DOOM Developers Kit/Doom_Developers_Kit_Vol1.iso/doom_i/text/doom13.spe

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From: [e-mail] (Hank Leukart)
Newsgroups: rec.games.computer.doom.announce,alt.games.doom.announce
Subject: ** The Unofficial DOOM Specs v1.3 **
Date: 18 Nov 1994 16:55:45 -0000
Organization: Case Western Reserve University, Cleveland, OH (USA)
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\\ . . . . . . .\\   //. . . . . . .\\   //. . . . . . .\\  \\. . .\\// . . //
||. . ._____. . .|| ||. . ._____. . .|| ||. . ._____. . .|| || . . .\/ . . .||
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|| . .||   ||. _-|| ||-_ .||   ||. . || || . .||   ||. _-|| ||-_.|\ . . . . ||
||. . ||   ||-'  || ||  `-||   || . .|| ||. . ||   ||-'  || ||  `|\_ . .|. .||
|| . _||   ||    || ||    ||   ||_ . || || . _||   ||    || ||   |\ `-_/| . ||
||_-' ||  .|/    || ||    \|.  || `-_|| ||_-' ||  .|/    || ||   | \  / |-_.||
||    ||_-'      || ||      `-_||    || ||    ||_-'      || ||   | \  / |  `||
||    `'         || ||         `'    || ||    `'         || ||   | \  / |   ||
||            .===' `===.         .==='.`===.         .===' /==. |  \/  |   ||
||         .=='   \_|-_ `===. .==='   _|_   `===. .===' _-|/   `==  \/  |   ||
||      .=='    _-'    `-_  `='    _-'   `-_    `='  _-'   `-_  /|  \/  |   ||
||   .=='    _-'          `-__\._-'         `-_./__-'         `' |. /|  |   ||
||.=='    _-'                                                     `' |  /==.||
=='    _-'         S         P         E         C         S          \/   `==
\   _-'                                                                `-_   /
 `''                                                                      ``'
                        Release v1.3 - April 13, 1994 EST
                 Written by: Matt Fell ([e-mail])
           Distributed by: Hank Leukart ([e-mail])
            "DOOM: Where hackers gnaw the bones left from the banquet
                 of data prepared by the mighty wizards of id."
           "The poets talk about love, but what I talk about is DOOM,
                  because in the end, DOOM is all that counts."
            - Alex Machine/George Stark/Stephen King, _The Dark Half_
-----------------------------------------------------------------------------

----------
DISCLAIMER
----------

        These specs are to aid in informing the public about the game DOOM,
by id Software.  In no way should this promote your killing yourself, killing
others, or killing in any other fashion.  Additionally, neither Hank Leukart
nor Matt Fell claim ANY responsibility regarding ANY illegal activity
concerning this file, or indirectly related to this file.  The information
contained in this file only reflects id Software indirectly, and questioning
id Software regarding any information in this file is not recommended.

----------------
COPYRIGHT NOTICE
----------------

This article is Copyright 1993, 1994 by Hank Leukart.  All rights reserved.
You are granted the following rights:

I.  To make copies of this work in original form, so long as
      (a) the copies are exact and complete;
      (b) the copies include the copyright notice and these paragraphs
          in their entirety;
      (c) the copies give obvious credit to the author, Matt Fell;
      (d) the copies are in electronic form.
II. To distribute this work, or copies made under the provisions
    above, so long as
      (a) this is the original work and not a derivative form;
      (b) you do not charge a fee for copying or for distribution;
      (c) you ensure that the distributed form includes the copyright
          notice, this paragraph, the disclaimer of warranty in
          their entirety and credit to the author;
      (d) the distributed form is not in an electronic magazine or
          within computer software (prior explicit permission may be
          obtained from Hank Leukart);
      (e) the distributed form is the NEWEST version of the article to
          the best of the knowledge of the distributor;
      (f) the distributed form is electronic.

        You may not distribute this work by any non-electronic media,
including but not limited to books, newsletters, magazines, manuals,
catalogs, and speech.  You may not distribute this work in electronic
magazines or within computer software without prior written explicit
permission.  These rights are temporary and revocable upon written, oral,
or other notice by Hank Leukart. This copyright notice shall be governed
by the laws of the state of Ohio.
        If you would like additional rights beyond those granted above,
write to the distributor at "[e-mail]" on the Internet.

------------------------------
INTRODUCTION FROM HANK LEUKART
------------------------------

        Here are the long awaited unofficial specs for DOOM.  These specs
should be used for creating add-on software for the game. I would like to
request that these specs be used in making utilities that ONLY work on the
registered version of DOOM.
        I did not write these specs.  I am handling the distribution so
Matt Fell is not bombarded with E-mail with requests for the specs, etc.
If you would like a copy of the specs, E-mail Hank Leukart at
"[e-mail]" on the Internet.  If you would like to ask
technical questions or give technical suggestions about the specs, please
write to Matt Fell at "[e-mail]".

        Literature also written/distributed by Hank Leukart:

        - The "Official" DOOM FAQ:  A comprehensive guide to DOOM
        - DOOM iNsAnItY: A humorous look at DOOM and its players

--------
CONTENTS
--------

[1] Author's Notes
        [1-1] id Software's Copyright
        [1-2] What's New in the 1.3 Specs
        [1-3] Acknowledgments
[2] Basics
[3] Directory Overview
[4] The Maps, The Levels
        [4-1] ExMy
        [4-2] THINGS
                [4-2-1] Thing Types
                [4-2-2] Thing Attributes
        [4-3] LINEDEFS
                [4-3-1] Linedef Attributes
                [4-3-2] Linedef Types
        [4-4] SIDEDEFS
        [4-5] VERTEXES
        [4-6] SEGS
        [4-7] SSECTORS
        [4-8] NODES
        [4-9] SECTORS
                [4-9-1] Special Sector Types
        [4-10] REJECT
        [4-11] BLOCKMAP
                [4-11-1] Automatically Generating the BLOCKMAP
[5] Pictures
        [5-1] Headers
        [5-2] Pointers
        [5-3] Pixel Data
[6] Floor and Ceiling Textures
        [6-1] Animated floors, see [8-4-1]
[7] Songs and Sounds
        [7-1] Songs
        [7-2] Sounds
[8] Some Important Non-Picture Resources
        [8-1] PLAYPAL
        [8-2] COLORMAP
        [8-3] DEMOs
        [8-4] TEXTURE1 and TEXTURE2
                [8-4-1] Animated Walls
        [8-5] PNAMES

---------------------------
CHAPTER [1]: Author's Notes
---------------------------

[1-1]: id Software's Copyright and the Shareware Version
========================================================

The LICENSE.DOC says:

       `You may not:  rent, lease, modify, translate, disassemble, decompile,
        reverse engineer, or create derivative works based upon the Software.
        Notwithstanding the foregoing, you may create a map editor, modify
        maps and make your own maps (collectively referenced as the "Permitted
        Derivative Works") for the Software. You may not sell or distribute
        any Permitted Derivative Works but you may exchange the Permitted
        Derivative Works at no charge amongst other end-users.'

       `(except for backup purposes) You may not otherwise reproduce, copy or
        disclose to others, in whole or in any part, the Software.'

        I think it is clear that you may not distribute a wad file that
contains any of the original data resources from DOOM.WAD. A level that only
has new things should be distributed as a pwad with only two entries in its
directory (explained below, in chapter [2]) - e.g. E3M1 and THINGS. And the
THINGS resource in the pwad should be substantially different from the
original one in DOOM.WAD. You should not distribute any pwad files that
contain episode one maps. Here's an excerpt from README.EXE:

       `id Software respectfully requests that you do not modify the levels
        for the shareware version of DOOM.  We feel that the distribution of
        new levels that work with the shareware version of DOOM will lessen a
        potential user's incentive to purchase the registered version.

       `If you would like to work with modified levels of DOOM, we encourage
        you to purchase the registered version of the game.'

        Recently, Jay Wilbur of id Software announced the formulation of a
policy on third-party additions to the game. You can find the announcement on
alt.games.doom, and probably lots of other places too. Or you can send me
mail asking for a copy of the announcement. Basically, they are preparing a
document, and if it was done, then I could tell you more, but it isn't
finished at the time I'm writing this.
        If you're making add-ons, plan on them not working on the shareware
game, and plan on including statements about the trademarks and copyrights
that id Software owns, as well as disclaimers that they won't support your
add-on product, nor will they support DOOM after it has been modified.

[1-2]: What's New in the 1.3 Specs
==================================

        The main reason for this release of the specs, 1.3, is of course the
explanation of the NODES structure. I've been delaying a little bit, because
I wanted to see if it would be feasible to include a good algorithm herein.
Also, I wanted to wait and see if someone could actually implement "node
theory" in a level editor, thereby verifying it.
        Now the theory HAS been verified. However, the actual implementation
is still being worked on (debugged) as I'm writing this. Also, I don't want
to steal anyone's hard work outright. This means that there is NOT a node
creation algorithm here, but I do outline how one can be done. I have tried
to come up with one on my own, but it is too difficult for me, especially
with all the other things I'm simultaneously doing.
        Where you WILL find pseudo-code is in the BLOCKMAP section. I
borrowed an excellent idea from a contributor, and code based on the
algorithm given here should be very fast. Even huge levels should
recalculate in seconds.
        Another new section completely explains the REJECT resource.
        This entire document has been re-formatted, and there have been
several other additions, and hopefully the last of the typos has been rooted
out. I consider these specs to be at least 95% complete. There are only minor
gaps in the information now. If the promised "official specifications" were
released today, I expect this would compare favorably with them (although
I know exactly what parts of it I would look to first).
        I've been notified of something very disappointing, and after a
couple weeks of trying there seems to be no way around it. The pictures that
are used for sprites (things like barrels, demons, and the player's pistol)
all have to be listed together in one .WAD file. This means that they don't
work from pwad files. The same thing goes for the floor pictures. Luckily,
the walls are done in a more flexible way, so they work in pwads. All this is
explained in chapter [5].

