. I have decided, at least for the time being, not to include any of those custom weapons and instead stick to the vanilla arsenal. There are several reasons for this: the first one is that I have a fair bit of experience in coding custom enemies and decorations, but on the other hand I have never found it comfortable to work with custom weapons under DECORATE, so on top of the already massive workload that I had I really did not want to add that to the list. The second reason is that including any custom weapon creates a bit of a paradox in the case that you find a weapon in one mod, then you go play another mod using a weapon you're not meant to, such as using the Strain plasma rifle replacement, which even uses a different ammo type, in Memento Mori. The third reason is that adding any custom weapon might compromise compatibility with ZDoom gameplay mods which, while not that high on my priority list, is something I have managed to mantain nonetheless so I'd like to keep it until I can perhaps come up with a better system to implement all these.
Additional things that have been not included are things such as custom sound replacements for stuff like doors or vanilla weapons that some of the wads had: including these would not only be extremely impractical but also generally useless. There are also some things that I did not include, even though I really wanted to and I still am looking to implement workarounds, simply because GZDoom for one reason or another prevented me from doing so. The main thing I am unable to implement is Ghost Monsters, a vanilla doom bug/"feature" which GZDoom supports for specific WADs, but for some reason it does not let you add a flag on MAPINFO to allow you to have ghost monsters on your own custom levels, which doesn't make a whole lot of sense to me. So the only way I can get ghost monsters in this is by either creating new actors exclusively for them (which is fairly impractical), having GZDoom devs add exceptions to all the maps in this mod that make use of ghost monsters (which I find to be unlikely), or if by some stroke of luck they decide to finally allow mappers to simply add ghost monsters to their levels by using MAPINFO. I understand that they might have their perfectly valid technical reasons not to allow us to do that, but considering more and more wads are added to the internal GZDoom list which supports ghost monsters, there isn't much of a reason why this should be added on their side and not on modders' side. I'm not trying to make a political case here, just explaining the absence of a fairly critical feature in at least a few of the levels (Icarus map24 comes to mind). I will try to solve it one way or another as soon as the opportunity presents, but for now, it is what it is. That said, it should not influence the mod significantly aside for a few of the levels which are nonetheless still perfectly beatable and playable even without them.

3) The third order of changes is technical changes, namely things that have been upgraded or modified simply because they are way more stable and allow for more flexibility/cross-compatibility than what was present before. The main example would be the conversion of DeHackED code into DECORATE (and sometimes ACS), as already mentioned. Because of the underlying difference between these two modding systems it is not possible to directly convert from one to the other, instead I did my best into rewriting custom dehacked enemies from scratch to be as close as possible to the originals. I think I've done a fairly good job at it and in some cases it's basically impossible to tell the difference between the DeHackEd original and the DECORATE remake, but in some other cases there might be very minor differences that nonetheless shouldn't have any practical impact.
Other technical changes include the re-construction of some parts of certain levels by making use of GZDoom's features. This has happened for one of two reasons: either they were displaying incorrectly in the OpenGL renderer, or they were making multiplayer compatibility highly problematic. An example of the former would be the bridge in Requiem MAP13, Town of the Dead. In its original format, the game would display a HOM effect underneath the bridge which was obviously not intentional. The bridge has been remade with 3D floors in a way that ensures that not only it looks exactly the same as the original (but without the HOM) but also behaves the same: the difference is purely technical, as I said. An example of the latter case, when it comes to multiplayer compatibility, would be in Caverns of Darkness MAP08, The Pit. Near the start of the mission there is a bridge hovering over the initial room: this bridge is later activated upon entering an elevator, and while this works perfectly well under single player conditions, in multiplayer it had the side effect of completely blocking access to the elevator area to both players who had not yet reached it, and also to whoever respawned, making the map more often than not unbeatable. The bridge has been remade with bridge things meaning that it functions the same as before but can now be used without blocking the room it hovers in.

