Doom WAD map lumps

A Doom map is two-dimensional: a floor plan of lines, with a floor and ceiling height for each area. A map in a WAD is an empty marker lump with the map’s name and then these lumps, always in this order. Each of the first eight is an array of fixed-size records with nothing before the first or after the last. Numbers are 16-bit and little-endian, signed (i16) unless marked u16; positions are in map units, x growing east and y north. Records refer to one another by their number in their lump, counting from 0.

E1M1Marker the map’s name, no data0 bytes
THINGSThings monsters, items, player starts10 bytes each
LINEDEFSLines the walls and edges of the plan14 bytes each
SIDEDEFSSides the textures on each side of a line30 bytes each
VERTEXESVertices the points lines join4 bytes each
SEGSSegs lines cut up by the node builder12 bytes each
SSECTORSSubsectors convex areas, each a run of segs4 bytes each
NODESNodes the BSP tree28 bytes each
SECTORSSectors areas with floor and ceiling26 bytes each
REJECTReject table sector-to-sector sightvaries
BLOCKMAPBlockmap lines by 128-unit blockvaries

The lumps of a map in Doom’s format, in directory order

A map editor writes the first four lumps and SECTORS. A node builder works out SEGS, SSECTORS, NODES, REJECT and BLOCKMAP from them, for the engine’s drawing, collisions and sight checks.

THINGS

Offset	Size	Type	Name	Description
0	2	i16	x	Position east–west.
2	2	i16	y	Position north–south.
4	2	i16	angle	The way it faces in degrees: 0 east, 90 north, 180 west, 270 south.
6	2	i16	type	What it is: the thing’s number in the game’s table, such as 1 for player 1’s start or 3001 for an imp.
8	2	i16	options	Flags, below.

Bit	Value	Meaning
0	1	Present on skills 1 and 2
1	2	Present on skill 3
2	4	Present on skills 4 and 5
3	8	Ambush: the monster stays put until it sees a player, whatever it hears
4	16	Only in multiplayer games

Doom ignores the other bits. Boom later used bit 5 (not in deathmatch) and bit 6 (not in co-op), and MBF bit 7 (friendly).

0x 40 00 (64)2 bytes
2y C0 FF (−64)2 bytes
4angle 5A 00 (90, north)2 bytes
6type 01 00 (player 1 start)2 bytes
8options 07 00 (every skill)2 bytes

An invented thing

LINEDEFS

Offset	Size	Type	Name	Description
0	2	i16	v1	The vertex the line starts at.
2	2	i16	v2	The vertex it ends at. Looking from v1 to v2, the right side is the front.
4	2	i16	flags	Flags, below.
6	2	i16	special	What happens when the line is crossed, pressed or shot: a door, a lift, a teleporter, the exit. 0 for none.
8	2	i16	tag	The special acts on the sectors with this tag.
10	2	i16	sidenum[0]	The right sidedef.
12	2	i16	sidenum[1]	The left sidedef, or −1 (`FF FF`) for a one-sided line.

Bit	Value	Name in the source	Meaning
0	1	ML_BLOCKING	Blocks players and monsters
1	2	ML_BLOCKMONSTERS	Blocks monsters only
2	4	ML_TWOSIDED	Two-sided: there is a sector on both sides
3	8	ML_DONTPEGTOP	Upper texture unpegged: drawn from the top down
4	16	ML_DONTPEGBOTTOM	Lower texture unpegged
5	32	ML_SECRET	Shown on the automap as a one-sided wall
6	64	ML_SOUNDBLOCK	Sound passing two of these stops
7	128	ML_DONTDRAW	Never shown on the automap
8	256	ML_MAPPED	Shown on the automap from the start

Boom later used bit 9 to let a pressed line pass the use on to lines behind it.

SIDEDEFS

Offset	Size	Type	Name	Description
0	2	i16	textureoffset	How far the textures are moved along the wall.
2	2	i16	rowoffset	How far they are moved up or down.
4	8	ASCII	toptexture	The upper texture, drawn above an opening where the ceiling beyond is lower. `-` for none.
12	8	ASCII	bottomtexture	The lower texture, drawn below an opening where the floor beyond is higher.
20	8	ASCII	midtexture	The wall itself on a one-sided line; on a two-sided line usually `-`, or a see-through texture.
28	2	i16	sector	The sector this side faces into.

VERTEXES

Two 16-bit numbers each: x at offset 0 and y at offset 2. The node builder adds vertices of its own at the end, where it splits lines into segs.

SEGS

Offset	Size	Type	Name	Description
0	2	i16	v1	Start vertex.
2	2	i16	v2	End vertex.
4	2	i16	angle	Direction, in units of 1/65536 of a turn: 0 east, 16384 north, −32768 west, −16384 south.
6	2	i16	linedef	The line the seg is part of.
8	2	i16	side	0 for the line’s right side, 1 for its left.
10	2	i16	offset	How far along the line the seg starts.