[1-3]: Acknowledgments
======================

        I have received much assistance from the following people. They
either brought mistakes to my attention, or provided additional information
that I've incorporated into these specs:

Ted Vessenes ([e-mail])
        I had the THING angles wrong in the original specs.
Matt Tagliaferri ([e-mail])
        The author of the DOOMVB40 editor (aka DOOMCAD). I forgot to describe
        the TEXTURE1/2 pointer table in the 1.1 specs. Also, helped with
        linedef types, and provided a good BLOCKMAP algorithm.
Raphael Quinet ([e-mail])
        The author of the NEWDEU editor, now DEU 5, the first editor that can
        actually do the nodes. Go get it. Gave me lots of rigorous
        contributions on linedef types and special sectors.
Robert Fenske ([e-mail])
        Part of the team that created the VERDA editor. Gave me a great list
        of the linedef attributes; also helped with linedef types, a blockmap
        list, special sectors, and general tips and suggestions.
John A. Matzen ([e-mail])
        Instrument names in GENMIDI.
Jeff Bird ([e-mail])
        Good ideas and suggestions about the NODES, and a blockmap algorithm.
Alistair Brown ([e-mail])
        Helped me understand the NODES; and told me how REJECT works.
Robert D. Potter ([e-mail])
        Good theory about what BLOCKMAP is for and how the engine uses it.
Joel Lucsy ([e-mail])
        Info on COLORMAP and PLAYPAL.
Tom Nettleship ([e-mail])
        I learned about BSP trees from his comp.graphics.algorithms messages.
Colin Reed ([e-mail])
        I had the x upper and lower bounds for node bounding boxes backwards.
Frans P. de Vries ([e-mail])
        Thanks for the cool ASCII DOOM logo used for the header.

        Thanks for all the help! Sorry if I left anyone out. If you have
any comments or questions, have spotted any errors, or have any possible
additions, please send me e-mail.

-------------------
CHAPTER [2]: Basics
-------------------

        There are two types of "wad" files. The original DOOM.WAD file is an
"IWAD", or "Internal wad", meaning it contains all of the data necessary to
play. The other type is the "PWAD" file, "Patch wad", an external file which
has the same structure, but with far fewer entries in the directory
(explained below). The data in a pwad is substituted for the original data in
the DOOM.WAD, thus allowing for much easier distribution of new levels. Only
those resources listed in the pwad's directory are changed, everything else
stays the same.
        A typical pwad might contain new data for a single level, in which
case in would contain the 11 entries necessary to define the level. Pwad
files need to have the extension .WAD, and the filename needs to be at least
four characters: X.WAD won't work, but rename it XMEN.WAD, and it will work.
Most of the levels available now are called something like E2L4BOB.WAD,
meaning episode 2, level 4, by "Bob". I think a better scheme is the one just
starting to be used now, two digits for the episode and level, then up to six
letters for the level's name, or its creator's name. For example, if Neil
Peart were to create a new level 6 for episode 3, he might call it
36NEILP.WAD.
        To use this level instead of the original e3m6 level, a player would
type DOOM -FILE 36NEILP.WAD at the command line, along with any other
parameters. More than one external file can be added at the same time, thus
in general:

DOOM -FILE [pwad_filename] [pwad_filename] [pwad_filename] ...

        When the game loads, a "modified game" message will appear if there
are any pwads involved, reminding the player that id Software will not give
technical support or answer questions regarding modified levels.
        A pwad file may contain more than one level or parts of levels, in
fact there is apparently no limit to how many entries may be in a pwad. The
original doom levels are pretty complicated, and they are from 50-200
kilobytes in size, uncompressed. Simple prototype levels are just a few k.
        The first twelve bytes of a wad file are as follows:

Bytes 0 to 3    must contain the ASCII letters "IWAD" or "PWAD"
Bytes 4 to 7    contain a long integer which is the number of entries in the
                "directory"
Bytes 8 to 11   contain a pointer to the first byte of the "directory"

        Bytes 12 to the start of the directory contain resource data. The
directory referred to is a list, located at the end of the wad file, which
contains the pointers, lengths, and names of all the resources in the wad
file. The resources in the wad include item pictures, monster's pictures for
animation, wall patches, floor and ceiling textures, songs, sound effects,
map data, and many others.
        As an example, the first 12 bytes of the DOOM.WAD file might be
"49 57 41 44 d4 05 00 00 c9 fd 6c 00" (in hexadecimal). This is "IWAD", then
5d4 hex (=1492 decimal) for the number of directory entries, then 6cfdc9 hex
(=7142857 decimal) for the first byte of the directory.
        Each directory entry is 16 bytes long, arranged this way:

First four bytes:       pointer to start of resource (a long integer)
Next four bytes:        length of resource (another long integer)
Last eight bytes:       name of resource, in ASCII letters, ending with
                        00s if less than eight bytes.

-------------------------------
CHAPTER [3]: Directory Overview
-------------------------------

        This is a list of most of the directory entries. It would take 2000
lines to list every single entry, and that would be silly. All the ST entries
are for status bar pictures, so why list every one? And the naming convention
for the 700 sprites is easy (see chapter [5]), so there's no need to list
them all individually.

PLAYPAL   contains fourteen 256 color palettes, used while playing Doom.
COLORMAP  maps colors in the palette down to darker ones, for areas of less
            than maximum brightness (quite a few of these places, huh?).
ENDOOM    is the text message displayed when you exit to DOS.
DEMOx     x=1-3, are the demos which will play if you just sit and watch.
E1M1      etc, to E3M9, along with its 10 subsequent entries, defines the
          map data for a single level or mission.
TEXTURE1  is a list of wall type names used in the SIDEDEF portion of each
            level , and their composition data, i.e. what wall patches make
            up each texture.
TEXTURE2  contains the walls that are only in the registered version.
PNAMES    is the list of wall patches, which are referenced by number in the
            TEXTURE1/2 resources.
GENMIDI   has the names of every General Midi standard instrument in order
            from 0-127. Anyone know more...?
DMXGUS    obviously has to do with Gravis Ultra Sound. It's a text file, easy
            to read. Just extract it (WadTool works nicely).
D_ExMy    is the music for episode x level y.
D_INTER   is the music played on the summary screen between levels.
D_INTRO   is the 4 second music played when the game starts.
D_INTROA  is also introductory music.
D_VICTOR  is the music played on the victory text-screen after an episode.
D_BUNNY   is music for while a certain rabbit has his story told...
DP_xxxxx  DP and DS come in pairs and are the sound effects. DP_ are the PC
DS_xxxxx    speaker sounds, DS_ are the sound card sounds.

        All the remaining entries in the directory, except the floor textures
at the end, and the "separators" like S_START, refer to resources which are
pictures, in the doom/wad picture format described in chapter [5]. The floor
textures are also pictures, but in a raw format described in chapter [6].
        The next seven are full screen (320 by 200 pixel) pictures:

HELP1     The ad-screen that says Register!, with some screen shots.
HELP2     The actual help, all the controls explained.
TITLEPIC  Maybe this is the title screen? Gee, I dunno...
CREDIT    The credits, the people at id Software who created this great game.
VICTORY2  The screen shown after a victorious end to episode 2.
PFUB1     A nice little rabbit minding his own peas and queues...
PFUB2     ...maybe a hint of what's waiting in Doom Commercial version.
ENDx      x=0-6, "THE END" text, with (x) bullet holes.
AMMNUMx   x=0-9, are the gray digits used in the status bar for ammo count.
STxxxxxx  are small pictures and text used on the status bar.
M_xxxxxx  are text messages (yes, in picture format) used in the menus.
BRDR_xxx  are tiny two pixel wide pictures use to frame the viewing window
            when it is not full screen.
WIxxxxxx  are pictures and messages used on the summary screen after
            the completion of a level.
WIMAPx    x=0-2, are the summary-screen maps used by each episode.
S_START   has 0 length and is right before the item/monster "sprite" section.
            See chapter [5] for the naming convention used here.
S_END     is immediately after the last sprite.
P_START   marks the beginning of the wall patches.
P1_START    before the first of the shareware wall patches.
P1_END      after the last of the shareware wall patches.
P2_START    before the first of the registered wall patches.
P2_END      before the first of the registered wall patches.
P_END     marks the end of the wall patches.
F_START   marks the beginning of the floors.
F1_START    before the first shareware floor texture.
F1_END      after the last shareware floor texture.
F2_START    before the first registered floor texture.
F2_END      after the last registered floor texture.
F_END     marks the end of the floors.

        And that's the end of the directory.

        It is possible to include other entries and resources in a wad file,
e.g. an entry called CLOWNS could point to a resource that includes the
level creator's name, date of completion, or a million other things. None of
these non-standard entries will be used by DOOM, nor will they cause it
problems. Some of the map editors currently out add extra entries. There is
a debate going on right now as to the merits of these extras. Since they are
all non-standard, and potentially confusing, for now I'm in favor of not
using any extra entries, and instead passing along a text file with a pwad.
However, I can see some possible advantages, and I might change my mind...

---------------------------------
CHAPTER [4]: The Maps, The Levels
---------------------------------

        Each level needs eleven resources/directory entries: E[x]M[y],
THINGS, LINEDEFS, SIDEDEFS, VERTEXES, SEGS, SSECTORS, NODES, SECTORS,
REJECT, and BLOCKMAP.
        In the DOOM.WAD file, all of these entries are present for every
level. In a pwad external file, they don't all need to be present. Whichever
entries are in a pwad will be substituted for the originals. For example, a
pwad with just two entries, E3M1 and THINGS, would use all the walls and such
from the original E3M1, but could have a completely different set of THINGS.
        A note on the coordinates: the coordinate system used for the
vertices and the heights of the sectors corresponds to pixels, for purposes of
texture- mapping. So a sector that's 128 high, or a multiple of 128, is pretty
typical, since many wall textures are 128 pixels high.

[4-1]: ExMy
===========

        x is a single digit 1-3 for the episode number and y is 1-9 for the
mission/level number.
        This is just the name resource for a (single) level, and has zero
length. It marks any map-data resources that follow it in the directory list
as being components of that level. The assignment of resources to this level
stops with either the next ExMy entry, or with a non-map entry like TEXTURE1.

[4-2]: THINGS
=============

        Each thing is ten bytes, consisting of five (integer) fields:

(1) X coordinate of thing
(2) Y coordinate of thing
(3) Angle the thing faces. On the automap, 0 is east, 90 is north, 180 is
    west, 270 is south. This value is only used for monsters, player
    starts, deathmatch random starts, and teleporter incoming spots.  Others
    look the same from all directions. Values are rounded to the nearest 45
    degree angle, so if the value is 80, it will actually face 90 - north.
(4) Type of thing, see next subsection, [4-2-1]
(5) Attributes of thing, see [4-2-2]

[4-2-1]: Thing Types
--------------------

        Bytes 6-7 of each thing are an integer which specifies its kind:

Dec/Hex The thing's number
Sprite  The sprite name associated with this thing. This is the first four
          letters of the directory entries that are pictures of this thing.
seq.    The sequence of frames displayed. "-" means it displays nothing.
          Unanimated things will have just an "a" here, e.g. a backpack's
          only sprite can be found in the wad under BPAKA0. Animated things
          will show the order that their frames are displayed (they cycle
          back after the last one). So the blue key uses BKEYA0 then BKEYB0,
          etc. The soulsphere uses SOULA0-SOULB0-C0-D0-C0-B0 then repeats.