4) The fourth order of changes is things that are not present in the originals but that I have either changed or added for several reasons. This list is notably small but I can further split it into two categories:
The first would be some minor things I have changed for aesthetic purposes. For instance a few of the mappacks, such as Last Day on Earth or City of Doom, use a very similar but higher resolution and better looking sky texture. This change is MAPINFO related and not something that I changed in the levels themselves, and only a few mappacks are affected, I think for the better.
The second category is strictly related to a mod called Mars Doom. This exceptional but tragically unfinished mod was one of the most complex doom mods ever released back in 2001. However due to its heavy reliance on DeHackEd, as well as the fact that the only thing we have is an unfinished beta because the final product was never completed, it was both clearly buggy and unfinished in some aspects. For one thing, it completely lacked certain types of ammunition because they had to be sacrificed to create new DeHackEd actors. This, upon testing, reveals to have unintentionally caused a severe ammo shortage in some of the levels, so I did scatter around some additional shells, clips and rockets in some of the levels so that they can be beatable properly (hopefully even on a pistol start). The other change again related to this mod is the fact that it contained a placeholder level, MAP04 The Arena, which consisted of nothing but an empty room with an exit pillar and seven weak enemies. I have edited this level to make it more akin to a proper level in the spirit of what I think it was going to go for, as well as to add some more meat to a mod which at 10 levels is still over very quickly. The Arena is the only level I have edited significantly out of the 900+ levels that exist in this, and I've done so only because it was a placeholder level and not a proper one. I am sure you won't mind.
Some other changed things include spellchecking that I've done for some of the ZDoom mods. Project Slipgate, for example, in the scripts sometimes had fairly broken English, and I've corrected the grammar while keeping the original meaning of the sentences otherwise intact. I realize broken English is sometimes part of the charm, but bear with me here. :P

5) The last thing could technically fall into the fourth category but I feel it deserves specific mention here. There is one more thing I have changed from the originals, and that is the fact that I declared war on slow as molasses elevators. The main reason for this is multiplayer but to be fair it leads to a much better single player experience as well. Let me explain. In vanilla Doom, it is possible to create more complex elevators (as opposed to the traditional lifts used in the IWADS which are already quite fast), but said elevators, whether they are switch-bound or automated, are limited to the agonizingly slow speed of 8! It's easy to see why the original mappers used speed 8, and that is quite simply because in 99% of cases no other speed is available beyond 8. What this means is that in some of the maps, such as Requiem MAP08 or almost the entirety of ASDoom2, some of the levels stop being about Doom and instead start being about "Waiting for the elevator: the game". In multiplayer you can spend more time riding and waiting for those elevators than you would be actually playing the level itself. This is why I decided to change some of the elevators from speed 8 to either 16 or 32. It ultimately does not affect gameplay in any way beyond preventing the situation I described earlier, so I don't feel I am messing with the original authors' vision (and as I said, it's not like they had the option back then). This applies only to the worst offender elevators, and one-time only elevators remain on their original speed. For example, on Eternal MAP08, Woodhead, the initial slow elevator needs to be used only once, so it remains at its original speed.

With the exception of ghost monsters (which is largely out of my jurisdiction as I explained), I don't think any of the changes I listed here will have any impact whatsoever for most players, in fact if anything a lot of them would have an impact for the better. However I decided to list all these both for intellectual honesty and also because if you are one of those die-hard purists, then some of these changes might affect you. If you can't bear the thought of playing a mod with a slightly higher resolution sky or fixed broken English in scripts or slightly faster elevators to prevent standstill situations, well then, as I said what you should do is look up the original files and play on DOSBox. I'm afraid if what I described bothers you then I don't think you are ultimately the target audience. If on the other hand you feel something must be changed, either to revert back to how it was or to further improve it from the original but without compromising the spirit, if you think you have a good case feel free to let me know and I'll see about it.

QUESTION #9: THIS PROJECT IS REALLY BIG. ARE YOU SURE YOU FIXED ALL THE BUGS?
- Welllllllllll.... I have spent hours upon hours playing and testing this to ensure everything works as it is expected to, but of course, I don't realistically expect to be able to find every single bug in 1000+ levels, that's way too much for a single human being to be able to do. If you find any bugs in the maps you are more than welcome to let me know and I'll see if they can be fixed and if they can I'll do it immediately. Some bugs however I won't touch, for instance things like not all items being able to be picked up in Requiem MAP12, or some other Requiem map I forget now having the wrong key required for a specific door, making one of the keys completely useless to have. Bugs like that are not game breaking in any way and while oversights, changing them would mean for instance completely cutting ties with things like speedruns and whatnot, and I'd rather not to do that. Some other things I won't do is add multiplayer compatibility for mods such as Cyberdreams or Daedalus. Doing so would require spending months redesigning all of the maps and scripts, and that's not something I plan on ever doing. Play those in SP as they are meant to be played. On the other hand, some that previously were not at all compatible with multiplayer, such as Caverns of Darkness, now are, so there's that. :P

QUESTION #10: DO YOU PLAN TO ADD EVEN MORE TO THIS AND WORK ON IT FURTHER?
- To be honest, I have been working long and hard on this for months and months, and I've dedicated way more time to it than I should have both for real life and for my personal sanity :P I am just glad that I am finally able to release it after all this time. I do actually have plans for future extensions of this, including a whole new section called Shooting Gallery, but if and when that'll come remains to be seen. It also depends a bit on the reception this will get, if not enough people are interested then I'm not sure I want to further commit to something when I ultimately already achieved my original objective with this mod. No promises are made, but we'll see what the future holds...