SSECTORS

Each subsector is a convex area of one sector, bounded by a run of segs: the number of segs (offset 0) and the first of them (offset 2), 4 bytes in all.

NODES

The binary space partition tree the engine draws with. Each node splits the area below it in two along a line. The last node is the root.

Offset	Size	Type	Name	Description
0	2	i16	x	A point on the partition line.
2	2	i16	y
4	2	i16	dx	The line’s direction.
6	2	i16	dy
8	8	i16 × 4	bbox[0]	The right child’s bounding box: top, bottom, left, right.
16	8	i16 × 4	bbox[1]	The left child’s bounding box.
24	2	u16	children[0]	The right child: a node number, or with bit 15 (`8000`, NF_SUBSECTOR) set a subsector number.
26	2	u16	children[1]	The left child, the same way.

SECTORS

Offset	Size	Type	Name	Description
0	2	i16	floorheight	The height of the floor.
2	2	i16	ceilingheight	The height of the ceiling.
4	8	ASCII	floorpic	The flat on the floor.
12	8	ASCII	ceilingpic	The flat on the ceiling; `F_SKY1` shows the sky.
20	2	i16	lightlevel	Brightness, 0 to 255.
22	2	i16	special	An effect: flickering light, damage, a secret. 0 for none.
24	2	i16	tag	Line specials with the same tag act on this sector.

REJECT

A table of one bit for each pair of sectors, which lets the engine skip line-of-sight checks. Bit number a × sectors + b is set when a monster in sector a can never see a player in sector b. Bits are taken from the lowest bit of each byte first. The lump is (sectors² + 7) ÷ 8 bytes, rounded down; many node builders write it all zeros, which makes the engine check every time.

BLOCKMAP

A grid of 128 × 128 unit blocks over the map, and for each block the lines that touch it, for collision checks.

Offset	Size	Type	Name	Description
0	2	i16	x origin	The west edge of the grid.
2	2	i16	y origin	The south edge of the grid.
4	2	i16	columns	Blocks across.
6	2	i16	rows	Blocks up.
8	2 each	u16	offsets	For each block, row by row from the south-west, eastwards first: where its list starts, counted in 2-byte words from the start of the lump.
…	varies	u16	lists	Each list is a 0, the numbers of the lines in the block, and −1 (`FF FF`). Blocks with the same lines can share a list.

0Header 00 00 00 00 01 00 01 00: one block from 0, 08 bytes
8Offset 05 00: the list starts at word 5, byte 102 bytes
10List 00 00, lines 00 00 01 00, then FF FF8 bytes

An invented blockmap of one block touched by lines 0 and 1

Hexen’s format

Hexen’s maps have an eleventh lump, BEHAVIOR, holding compiled ACS scripts (it starts ACS and a zero byte), and give things and lines more fields. A map with a BEHAVIOR lump is in Hexen’s format; ZDoom and later ports also use it for Doom maps. The other lumps are as in Doom.

Offset	Size	Type	Name	Description
0	2	i16	tid	A thing ID that scripts and specials refer to; 0 for none.
2	2	i16	x	Position east–west.
4	2	i16	y	Position north–south.
6	2	i16	height	Height above the floor.
8	2	i16	angle	Facing, in degrees.
10	2	i16	type	What it is.
12	2	i16	flags	1, 2, 4 skills; 8 ambush; 16 dormant; 32 fighter, 64 cleric, 128 mage; 256 single player, 512 co-op, 1024 deathmatch.
14	1	u8	special	An action run when the thing dies or is picked up.
15	5	u8 × 5	args	The action’s five arguments.

A thing in Hexen’s format: 20 bytes.

Offset	Size	Type	Name	Description
0	2	i16	v1	Start vertex.
2	2	i16	v2	End vertex.
4	2	i16	flags	Doom’s bits 0 to 8; bit 9 (512) repeatable; bits 10 to 12 how the special is set off: 0 player crosses, 1 player uses, 2 monster crosses, 3 projectile hits, 4 player bumps, 5 projectile crosses.
6	1	u8	special	The action number.
7	5	u8 × 5	args	Its arguments: a tag, a speed, a script number and so on.
12	2	i16	sidenum[0]	The right sidedef.
14	2	i16	sidenum[1]	The left sidedef, or −1.

A line in Hexen’s format: 16 bytes. There is no tag field: the specials take their tag as an argument.

Later map formats

Source ports added other ways to store a map. UDMF keeps the whole map as text in a TEXTMAP lump after the marker, up to an ENDMAP marker. GL node builders add lumps such as GL_VERT and GL_SEGS after a second marker named GL_ and the map’s name, and ZDoom can keep compressed nodes in ZNODES. The explorer names these lumps and shows TEXTMAP as text, but draws only maps in Doom’s and Hexen’s formats.

.WAD File Format – Map lumps