          Thing 15, a dead player, is PLAYN0.
+       Monsters and players and barrels. They can be hurt, and they have
          a more complicated sprite arrangement. See chapter [5].
CAPITAL Monsters, counts toward the KILL ratio at the end of a level.
*       An obstacle, players and monsters can't move through it.
^       Hangs from the ceiling, or floats (if a monster).
$       A regular item that players may get.
!       An artifact item; counts toward the ITEM ratio at level's end.

Dec. Hex Sprite seq.    Thing is:

0    0000 ---- -        (nothing)
1    0001 PLAY +        Player 1 start (Player 1 start is needed even on)
2    0002 PLAY +        Player 2 start (levels intended for deathmatch only.)
3    0003 PLAY +        Player 3 start (Player starts 2-4 are only needed
for)
4    0004 PLAY +        Player 4 start (cooperative mode multiplayer games.)
5    0005 BKEY ab     $ Blue keycard
6    0006 YKEY ab     $ Yellow keycard
7    0007 SPID +      * SPIDER DEMON: giant walking brain boss
8    0008 BPAK a      $ Backpack
9    0009 SPOS +      * FORMER HUMAN SERGEANT: black armor shotgunners
10   000a PLAY w        Bloody mess (an exploded player)
11   000b ---- -        Deathmatch start positions. Must be at least 4/level.
12   000c PLAY w        Bloody mess, this thing is exactly the same as 10
13   000d RKEY ab     $ Red Keycard
14   000e ---- -        Marks the spot where a player (or monster) lands when
                        they teleport to the SECTOR that contains this thing.
15   000f PLAY n        Dead player
16   0010 CYBR +      * CYBER-DEMON: robo-boss, rocket launcher
17   0011 CELP a      $ Cell charge pack
18   0012 POSS a        Dead former human
19   0013 SPOS a        Dead former sergeant
20   0014 TROO a        Dead imp
21   0015 SARG a        Dead demon
22   0016 HEAD a        Dead cacodemon
23   0017 SKUL a        Dead lost soul, invisible (they blow up when killed)
24   0018 POL5 a        Pool of blood
25   0019 POL1 a      * Impaled human
26   001a POL6 ab     * Twitching impaled human
27   001b POL4 a      * Skull on a pole
28   001c POL2 a      * 5 skulls shish kebob
29   001d POL3 ab     * Pile of skulls and candles
30   001e COL1 a      * Tall green pillar
31   001f COL2 a      * Short green pillar
32   0020 COL3 a      * Tall red pillar
33   0021 COL4 a      * Short red pillar
34   0022 CAND a        Candle
35   0023 CBRA a      * Candelabra
36   0024 COL5 ab     * Short green pillar with beating heart
37   0025 COL6 a      * Short red pillar with skull
38   0026 RSKU ab     $ Red skullkey
39   0027 YSKU ab     $ Yellow skullkey
40   0028 BSKU ab     $ Blue skullkey
41   0029 CEYE abcb   * Eye in symbol
42   002a FSKU abc    * Flaming skull-rock
43   002b TRE1 a      * Gray tree
44   002c TBLU abcd   * Tall blue firestick
45   002d TGRE abcd   * Tall green firestick
46   002e TRED abcd   * Tall red firestick
47   002f SMIT a      * Small brown scrub
48   0030 ELEC a      * Tall, techno column
49   0031 GOR1 abcb   *^Hanging victim, swaying, legs gone
50   0032 GOR2 a      *^Hanging victim, arms out
51   0033 GOR3 a      *^Hanging victim, 1-legged
52   0034 GOR4 a      *^Hanging victim, upside-down, upper body gone
53   0035 GOR5 a      *^Hanging severed leg
54   0036 TRE2 a      * Large brown tree
55   0037 SMBT abcd   * Short blue firestick
56   0038 SMGT abcd   * Short green firestick
57   0039 SMRT abcd   * Short red firestick
58   003a SARG +      * SPECTRE: invisible version of the DEMON
59   003b GOR2 a       ^Hanging victim, arms out
60   003c GOR4 a       ^Hanging victim, upside-down, upper body gone
61   003d GOR3 a       ^Hanging victim, 1-legged
62   003e GOR5 a       ^Hanging severed leg
63   003f GOR1 abcb    ^Hanging victim, swaying, legs gone
2001 07d1 SHOT a      $ Shotgun
2002 07d2 MGUN a      $ Chaingun, gatling gun, mini-gun, whatever
2003 07d3 LAUN a      $ Rocket launcher
2004 07d4 PLAS a      $ Plasma gun
2005 07d5 CSAW a      $ Chainsaw
2006 07d6 BFUG a      $ BFG9000
2007 07d7 CLIP a      $ Ammo clip
2008 07d8 SHEL a      $ 4 shotgun shells
2010 07da ROCK a      $ 1 rocket
2011 07db STIM a      $ Stimpak
2012 07dc MEDI a      $ Medikit
2013 07dd SOUL abcdcb ! Soulsphere, Supercharge, +100% health
2014 07de BON1 abcdcb ! Health bonus
2015 07df BON2 abcdcb ! Armor bonus
2018 07e2 ARM1 ab     $ Green armor 100%
2019 07e3 ARM2 ab     $ Blue armor 200%
2022 07e6 PINV abcd   ! Invulnerability
2023 07e7 PSTR a      ! Berserk Strength
2024 07e8 PINS abcd   ! Invisibility
2025 07e9 SUIT a      ! Radiation suit
2026 07ea PMAP abcdcb ! Computer map
2028 07ec COLU a      * Floor lamp
2035 07f3 BAR1 ab+    * Barrel; blown up (BEXP sprite) no longer an obstacle.
2045 07fd PVIS ab     ! Lite goggles
2046 07fe BROK a      $ Box of Rockets
2047 07ff CELL a      $ Cell charge
2048 0800 AMMO a      $ Box of Ammo
2049 0801 SBOX a      $ Box of Shells
3001 0bb9 TROO +      * IMP: brown fireball hurlers
3002 0bba SARG +      * DEMON: pink bull-like chewers
3003 0bbb BOSS +      * BARON OF HELL: cloven hooved minotaur boss
3004 0bbc POSS +      * FORMER HUMAN: regular pistol shooting slimy human
3005 0bbd HEAD +      *^CACODEMON: red one-eyed floating heads. Behold...
3006 0bbe SKUL +      *^LOST SOUL: flying flaming skulls, they really bite

        I couldn't figure out a way to squeeze the following information into
the above table. RAD is the thing's radius, they're all circular for
collision purposes. HT is its height, for purposes of crushing ceilings and
testing if monsters or players are too tall to enter a sector. SPD is a
monster's speed. So now you know that a player is 56 units tall. Even though
this table implies that they're 16*2 wide, players can't enter a corridor
that's 32 wide. It must be at least 34 units wide (48 is the lowest width
divisible by 16). Although obstacles and monsters have heights, they are
infinitely tall for purposes of a player trying to go through them.

Dec. Hex   RAD   HT  SPD       Thing or class of things:

-       -   16   56    -       Player
7    0007  128  100   12       Spider-demon
9    0009   20   56    8       Former sergeant
16   0010   40  110   16       Cyber-demon
58   003a   30   56    8       Spectre
3001 0bb9   20   56    8       Imp
3002 0bba   30   56    8       Demon
3003 0bbb   24   64    8       Baron of Hell
3004 0bbc   20   56    8       Former human
3005 0bbd   31   56    8       Cacodemon
3006 0bbe   16   56    8       Lost soul
2035 07f3   10   42            barrel
            20   16            all gettable things
            16   16            most obstacles
54   0036   32   16            large brown tree

[4-2-2]: Thing attributes
-------------------------

        The last two bytes of a THING control a few attributes, according to
which bits are set:

bit 0   the THING is present at skill 1 and 2
bit 1   the THING is present at skill 3 (hurt me plenty)
bit 2   the THING is present at skill 4 and 5 (ultra-violence, nightmare)
bit 3   indicates a deaf guard.
bit 4   means the THING only appears in multiplayer mode.
bits 5-15 have no effect.

        The skill settings are most used with the monsters, of course...the
most common skill level settings are hex 07/0f (on all skills), 06/0e (on
skill 3-4-5), and 04/0c (only on skill 4-5).
        "deaf guard" only has meaning for monsters, who will not attack until
they see a player if they are deaf. Otherwise, they will activate when they
hear gunshots, etc (including the punch!). Sound does not travel through
solid walls (walls that are solid at the time of the noise). Also, lines can
be set so that sound does not pass through them (see [4-3-1] bit 6). This
attribute is also known as the "ambush" attribute.

[4-3]: LINEDEFS
===============

        Each linedef represents a line from one of the VERTEXES to another,
and each is 14 bytes, containing 7 (integer) fields:

(1) from the VERTEX with this number (the first vertex is 0).
(2) to the VERTEX with this number (31 is the 32nd vertex).
(3) attributes, see [4-3-1] below.
(4) types, see [4-3-2] below.
(5) is a "trigger" or "tag" number which ties this line's effect type to all
      SECTORS that have the same trigger number in their last field.
(6) "right" SIDEDEF, indexed number.
(7) "left" SIDEDEF, if this line adjoins 2 SECTORS. Otherwise, it is equal
      to -1 (FFFF hex).

        "right" and "left" are based on the direction of the linedef as
indicated by the "from" and "to" VERTEXES. This attempt at a sketch should
make it clear what I mean:

            left side              right side
    from -----------------> to <----------------- from
            right side             left side

        IMPORTANT: All lines must have a right side. If it is a one-sided
line, then it must go the proper direction, so its single side is facing
the sector it is part of.

[4-3-1]: Linedef Attributes
---------------------------

        The third field of each linedef is an integer which controls that
line's attributes with bits, as follows:

bit #  condition if it is set (=1)

bit 0   Impassable. Players and monsters cannot cross this line, and
          projectiles explode or end if they hit this line. Note, however,
          that if there is no sector on the other side, things can't go
          through this line anyway.
bit 1   Monster-blocker. Monsters cannot cross this line.
bit 2   Two-sided. If this bit is set, then the linedef's two sidedefs can
          have "-" as a texture, which means "transparent". If this bit is not
          set, the sidedefs can't be transparent: if "-" is viewed, it will
          result in the hall of mirrors effect. However, the linedef CAN have
          two non-transparent sidedefs, even if this bit is not set, if it is
          between two sectors.
        Another side effect of this bit is that if it is set, then
          projectiles and gunfire (pistol, etc.) can go through it if there
          is a sector on the other side, even if bit 0 is set.
        Also, monsters see through these lines, regardless of the line's
          other attribute settings and its textures ("-" or not doesn't matter).
bit 3   Upper texture is "unpegged". This is usually done at windows.
          "Pegged" textures move up and down when the neighbor sector moves
          up or down. For example, if a ceiling comes down, then a pegged
          texture on its side will move down with it so that it looks right.
          If the side isn't pegged, it just sits there, the new material is
          spontaneously created. The best way to get an idea of this is to
          change a linedef on an elevator or door, which are always pegged,
          and observe the result.
bit 4   Lower texture is unpegged.
bit 5   Secret. The automap will draw this line like a normal solid line that
          doesn't have anything on the other side, thus protecting the secret
          until it is opened. This bit is NOT what determines the SECRET
          ratio at the end of a level, that is done by special sectors (#9).
bit 6   Blocks sound. Sound cannot cross a line that has this bit set.
          Sound normally travels from sector to sector, so long as the floor
          and ceiling heights allow it (e.g. sound wouldn't go from a sector
          with 0/64 floor/ceiling height to one with 72/128, but sound WOULD
          go from a sector with 0/64 to one with 56/128).
bit 7   Not on map. The line is not shown on the regular automap, not even if
          the computer all-map power up is gained.
bit 8   Already on map. When the level is begun, this line is already on the
          automap, even though it hasn't been seen (in the display) yet.

bits 9-15 are unused, EXCEPT for a large section of e2m7, where every
wall on the border of the section has bits 9-15 set, so they have values like
1111111000000000 (-511) and 1111111000010000 (-495). This area of e2m7 is
also the only place in all 27 levels where there is a linedef 4 value of -1. But
the linedef isn't a switch. These unique values either do nothing, or
something that is as yet unknown. The currently prevailing opinion is that
they do nothing.
        Another rare value used in some of the linedef's attribute fields is
ZERO. It occurs only on one-sided walls, where it makes no difference whether
or not the impassibility bit (bit 0) is set. Still, it seems to indicate a
minor glitch in the DOOM-CAD editor (on the NExT), I suppose.

[4-3-2]: Linedef Types
----------------------

        The integers in field 4 of a linedef control various special effects,
mostly to do with what happens to a triggered SECTOR when the line is crossed
or activated by a player.
        Except for the ones marked DOOR, the end-level switches, and the
special type 48 (hex 30), all these effects need trigger/tag numbers. Then
any and all sectors whose last field contains the same trigger number are
affected when the linedef's function is activated.
        All functions are only performed from the RIGHT side of a linedef.
Thus switches and doors can only be activated from the right side, and
teleporter lines only work when crossed from the right side.
        What the letters in the ACT column mean:

W means the function happens when a player WALKS across the linedef.
S means a player must push SPACEBAR near the linedef to activate it (doors
    and switches).
G means a player or monster must shoot the linedef with a pistol or shotgun.
1 means it works once only.
R means it is a repeatable function.

        Some functions that appear to work only once can actually be made to
work again if the conditions are reset. E.g. a sector ceiling rises, opening
a little room with baddies in it. Usually, that's it. But perhaps if some
other linedef triggered that sector ceiling to come down again, then the
original trigger could make it go up, etc...
        Doors make a different noise when activated than the platform type
(floor lowers and rises), the ones that exhibit the door-noise are so called
in the EFFECT column. But only the ones marked DOOR in capitals don't need
trigger numbers.

Dec/Hex   ACT   EFFECT

-1 ffff   ? ?   None? Only once in whole game, on e2m7, (960,768)-(928,768)
0    00   - -   nothing
1    01   S R   DOOR. Sector on the other side of this line has its
                ceiling rise to 8 below the first neighbor ceiling on the
                way up, then comes back down after 6 seconds.
2    02   W 1   Open door (stays open)
3    03   W 1   Close door
5    05   W 1   Floor rises to match highest neighbor's floor height.
7    07   S 1   Staircase rises up from floor in appropriate sectors.
8    08   W 1   Stairs

Note: The stairs function requires special handling. An even number of steps
will be raised, starting with the first sector that has the same trigger
number as this linedef. Then the step sector's trigger number alternates
between 0 and any other value. The original maps use either 99 or 999, and
this is wise. The steps don't all have to start at the same altitude. All the
steps rise up 8, then all but the first rise another 8, etc. If a step hits
a ceiling, it stops. Some interesting effects are possible with steps that
aren't the same size or shape as previous steps, but in general, the most
reliable stairways will be just like the originals, congruent rectangles.

9    09   S 1   Floor lowers; neighbor sector's floor rises and changes
                TEXTURE and sector type to match surrounding neighbor.
10   0a   W 1   Floor lowers for 3 seconds, then rises
11   0b   S -   End level. Go to next level.
13   0d   W 1   Brightness goes to 255
14   0e   S 1   Floor rises to 64 above neighbor sector's floor
16   10   W 1   Close door for 30 seconds, then opens.
18   12   S 1   Floor rises to equal first neighbor floor
19   13   W 1   Floor lowers to equal neighboring sector's floor
20   14   S 1   Floor rises, texture and sector type change also.
21   15   S 1   Floor lowers to equal neighbor for 3 seconds, then rises back
                up to stop 8 below neighbor's ceiling height
22   16   W 1   Floor rises, texture and sector type change also
23   17   S 1   Floor lowers to match lowest neighbor sector
26   1a   S R   DOOR. Need blue key to open. Closes after 6 seconds.
27   1b   S R   DOOR. Yellow key.
28   1c   S R   DOOR. Red key.
29   1d   S 1   Open door, closes after 6 seconds
30   1e   W 1   Floor rises to 128 above neighbor's floor
31   1f   S 1   DOOR. Stays open.
32   20   S 1   DOOR. Blue key. Stays open.
33   21   S 1   DOOR. Yellow key. Stays open.
34   22   S 1   DOOR. Red key. Stays open.
35   23   W 1   Brightness goes to 0.
36   24   W 1   Floor lowers to 8 above next lowest neighbor
37   25   W 1   Floor lowers, change floor texture and sector type
38   26   W 1   Floor lowers to match neighbor
39   27   W 1   Teleport to sector. Only ONE sector can have the same tag #
40   28   W 1   Ceiling rises to match neighbor ceiling
41   29   S 1   Ceiling lowers to floor
42   2a   S R   Closes door
44   2c   W 1   Ceiling lowers to 8 above floor
46   2e   G 1   Opens door (stays open)
48   30   - -   Animated, horizontally scrolling wall.
51   33   S -   End level. Go to secret level 9.
52   34   W -   End level. Go to next level
56   38   W 1   Crushing floor rises to 8 below neighbor ceiling
58   3a   W 1   Floor rises 32
59   3b   W 1   Floor rises 8, texture and sector type change also
61   3d   S R   Opens door
62   3e   S R   Floor lowers for 3 seconds, then rises
63   3f   S R   Open door, closes after 6 seconds
70   46   S R   Sector floor drops quickly to 8 above neighbor
73   49   W R   Start crushing ceiling, slow crush but fast damage
74   4a   W R   Stops crushing ceiling
75   4b   W R   Close door
76   4c   W R   Close door for 30 seconds
77   4d   W R   Start crushing ceiling, fast crush but slow damage
80   50   W R   Brightness to maximum neighbor light level
82   52   W R   Floor lowers to equal neighbor
86   56   W R   Open door (stays open)
87   57   W R   Start moving floor (up/down every 5 seconds)
88   58   W R   Floor lowers quickly for 3 seconds, then rises
89   59   W R   Stops the up/down syndrome started by #87
90   5a   W R   Open door, closes after 6 seconds
91   5b   W R   Floor rises to 8 below neighbor ceiling
97   61   W R   Teleport to sector. Only ONE sector can have the same tag #
98   62   W R   Floor lowers to 8 above neighbor
102  66   S 1   Floor lowers to equal neighbor

103  67   S 1   Opens door (stays open)
104  68   W 1   Light drops to lowest light level amongst neighbor sectors

[4-4]: SIDEDEFS
===============

        A sidedef is a definition of what wall texture to draw along a
LINEDEF, and a group of sidedefs define a SECTOR.
        There will be one sidedef for a line that borders only one sector,
since it is not necessary to define what the doom player would see from the
other side of that line because the doom player can't go there. The doom
player can only go where there is a sector.
        Each sidedef is 30 bytes, comprising 2 (integer) fields, then 3
(8-byte string) fields, then a final (integer) field:

(1) X offset for pasting the appropriate wall texture onto the wall's
      "space": positive offset moves into the texture, so the left portion
      gets cut off (# of columns off left side = offset). Negative offset
      moves texture farther right, in the wall's space
(2) Y offset: analogous to the X, for vertical.
(3) "upper" texture name: the part above the juncture with a lower ceiling
      of an adjacent sector.
(4) "lower" texture name: the part below a juncture with a higher floored
      adjacent sector.
(5) "full" texture name: the regular part of the wall
(6) SECTOR that this sidedef faces or helps to surround

        The texture names are from the TEXTURE1/2 resources. 00s fill the
space after a wall name that is less than 8 characters. The names of wall
patches in the directory are not directly used, they are referenced through
the PNAMES.
        Simple sidedefs have no upper or lower texture, and so they will have
"-" instead of a texture name. Also, two-sided lines can be transparent, in
which case "-" means transparent (no texture).
        If the wall is wider than the texture to be pasted onto it, then the
texture is tiled horizontally. A 64-wide texture will be pasted at 0, 64,
128, etc. If the wall is taller than the texture, than the same thing is
done, it is vertically tiled, with one very important difference: it starts new
ones ONLY at 128, 256, 384, etc. So if the texture is less than 128 high,
there will be junk filling the undefined areas, and it looks ugly.

[4-5]: VERTEXES
===============

        These are the beginnings and ends for LINEDEFS and SEGS, each is 4
bytes, 2 (integer) fields:

(1) X coordinate
(2) Y coordinate

        On the automap within the game, with the grid on (press 'G'), the
lines are hex 80 (decimal 128) apart, two lines = hex 100, dec 256.

[4-6]: SEGS
===========

        The SEGS are in a sequential order determined by the SSECTORS, which
are part of the NODES recursive tree. Each seg is 12 bytes, having 6
(integer)
fields:

(1) from VERTEX with this number
(2) to VERTEX
(3) angle: 0= east, 16384=north, -16384=south, -32768=west.
      In hex, it's 0000=east, 4000=north, 8000=west, c000=south.
      This is also know as BAMS for Binary Angle Measurement.
(4) LINEDEF that this seg goes along
(5) 0 = this seg is on the right SIDEDEF of the linedef.
    1 = this seg is on the left SIDEDEF.
      This could also be thought of as direction: 0 if the seg goes the same
      direction as the linedef it's on, 1 if it goes the opposite direction.
(6) Offset distance along the linedef to the start of this seg (the vertex in
      field 1). The offset is in the same direction as the seg. If field 5 is
      0, then the distance is from the "from" vertex of the linedef to the
      "from" vertex of the seg. If feild 5 is 1, it is from the "to" vertex
of the linedef to the "from" vertex of the seg. So if the seg begins at
one of the two endpoints of the linedef, this will be 0.

        For diagonal segs, the offset distance can be obtained from the
formula DISTANCE = SQR((x2 - x1)^2 + (y2 - y1)^2). The angle can be
calculated from the inverse tangent of the dx and dy in the vertices, multiplied
to convert PI/2 radians (90 degrees) to 16384. And since most arctan functions
return a value between -(pi/2) and (pi/2), you'll have to do some tweaking
based on the sign of (x2-x1), to account for segs that go "west".

[4-7]: SSECTORS
===============

        SSECTOR stands for sub-sector. These divide up all the SECTORS into
convex polygons. They are then referenced through the NODES resources. There
will be (number of nodes) + 1 ssectors. Each ssector is 4 bytes, having 2
(integer) fields:

(1) This many SEGS are in this SSECTOR...
(2) ...starting with this SEG number

[4-8]: NODES
============

        The full explanation of the nodes follows this list of a node's
structure in the wad file. Each node is 28 bytes, composed of 14 (integer)
fields:

(1)  X coordinate of partition line's start
(2)  Y coordinate of partition line's start
(3)  DX, change in X to end of partition line
(4)  DY, change in Y to end of partition line
       64, 128, -64, -64 would be a partition line from (64,128) to (0,64)
(5)  Y upper bound for right bounding-box.\
(6)  Y lower bound                         All SEGS in right child of node
(7)  X lower bound                         must be within this box.
(8)  X upper bound                        /
(9)  Y upper bound for left bounding box. \
(10) Y lower bound                         All SEGS in left child of node
(11) X lower bound                         must be within this box.
(12) X upper bound                        /
(13) a NODE or SSECTOR number for the right child. If bit 15 is set, then the
       rest of the number represents the child SSECTOR. If not, the child is
       a recursed node.
(14) a NODE or SSECTOR number for the left child.

        The NODES resource is by far the most difficult to understand of all
the data structures in DOOM. A new level won't display right without a valid
set of precalculated nodes, ssectors, and segs. This is why so much time has
passed without a fully functional map-editor, even though many people are
working on them.
        Here I will explain what the nodes are for, and how they can be
generated automatically from the set of linedefs, sidedefs, and vertices. I
do NOT have a pseudo-code algorithm. There are many reasons for this. I'm not
actually programming a level editor myself, so I have no way of testing and
debugging a fully elaborated algorithm. Also, it is a very complicated
process, and heavily commented code would be very long. I'm not going to put
any language-specific code in here either, since it would be of limited
value. Finally, there are some implementations of automatic node generation
out there, but they are still being worked on, i.e. they still exhibit some
minot bugs.
        The NODES are branches in a binary space partition (BSP) that divides
up the level and is used to determine which walls are in front of others, a
process know as hidden-surface removal. The SSECTORS (sub-sectors) and SEGS
(segments) resources are necessary parts of the structure.
        A BSP tree is normally used in 3d space, but DOOM uses a simplified
2d version of the scheme. Basically, the idea is to keep dividing the map into
smaller spaces until each of the smallest spaces contains only wall segments
which cannot possibly occlude (block from view) other walls in its own space.
The smallest, undivided spaces will become SSECTORS. Each wall segment is
part or all of a linedef (and thus a straight line), and becomes a SEG. All
of the divisions are kept track of in a binary tree structure, which is used
to greatly speed the rendering process (drawing what is seen).
        Only the SECTORS need to be divided. The parts of the levels that are
"outside" sectors are ignored. Also, only the walls need to be kept track of.
The sides of any created ssectors which are not parts of linedefs do not
become segs.
        Some sectors do not require any dividing. Consider a square sector.
All the walls are orthogonal to the floor (the walls are all straight up and
down), so from any viewpoint inside the square, none of its four walls can
possibly block the view of any of the others. Now imagine a sector shaped
like this drawing:

+---------------.------+    The * is the viewpoint, looking ->, east. The
|                .     |    diagonal wall marked @ @ can't be seen at all,
|                /\    |@   and the vertical wall marked @@@ is partially
|   *->        /   @\  |@   occluded by the other diagonal wall. This sector
|            /       @\|@   needs to be divided. Suppose the diagonal wall
+----------/                is extended, as shown by the two dots (..):

now each of the two resulting sub-sectors are sufficient, because while in
either one, no wall that is part of that sub-sector blocks any other.
        In general, being a convex polygon is the goal of a ssector. Convex
means a line connecting any two points that are inside the polygon will be
completely contained in the polygon. All triangles and rectangles are convex,
but not all quadrilaterals. In doom's simple Euclidean space, convex also
means that all the interior angles of the polygon are <= 180 degrees.
        Now, an additional complication arises because of the two-sided
linedef. Its two sides are in different sectors, so they will end up in
different ssectors too. Thus every two-sided linedef becomes two segs (or
more), or you could say that every sidedef becomes a seg. Creating segs from
sidedefs is a good idea, because the seg can then be associated with a
sector.  Two segs that aren't part of the same sector cannot possibly be in
the same ssector, so further division is required of any set of segs that
aren't all from the same sector.
        Whenever a division needs to be made, a SEG is picked, somewhat
arbitrarily, which along with its imaginary extensions, forms a "knife" that
divides the remaining space in two (thus binary). This seg is the partition
line of a node, and the remaining spaces on either side of the partition line
become the right and left CHILDREN of the node. All partition lines have a
direction, and the space on the "right" side of the partition is the right
child of the node; the space on the "left" is the left child (there's a cute
sketch in [4-3]: LINEDEFS that shows how right and left relate to the start
and end of a line). Note that if there does not exist a seg in the remaining
space which can serve as a partition line, then there is no need for a
further partition, i.e. it's a ssector and a "leaf" on the node tree.
        If the "knife" passes through any lines/segs (but not at vertices),
they are split at the intersection, with one part going to each child. A two
sided linedef, which is two segs, when split results in four segs. A two
sider that lies along an extension of the partition line has each of its two
segs go to opposite sides of the partition line. This is the eventual fate of
ALL segs on two-sided linedefs.
        As the partition lines are picked and the nodes created, a strict
ordering must be maintained. The node tree is created from the "top" down.
After the first division is made, then the left child is divided, then its
left child, and so on, until a node's child is a ssector. Then you move back
up the tree one branch, and divide the right child, then its left, etc.
ALWAYS left first, on the way down.
        Since there will be splits along the way, there is no way to know
ahead of time how many nodes and ssectors there will be at the end. And the
top of the tree, the node that is created first, is given the highest number.
So as nodes and ssectors are created, they are simply numbered in order from
0 on up, and when it's all done, nothing's left but ssectors, then ALL the
numbers, for nodes and ssectors, are reversed. If there's 485 nodes, then 485
becomes 0 and 0 becomes 485.
        Here is another fabulous drawing which will explain everything. + is
a vertex, - and | indicate linedefs, the . . indicates an extension of a
partition line. The <, >, and ^ symbols indicate the directions of partition
lines. All the space within the drawing is actual level space, i.e. sectors.

      +-----+-------+-------+            0                     (5)
      |     |       |       |         /     \      ==>       /     \
      |  e  |^  f   |^  g   |       1         4           (4)       (1)
      |     |4      |5      |     /   \      / \         /   \      / \
+---- + . . +-------+-------+    2     3    e   5      (3)   (2)   2  (0)
|     |           < 0       |   / \   / \      / \     / \   / \      / \
|  a  |       b             |  a   b c   d    f   g   6   5 4   3    1   0
|     |^                    |
| . . |2. . . . . +---------+ The order in which      How the elements are
|     |           |1 >        the node tree's         numbered when it's
|  c  |^    d     |           elements get made.      finished.
|     |3          |           0 = node, a = ssector   (5) = node, 6 = ssector
+-----+-----------+

        1. Make segs from all the linedefs. There are 5 two-sided lines here.
        2. Pick the vertex at 0 and go west (left). This is the first
        partition line. Note the . . extension line.
        3. Pick the vertex at 1, going east. The backwards extension . . cuts
        the line 3>2>, and the unlabeled left edge line. The left edge was
        one seg, it becomes two. The 3>2> line was two segs, it becomes four.
        New vertices are created at the intersection points to do this.
        4. Pick the (newly created) vertex at 2. Now the REMAINING spaces on
        both sides of the partition line are suitable for ssectors. The left
        one is first, it becomes a, the right b. Note that ssector a has 3
        segs, and ssector b has 5 segs. The . . imaginary lines are NOT segs.
        5. Back up the tree, and take 1's right branch. Pick 3. Once again,
        we can make 2 ssectors, c and d, 3 segs each. Back up the tree to 0.
        6. Pick 4. Now the left side is a ssector, it becomes e. But the
        right side is not, it needs one more node. Pick 5, make f and g.
        7. All done, so reverse all the ordination of the nodes and the
        ssectors. Ssector 0's segs become segs 0-2, ssector 1's segs become
        segs 3-7, etc. The segs are written sequentially according to the
        ssector numbering.

        If we want to create an algorithm to do the nodes automatically, it
needs to be able to pick partition lines automatically. From studying the
original maps, it appears that they usually choose a linedef which divides
the child's space roughly in "half". This is restricted by the availability of
a seg in a good location, with a good angle. Also, the "half" refers to the
total number of ssectors in any particular child, which we have no way of
knowing when we start! Optimization methods are probably used, or maybe brute
force, trying every candidate seg until the "best" one is found.
        What is the best possible choice for a partition line? Well, there
are apparently two goals when creating a BSP tree, which are partially
exclusive. One is to have a balanced tree, i.e. for any node, there are about
the same total number of sub-nodes on either side of it. The other goal is to
minimize the number of "splits" necessary, in this case, the number of seg
splits needed, along with the accompanying new vertexes and extra segs. Only
a very primitive and specially constructed set of linedefs could avoid having
any splits, so they are inevitable. It's just that with some choices of
partition lines, there end up being fewer splits. For example,

+--------------+       If a and b are chosen as partition lines, there will
|              |       be four extra vertices needed, and this shape becomes
+---+      +---+ < A   five ssectors and 16 segs. If A and B are chosen,
    |^    ^|           however, there are no extra vertices, and only three
+---+a    b+---+ < B   ssectors and 12 segs.
|              |
+--------------+

        I've read that for a "small" number of polygons (less than 1000?),
which is what we're dealing with in a doom level, one should definitely try
to minimize splits, and not worry about balancing the tree. I can't say for
sure, but it does appear that the original levels strive for this. Their
trees are not totally unbalanced, but there are some parts where many successive
nodes each have a node and a ssector as children (this is unbalanced). And
there are a lot of examples to prove that the number of extra segs and
vertices they create is very low compared to what it could be. I think the
algorithm that id Software used tried to optimize both, but with fewer splits
being more important.

[4-9]: SECTORS
==============

        A SECTOR is a horizontal (east-west and north-south) area of the map
where a floor height and ceiling height is defined. It can have any shape.
Any change in floor or ceiling height or texture requires a new sector (and
therefore separating linedefs and sidedefs).
        Each is 26 bytes, comprising 2 (integer) fields, then 2 (8-byte
string) fields, then 3 (integer) fields:

(1) Floor is at this height for this sector
(2) Ceiling height
      A difference of 24 between the floor heights of two adjacent sectors
      is passable (upwards), but a difference of 25 is "too high". The player
      may fall any amount.
(3) name of floor texture, from the directory.
(4) name of ceiling texture, from directory.
      All the pictures in the directory between F_START and F_END work as
      either floors or ceilings. F_SKY1 is used as a ceiling to indicate that
      it is transparent to the sky above/behind.
(5) brightness of this sector: 0 = total dark, 255 (ff) = maximum light
(6) special sector: see [4-9-1] immediately below.
(7) is a "trigger" number corresponding to a certain LINEDEF with the same
      trigger number. When that linedef is crossed, something happens to this
      sector - it goes up or down, etc...

[4-9-1]: Special Sector Types
-----------------------------

        These numbers control the way the lighting changes, and whether or
not a player gets hurt while standing in the sector. -10/20% means that the
player takes 20% damage at the end of every second that they are in the
sector, except at skill 1, they take 10% damage. If the player has armor,
then the damage is split between health and armor.
        For all the lighting effects, the brightness levels alternates
between the value given for this sector, and the lowest value amongst all the
sector's neighbors. Neighbor means a linedef has a side in each sector. If no
neighbor sector has a lower light value, then there is no lighting effect.
"blink off" means the light goes to the lower value for just a moment. "blink
on" means the light is usually at the neighbor value, then jumps up to the
normal value for a moment. "oscillate" means that the light level goes
smoothly from one value to the other; it takes about 2 seconds to go from
maximum to minimum and back (255 to 0 to 255).

Dec Hex Condition or effect

0   00  is normal, no special characteristic.
1   01  light blinks off at random times.
2   02  light blinks on every 0.5 second
3   03  light blinks on every 1.0 second
4   04  -10/20% health AND light blinks on every 0.5 second
5   05  -5/10% health
7   07  -2/5% health, this is the usual NUKAGE acid-floor.
8   08  light oscillates
9   09  SECRET: player must move into this sector to get credit for finding
        this secret. Counts toward the ratio at the end of the level.
10  0a  ?, ceiling comes down 30 seconds after level is begun
11  0b  -10/20% health. When player's HEALTH <= 10%, then the level ends. If
        it is a level 8, then the episode ends.
12  0c  light blinks on every 1.0 second
13  0d  light blinks on every 0.5 second
14  0e  ??? Seems to do nothing
16  10  -10/20% health

        All other values cause an error and exit to DOS.

[4-10]: REJECT
==============

        The REJECT resource is optional. Its purpose in the original maps is
to help speed the process of calculating when monsters detect the player(s).
It can also be used for some special effects.
        The size of a REJECT in bytes is (number of SECTORS ^ 2) / 8, rounded
up. It is an array of bits, with each bit controlling whether monsters in a
given sector can detect players in another sector.
        Make a table of sectors vs. sectors, like this:

         sector that the player is in
              0  1  2  3  4
            +---------------
sector    0 | 0  1  0  0  0
that      1 | 1  0  1  1  0
the       2 | 0  1  0  1  0
monster   3 | 0  1  1  1  0
is in     4 | 0  0  1  0  0

        A 1 means the monster cannot become activated by seeing a player, nor
can it attack the player. A 0 means there is no restriction. All non-deaf
monsters still become activated by weapon sounds that they hear (including
the bare fist!). And activated monsters will still pursue the player, but they
will not attack if their current sector vs. sector bit is "1". So a REJECT
that's set to all 1s gives a bunch of pacifist monsters who will follow the
player around and look menacing, but never actually attack.
        How the table turns into the REJECT resource:
        Reading left-to-right, then top-to-bottom, like a page, the first bit
in the table becomes bit 0 of byte 0, the 2nd bit is bit 1 of byte 0, the 9th
bit is bit 0 of byte 1, etc. So if the above table represented a level with
only 5 sectors, its REJECT would be 4 bytes:

10100010 00101001 01000111 xxxxxxx0 (hex A2 29 47 00, decimal 162 41 71 0)

        In other words, the REJECT is a long string of bits which are read
from least significant bit to most significant bit, according to the
multi-byte storage scheme used in a certain "x86" family of CPUs.
        Usually, if a monster in sector A can't detect a player in sector B,
then the reverse is true too, thus if 0/1 is set, 1/0 will be set also. Same
sector prohibitions, e.g. 0/0, 3/3, etc. are very rarely set, only in tiny
sectors that monsters can't get to anyway. If a large sector with monsters
in it has this assignment, they'll exhibit the pacifist syndrome.
        I think the array was designed to help speed the monster-detection
process. If a sector pair is prohibited, the game engine doesn't even bother
checking line-of-sight feasibility for the monster to "see" the player and
thus become active. I suppose it can save some calculations if there are lots
of monsters.
        It is possible to automatically generate some reject pairs, but to
calculate whether or not one sector can "see" another can be very complicated.
You can't judge line-of-sight just by the two dimensions of the map, you also
have to account for the floor and ceiling heights. And to verify that every
point in the 3d volume of one sector is out of sight of every point in the
other sector...whew! The easy way is to just leave them all 0, or have a user
interface which allows them to use their brains to determine which reject
pairs should be set.

[4-11]: BLOCKMAP
================

        The BLOCKMAP is a pre-calculated structure that the game engine uses
to simplify collision-detection between moving things and walls. Below I'll
give a pseudo-code algorithm that will automatically construct a blockmap
from the set of LINEDEFS and their vertices.
        If a level doesn't have a blockmap, it can display fine, but
everybody walks through walls, and no one can hurt anyone else.
        The whole level is cut into "blocks", each is a 128 (hex 80) wide
square (the grid lines in the automap correspond to these blocks).
        All of the blockmap's fields are integers.
        The first two integers are XORIGIN and YORIGIN, which specify the
coordinates of the bottom-left corner of the bottom-left (southwest) block.
These two numbers are usually equal to 8 less than the minimum values of x
and y achieved in any vertex on the level.
        Then come COLUMNS and ROWS, which specify how many "blocks" there are
in the X and Y directions. COLUMNS is the number of blocks in the x
direction.
        For a normal level, the number of blocks must be large enough to contain
every linedef on the level. If there are linedefs outside the blockmap, they
will not be able to prevent monsters or players from crossing them, which can
cause problems, including the hall of mirrors effect.
        Then come (ROWS * COLUMNS) integers which are pointers to the offset
within the blockmap resource for that "block". These "offsets" refer to the
INTEGER number, NOT the byte number, where to find the block's list. The
blocks go right (east) and then up (north). The first block is at row 0,
column 0; the next at row 0, column 1; if there are 34 columns, the 35th
block is row 1, column 0, etc.
        After all the pointers, come the block lists. Each blocklist
describes the numbers of all the LINEDEFS which are partially or wholly "in"
that block. Note that lines and points which seem to be on the "border"
between two blocks are actually only in one. For example, if the origin of
the blockmap is at (0,0), the first column is from 0 to 127 inclusive, the
second column is from 128 to 255 inclusive, etc. So a vertical line with x
coordinate 128 which might seem to be on the border is actually in the
easternmost/rightmost column only. Likewise for the rows - the north/upper
rows contain the border lines.
        An "empty" block's blocklist consists of two integers: 0 and then -1.
A non-empty block will go something like: 0 330 331 333 -1. This means that
linedefs 330, 331, and 333 are "in" that block. Part of each of those line
segments lies within the (hex 80 by 80) boundaries of that block. What about
the block that has linedef 0? It goes: 0 0 ... etc ... -1.
        Here's another way of describing blockmap as a list of the integers,
in order:

        Coordinate of block-grid X origin
        Coordinate of block-grid Y origin
        # of columns (blocks in X direction)
        # of rows (blocks in Y direction)
        Block 0 offset from start of BLOCKMAP, in integers
          .
          .
        Block N-1 offset (N = number of columns * number of rows)
        Block 0 list: 0, numbers of every LINEDEF in block 0, -1 (ffff)
          .
          .
        Block N-1 list: 0, numbers of every LINEDEF in block N-1, -1 (ffff)

[4-11-1]: How to automatically generate the BLOCKMAP
----------------------------------------------------

        Here is an algorithm that can create a blockmap from the set of
linedefs and their vertices' coordinates. For reasons of space and different
programming tastes, I won't include every little detail here, nor is the
algorithm in any particular language. The pseudocode below is like BASIC or
PASCAL, sort of. I'm not being very formal about variable declarations and
such, since that's such a pain.
        There are basically two ways that the blockmap can be automatically
generated. The slow way is to do every block in order, and check every
linedef to see if part of the linedef is in the block. This method is slow
because it has to perform (number of blocks) * (number of linedefs)
iterations, and in most iterations it will have to do at least one fairly
complicated formula do determine an intersection. With the number of blocks
at 500-2500 for a typical level, and linedefs at 500-1500, this can really
bog down on a big level.
        The better way is to do the linedefs in order, keeping a dynamic list
for every block, and adding the linedef number to the end of the blocklist
for every block it passes through. We won't have to test every block to see if
the line passes through it; in fact, we won't be testing ANY blocks, we'll be
calculating exactly which blocks it goes through based on its coordinates and
slope. This method will have to go through one cycle for each linedef, with
very few calculations needed for most cycles, since most linedefs are in only
one or two blocks.

' Pseudo-code algorithm to generate a BLOCKMAP. The goal is speed. If you
' can top this approach, I'd be surprised.
' Most variables are of type integer, except slope and its pals, see below.
' Some of the ideas here are borrowed from Matt Tagliaferri.
' x_minimum is the minimum x value in the set of vertices, etc.
' the -8 is to make the blockmaps just like the original ones.

  x_origin = -8 + x_minimum
  y_origin = -8 + y_minimum
  Columns = ((x_maximum - x_origin) DIV 128) + 1
  Rows = ((y_maximum - y_origin) DIV 128) + 1

' DIV is whatever function performs integer division, e.g. 15 DIV 4 is 3.

  number_of_blocks = Rows * Columns
  INITIALIZE Block_string(number_of_blocks - 1)
  FOR count = 0 to number_of_blocks DO
    Block_string(count) = STRING(0)
  NEXT count

' STRING is whatever function or typecast will change the integer "int"
' to its two-byte string format. Here we set up an array to hold all the
' blocklists. All blocklists start with the integer 0, and end with -1;
' we'll add the -1s at the end.
' A string array is best, because we need to haphazardly add to the
' blocklists. line 0 might be in blocks 34, 155, and 276, for instance.
' And string's lengths are easily determined, which we'll need at the end.
' To save on memory requirements, the size of each array element can be
' limited to c. 200 bytes = 100 integers, since what is the maximum number
' of linedefs which will be in a single block? Certainly less than 100.

  FOR line = 0 TO Number_Of_Linedefs DO
    x0 = (x coordinate of that linedef's vertex 0) - x_origin
    y0 = (y coordinate of vertex 0) - y_origin
    x1 = (x coordinate of vertex 1) - x_origin
    y1 = (y coordinate of vertex 1) - y_origin

' subtracting the origins shifts the axes and makes calculations simpler.

    blocknum = (y0 DIV 128) * COLUMNS + (x0 DIV 128)
    Block_string(blocknum) = Block_string(blocknum) + STRING(line)

    boolean_column = ((x0 DIV 128)=(x1 DIV 128))
    boolean_row = ((y0 DIV 128)=(y1 DIV 128))

' This is meant to assign boolean values for whether or not the linedef's
' two vertices are in the same column and/or row. I'm assuming that the
' expressions will be evaluated as 1 if "true" and 0 if "false".
' So if both vertices are in the same block, both of these booleans will be
' true and we can go to the next linedef, because it's only in one block.
' If a line is horizontal or vertical, it is easy to calculate exactly which
' blocks it occupies. Since many, if not most, lines are orthogonal and
' short, that is where this algorithm gets most of its speed.

    CASE (boolean_column * 2 + boolean_row):
      CASE 3: NEXT line
      CASE 2: block_step = SIGN(y1-y0) * Columns
              FOR count = 1 TO ABS((y1 DIV 128) - (y0 DIV 128)) DO
                blocknum = blocknum + block_step
                Block_string(blocknum) = Block_string(blocknum) +
STRING(line)
              NEXT count
              NEXT line
      CASE 1: block_step = SIGN(x1-x0)
              count = 1 TO ABS((x1 DIV 128) - (x0 DIV 128)) DO
                blocknum = blocknum + block_step
                Block_string(blocknum) = Block_string(blocknum) +
STRING(line)
              NEXT count
              NEXT line
    END CASE

' now to take care of the longer, diagonal lines...

    y_sign = SIGN(y1-y0)
    x_sign = SIGN(x1-x0)

' Important: the variables "slope", "x_jump", "next_x" and "this_x" need to
' be of type REAL, not integer, to maintain the accuracy. "slope" will not
' be 0 or undefined, these situations were weeded out by CASE 1 and 2 above.
' An alternative was pointed out to me, but I haven't implemented it in this
' algorithm. If you scale these numbers by 1000, then 32 bit integer
' arithmetic will be precise enough, you won't need sloppy and slow real #s.

    slope = (y1-y0)/(x1-x0)
    x_jump = (128/slope) * y_sign
    CASE (y_sign):
      CASE -1: next_x = x0 + ((y0 DIV 128) * 128 - 1 - y0)/slope
      CASE 1: next_x = x0 + ((y0 DIV 128) * 128 + 128 - y0)/slope
    END CASE

' Suppose the linedef heads northeast from its start to its end. We'll
' first calculate all the blocks in the start row, which will all be
' successively to the right of the first block (blocknum). Then we'll move
' up to the next row, set the block, and go right, then the next row, etc.
' until we've passed the second/end vertex. (the three other directions
' NW SE SW are taken care of too, all by proper use of sign)

' x_jump is how far x goes right or left when y goes up/down 128.
' next_x will be the x coordinate of the next intercept with a "critical"
' y value. When the line goes up, the critical values are equal to 128, 256,
' etc, the first y-values in a new block. If the line goes down, then the
' intercepts occur when y equals 255, 127, etc. Remember, all this is in the
' "shifted" coord system.

' INT is whatever function will discard the decimal part of a real number,
' converting it to an integer. It doesn't matter which way it rounds
' negatives, since next_x and this_x are always positive.

    last_block = INT(next_x/128) - (x0 DIV 128) + blocknum
    IF last_block > blocknum THEN
      FOR count = (blocknum + x_sign) TO last_block STEP x_sign DO
        Block_string(count) = Block_string(count) + STRING(line)
      NEXT count

    REPEAT
      this_x = next_x

      next_x = this_x + x_jump
      IF (x_sign * next_x) > (x_sign * x1) THEN next_x = x1
      first_block = last_block + y_sign * Columns
      last_block = first_block + INT(next_x/128) - INT(this_x/128)
      FOR count = first_block TO last_block STEP x_sign DO
        Block_string(count) = Block_string(count) + STRING(line)
      NEXT count
    UNTIL INT(next_x) = x1


  NEXT line

' That's it. Now all we have to do is write the BLOCKMAP to wherever.

  WRITE Blockmap, AT OFFSET 0, x_origin
  WRITE Blockmap, AT OFFSET 2, y_origin
  WRITE Blockmap, AT OFFSET 4, Columns
  WRITE Blockmap, AT OFFSET 6, Rows

  pointer_offset = 8
  blocklist_offset = 8 + 2 * number_of_blocks
  FOR count = 0 TO number_of_blocks - 1 DO
     WRITE Blockmap, AT OFFSET pointer_offset, blocklist_offset / 2
     WRITE Blockmap, AT OFFSET blocklist_offset, Block_string(count)
     blocklist_offset = blocklist_offset + LENGTH(Block_string(count)) + 2
     WRITE Blockmap, AT OFFSET (blocklist_offset - 2), STRING(-1)
     pointer_offset = pointer_offset + 2
  NEXT count

' Done! blocklist_offset will equal the total size of the BLOCKMAP, when
' this last loop is finished

----------------------------
CHAPTER [5]: Pictures' Format
-----------------------------

        The great majority of the entries if the directory reference
resources that are in a special picture format. The same format is used for
the sprites (monsters, items), the wall patches, and various miscellaneous
pictures for the status bar, menu text, inter-level map, etc. The floor and
ceiling textures are NOT in this format, they are raw data; see chapter [6].
        After much experimenting, it seems that sprites and floors cannot be
added or replaced via pwad files. However, wall patches can (whew!). This is
apparently because all the sprites' entries must be in one "lump", in the
IWAD file, between the S_START and S_END entries. And all the floors have to
be listed between F_START and F_END. If you use those entries in pwads,
either nothing will happen, or an error will occur. There are also P_START
and P_END entries in the directory, which flank the wall patch names, so how
come they work in pwads? I think it is somehow because of the PNAMES
resource, which lists all the wall patch names that are to be used. Too bad
there aren't SNAMES and FNAMES resources!
        It is still possible to change and manipulate the sprites and floors,
its just more difficult to do, and very difficult to figure out a scheme for
potential distribution of changes. The DOOM.WAD file must be changed, and
that is a pain.
        All the sprites follow a naming scheme. The first four letters are
the sprite's name, or and abbreviation. TROO is for imps, BKEY is for the
blue key, etc. See [4-2-1] for a list of them.
        For most things, the unanimated ones, the next two characters of the
sprite's name are A0, like SUITA0, the radiation suit. For simple animated
things, there will be a few more sprites, e.g. PINVA0, PINVB0, PINVC0, and
PINVD0 are the four sprites for the Invulnerability power-up. Monsters are
the most complicated. They have several different sequences, for walking,
firing, dying, etc, and they have different sprites for different angles.
PLAYA1, PLAYA2A8, PLAYA3A7, PLAYA4A6, and PLAYA5 are all for the first frame
of the sequence used to display a walking (or running) player. 1 is the view
from the front, 2 and 8 mean from front-right and front-left (the same sprite
is used, and mirrored appropriately), 3 and 7 the side, 5 the back.
        Each picture has three sections, basically. First, a four-integer
header. Then a number of long-integer pointers. Then the picture pixel color
data.

[5-1]: Header
=============

        The header has four fields:

(1) Width. The number of columns of picture data.
(2) Height. The number of rows.
(3) Left offset. The number of pixels to the left of the center; where the
      first column gets drawn.
(4) Top offset. The number of pixels above the origin; where the top row is.

        The width and height define a rectangular space or limits for drawing
a picture within. To be "centered", (3) is usually about half of the total
width. If the picture had 30 columns, and (3) was 10, then it would be
off-center to the right, especially when the player is standing right in
front of it, looking at it. If a picture has 30 rows, and (4) is 60, it will
appear to "float" like a blue soul-sphere. If (4) equals the number of rows,
it will appear to rest on the ground. If (4) is less than that for an object,
the bottom part of the picture looks awkward.
        With walls patches, (3) is always (columns/2)-1, and (4) is always
(rows)-5. This is because the walls are drawn consistently within their own
space (There are two integers in each SIDEDEF which can offset the beginning
of a wall's texture).
        Finally, if (3) and (4) are NEGATIVE integers, then they are the
absolute coordinates from the top-left corner of the screen, to begin drawing
the picture, assuming the VIEW is FULL-SCREEN (the full 320x200). This is
only done with the picture of the doom player's current weapon - fist,
chainsaw, bfg9000, etc. The game engine scales the picture down appropriately
if the view is less than full-screen.

[5-2]: Pointers
===============

        After the header, there are N = (# of columns) long integers (4 bytes
each). These are pointers to the data for each COLUMN. The value of the
pointer represents the offset in bytes from the first byte of the picture
resource.

[5-3]: Pixel Data
=================

        Each column is composed of some number of BYTES (NOT integers),
arranged in "posts":
        The first byte is the row to begin drawing this post at. 0 means
whatever height the header (4) upwards-offset describes, larger numbers move
correspondingly down.
        The second byte is how many colored pixels (non-transparent) to draw,
going downwards.
        Then follow (# of pixels) + 2 bytes, which define what color each
pixel is, using the game palette. The first and last bytes AREN'T drawn, and
I don't know why they are there. Probably just leftovers from the creation
process on the NExT machines. Only the middle (# of pixels in this post) are
drawn, starting at the row specified in byte 1 of the post.
        After the last byte of a post, either the column ends, or there is
another post, which will start as stated above.
        255 (hex FF) ends the column, so a column that starts this way is a
null column, all "transparent". Goes to the next column.
        Thus, transparent areas can be defined for either items or walls.

---------------------------------------
CHAPTER [6]: Floor and Ceiling Textures
---------------------------------------

        All the names for these textures are in the directory between the
F_START and F_END entries. There is no look-up or meta-structure as with the
walls. Each texture is 4096 raw bytes, making a square 64 by 64 pixels, which
is pasted onto a floor or ceiling, with the same orientation as the automap
would imply, i.e. the first byte is the color at the NW corner, etc. The
blocks in the grid are 128 by 128, so four floor tiles will fit in each
block.
        The data in F_SKY1 isn't even used since the game engine interprets
that special ceiling as see-through to the SKY texture beyond. So the F_SKY1
entry can have zero length.
        As discussed in chapter [5], replacement and/or new-name floors don't
work right from pwad files, only in the main IWAD.
        You can change all the floors and ceilings you want by constructing a
new DOOM.WAD, but you have to make sure no floor or ceiling uses an entry
name which isn't in your F_ section. And you have to include these four entries,
although you can change their contents (pictures): FLOOR4_8, SFLR6_1,
MFLR8_4, and FLOOR7_2. The first three are needed as backgrounds for the
episode end texts. The last is what is displayed "outside" the display window
if the display is not full-screen.

[6-1]: Animated floors
----------------------

        See Chapter [8-4-1] for a discussion of how the animated walls and
floors work. Unfortunately, the fact that the floors all need to be lumped
together in one wad file means that its not possible to change the animations
via a pwad file, unless it contains ALL the floors, which amounts to several
hundred k. Plus you can't distribute the original data, so if you want to
pass your modification around, it must either have all the floors all-new,
or you must create some sort of program which will construct the wad from
the original DOOM.WAD plus your additions.

-----------------------------
CHAPTER [7]: Sounds and Songs
-----------------------------

[7-1]: D_[xxxxxx]
=================

        Songs.  What format are they? Apparently the MUS format, which I have
absolutely no knowledge of. But it's obvious what each song is for, from
their names.

[7-2]: DP[xxxxxx] and DS[xxxxxx]
================================

        These are the sound effects. They come in pairs - DP for pc speaker
sounds, DS for sound cards.
        The DS sounds are in RAW format: they have a four integer header,
then the sound samples (each is 1 byte since they are 8-bit samples).
        The headers' four (unsigned) integers are: 3, then 11025 (the sample
rate), then the number of samples, then 0. Since the maximum number of
samples is 65535, that means a little less than 6 seconds is the longest
possible sound effect.

-------------------------------------------------
CHAPTER [8]: Some Important Non-picture Resources
-------------------------------------------------

[8-1]: PLAYPAL
==============

        There are 14 palettes here, each is 768 bytes = 256 rgb triples. That
is, the first three bytes of a palette are the red, green, and blue portions
of color 0. And so on.
        Note that standard VGA boards whose palettes only encompass 262,144
colors only accept values of 0-63 for each channel (rgb), so the values would
need to be divided by 4.
        Palette 0 is the one that is used for almost everything.
        Palettes 10-12 are used (briefly) when an item is picked up, the more
items that are picked up in quick succession, the brighter it gets, palette
12 being the brightest.
        Palette 13 is used while wearing a radiation suit.
        Palettes 3, 2, then 0 again are used after getting berserk strength.
        If the player is hurt, then the palette shifts up to X, then comes
"down" one every half second or so, to palette 2, then palette 0 (normal)
again. What X is depends on how badly the player got hurt: Over 100% damage
(add health loss and armor loss), X=8. 93%, X=7. 81%, X=6. 55%, X=5. 35%,
X=4. 16%, X=2.

[8-2]: COLORMAP
===============

        This contains 34 sets of 256 bytes, which "map" the colors "down" in
brightness. Brightness varies from sector to sector. At very low brightness,
almost all the colors are mapped to black, the darkest gray, etc. At the
highest brightness levels, most colors are mapped to their own values,
i.e. they don't change.
        In each set of 256 bytes, byte 0 will have the number of the palette
color to which original color 0 gets mapped.
        The colormaps are numbered 0-33. Colormaps 0-31 are for the different
brightness levels, 0 being the brightest (light level 248-255), 31 being the
darkest (light level 0-7).
        Colormap 32 is used for every pixel in the display window (but not
the status bar), regardless of sector brightness, when the player is under the
effect of the "Invulnerability" power-up. This map is all whites/greys.
        Colormap 33 is all black for some reason.

[8-3]: DEMO[1-3]
================

        These are the demos that will be shown if you start doom, and do
nothing else. Demos can be created using the devparm parameter:

DOOM -devparm -record DEMONAME

        The extension .LMP is automatically added to the DEMONAME. Other
parameters may be used simultaneously, such as -skill [1-5], -warp [1-3]
[1-9], -file [pwad_filename], etc. The demos in the WAD are in exactly the
same format as these LMP files, so a LMP file may be simply pasted or
assembled into a WAD, and if its length and pointer directory entries are
correct, it will work.
        This is assuming the same version of the game, however. For some
illogical reason, demos made with 1.1 doom don't work in 1.2 doom, and vice
versa. If I had a pressing need to convert an old demo, I might try to
figure out why, but I don't.
        The game only accesses DEMO1, DEMO2, and DEMO3, so having more than
that in a pwad file is pointless.

[8-4]: TEXTURE1 and TEXTURE2
============================

        These resources contains a list of the wall names used in the various
SIDEDEFS sections of the level data. Each wall name actually references a
meta-structure, defined in this list. TEXTURE2 has all the walls that are
only in the registered version.
        First is a table of pointers to the start of the entries. There is a
long integer (say, N) which is the number of entries in the TEXTURE resource.
Then follow N long integers which are the offsets in bytes from the beginning
of the TEXTURE resource to the start of that texture's definition entry.
        Then follow N texture entries, which each consist of a 8-byte name
field and then a variable number of 2-byte integer fields:

(1) The name of the texture, used in SIDEDEFS, e.g. "STARTAN3".
(2) always 0.
(3) always 0.
(4) total width of texture
(5) total height of texture

        The fourth and fifth fields define a "space" (usually 128 by 128 or
64 by 72 or etc...) in which individual wall patches are placed to form the
overall picture. This is done because there are some wall patches that are
used in several different walls, like computer screens, etc. Note that to
tile properly in the vertical direction on a very tall wall, a texture has to
have height 128, the maximum. The maximum width is 256. The sum of the sizes
of all the wall patches used in a single texture must be <= 64k.

(6) always 0.
(7) always 0.
(8) Number of 5-field patch descriptors that follow. This is why each texture
    entry has variable length. Many entries have just 1 patch, one has 64!

        1. x offset from top-left corner of texture space defined in field
           4/5 to start placement of this patch
        2. y offset
        3. number, from 0 to whatever, of the entry in the PNAMES resource,
           which contains the name from the directory, of the wall patch to
           use...
        4. always 1, is for something called "stepdir"...
        5. always 0, is for "colormap"...

        The texture's entry ends after the last of its patch descriptors.
        Note that patches can have transparent parts, since they are in the
same picture format as everything else. Thus there can be (and are)
transparent wall textures. These should only be used on a border between two
sectors, to avoid the "displaying nothing" problems.
        Here is how one can add walls, while still retaining any of the
original ones it came with: in a pwad, have replacement entries for PNAMES
and TEXTURE2. These will be the same as the originals, but with more entries,
for the wall patches and assembled textures that you're adding. Then have
entries for every new name in PNAMES, as well as old names which you want to
associate to new pictures. You don't need to use the P_START and P_END
entries.

[8-4-1]: Animated walls
-----------------------

        It is possible to change the walls and floors that are animated, like
the green blocks with a sewer-like grate that's spewing green slime
(SLADRIPx). The game engine sets up as many as 8 animation cycles for walls
based on the entries in the TEXTURE resources, and up to 5 based on what's
between F_START and F_END. The entries in FirstTexture and LastTexture,
below, and all the entries between them (in the order that they occur in a
TEXTURE list), are linked. If one of them is called by a sidedef, that sidedef
will change texture to the next in the cycle about 5 times a second , going back
to First after Last. Note that the entries between First and Last need not
be the same in number as in the original, nor do they have to follow the same
naming pattern, though that would probably be wise. E.g. one could set up
ROCKRED1, ROCKREDA, ROCKREDB, ROCKREDC, ROCKREDD, ROCKREDE, ROCKRED3 for
a 7-frame animated wall!
        If First and Last aren't in either TEXTURE, no problem. Then that
cycle isn't used. But if First is, and Last either isn't or is listed
BEFORE First, then an error occurs.

FirstTexture    LastTexture     Normal # of frames

BLODGR1         BLODGR4         4
BLODRIP1        BLODRIP4        4
FIREBLU1        FIREBLU2        2
FIRELAV3        FIRELAVA        2
FIREMAG1        FIREMAG3        3
FIREWALA        FIREWALL        3
GSTFONT1        GSTFONT3        3
ROCKRED1        ROCKRED3        3
SLADRIP1        SLADRIP3        3


(floor/ceiling animations) -

NUKAGE1         NUKAGE3         3
FWATER1         FWATER3         3
SWATER1         SWATER4         4
LAVA1           LAVA4           4
BLOOD1          BLOOD3          3

        Note that the SWATER entries aren't in the regular DOOM.WAD.

[8-5]: PNAMES
=============

        This is a lookup table for the numbers in TEXTURE[1 or 2] to
reference to an actual entry in the directory which is a wall patch (in the
picture format described in chapter [5]).
        The first two bytes of the PNAMES resource is an integer P which is
how many entries there are in the list.
        Then come P 8-byte names, each of which duplicates an entry in the
directory. If a patch name can't be found in the directory (including the
external pwad's directories), an error will occur. This naming of resources
is apparently not case-sensitive, lowercase letters will match uppercase.
        The middle integer of each 5-integer "set" of a TEXTURE1 entry is
something from 0 to whatever. Number 0 means the first entry in this PNAMES
list, 1 is the second, etc...

        Thanks for reading the "Official" DOOM Specs!
--
----------- Hank Leukart ------------ |   "Official" DOOM FAQ v5.8 Writer
--- ([e-mail]) --- |   FAQ by E-mail or "ftp.uwp.edu"
------------------------------------- |     "Official" DOOM FTP Site:
------------------------------------- |      ftp.orst.edu: /pub/doom