Thing

Things represent players, monsters, pick-ups, and projectiles. Inside the game, these are known as actors, or mobjs. They also represent obstacles, certain decorations, player start positions and teleport landing sites.

While some mobjs, such as projectiles and special effects, can only be created during play, most things can be placed in a map from a map editor through an associated editor number. When the map is loaded, an actor that corresponds to that number will be spawned at the location of that map thing. See thing types for a listing of all things that have an associated editor number.

THINGS lump[edit]

Doom level format
Things Linedefs Sidedefs Vertices Segs Subsectors Nodes Sectors Reject Blockmap
Extensions: Behavior FraggleScript ACS GL nodes Macros Leafs

Level thing data is stored in the THINGS lump. Each entry is 10 bytes long. This format is used by both Doom and Heretic.

Offset	Size (bytes)	C99 type	Description
0	2	int16_t	x position
2	2	int16_t	y position
4	2	int16_t	Angle facing
6	2	int16_t	DoomEd thing type
8	2	int16_t	Flags

Flags[edit]

bit	hex	description
0	0x0001	Thing is on skill levels 1 & 2
1	0x0002	Thing is on skill level 3
2	0x0004	Thing is on skill levels 4 & 5
3	0x0008	Thing is waiting in ambush. Commonly known as "deaf" flag. In fact, it does not render monsters deaf per se.
4	0x0010	Thing is not in single player

Boom flags[edit]

Boom adds the flags:

bit	hex	description
5	0x0020	Thing is not in deathmatch
6	0x0040	Thing is not in coop

MBF flag[edit]

MBF adds the flag:

bit	hex	description
7	0x0080	Friendly monster

Hexen format[edit]

Hexen extended upon the things lump. Hexen things may contain an action special which is executed upon death or pickup of the thing (for monsters and items, respectively). Hexen format also introduced true z-clipping, allowing placement of monsters on the z-axis. Finally, Hexen monsters are also able to have a tag similar to sectors. This is called the thing ID or TID.

Offset	Size (bytes)	C99 type	Description
0	2	int16_t	Thing id (tid)
2	2	int16_t	X position
4	2	int16_t	Y position
6	2	int16_t	Starting height
8	2	int16_t	Angle facing
10	2	int16_t	DoomEd thing type
12	2	int16_t	Flags
14	1	uint8_t	Hexen action special
15	1	uint8_t	Argument 1
16	1	uint8_t	Argument 2
17	1	uint8_t	Argument 3
18	1	uint8_t	Argument 4
19	1	uint8_t	Argument 5

Note that Hexen things are 20 bytes in size; 10 bytes larger than things in Doom.

Hexen flags[edit]

bit	hex	description
0	0x0001	Thing is on skill levels 1 & 2
1	0x0002	Thing is on skill level 3
2	0x0004	Thing is on skill levels 4 & 5
3	0x0008	Thing is waiting in ambush
4	0x0010	Thing is dormant - it will not wake up until it is activated using Thing_Activate
5	0x0020	Thing appears to the Fighter class
6	0x0040	Thing appears to the Cleric class
7	0x0080	Thing appears to the Mage class
8	0x0100	Thing appears in single-player games
9	0x0200	Thing appears in cooperative games
10	0x0400	Thing appears in deathmatch games

Strife format[edit]

Strife did not alter the thing structure like Hexen did, however it did make use of the unused flag bits.

Strife flags[edit]

bit	hex	description
0	0x0001	Thing is on skill levels 1 & 2
1	0x0002	Thing is on skill level 3
2	0x0004	Thing is on skill levels 4 & 5
3	0x0008	Thing stands still (only useful for specific enemies)
4	0x0010	Thing will not appear in single player
5	0x0020	Thing is waiting in ambush
6	0x0040	Thing is a friendly monster
7	0x0080	Unused
8	0x0100	Thing is 25% translucent
9	0x0200	Thing is either invisible, or 75% translucent if combined with bit 8.

Doom 64 format[edit]

The Doom 64 THING format is similar to the Doom format except for the inclusion of a z position and an ID. Each entry is 14 bytes long.

Offset	Size (bytes)	C99 type	Description
0	2	int16_t	x position
2	2	int16_t	y position
4	2	int16_t	z position
6	2	int16_t	Angle facing
8	2	int16_t	DoomEd thing type
10	2	int16_t	Flags
12	2	int16_t	ID

Doom 64 flags[edit]

Additional flags are defined in comparison to the Doom format, however flags 10 through 12 are not used in any Doom 64 maps.

bit	hex	description
0	0x0001	Thing is on skill levels 1 & 2
1	0x0002	Thing is on skill level 3
2	0x0004	Thing is on skill level 4
3	0x0008	Thing is waiting in ambush
4	0x0010	Thing is not in single player (unused)
5	0x0020	Thing doesn't spawn until triggered in level
6	0x0040	Thing triggers something when picked up
7	0x0080	Thing triggers something when killed
8	0x0100	Thing counts as secret in intermission screen
9	0x0200	Thing ignores other attackers (no infighting)
10	0x0400	No operation (unused)

Because vanilla Doom 64 lacks multiplayer, bit 4 is essentially unused. Bit 10 is recognized, but the game does not attempt to do anything with it, likely as a result of code being reused from other versions of Doom.

Doom64 EX flags[edit]

Doom64 EX adds the flags:

bit	hex	description
10	0x0400	Thing doesn't spawn in deathmatch games
11	0x0800	Thing doesn't in standard netgame mode

Doom 64 (2020 version) flags[edit]

Doom 64 (2020 version) adds the flag:

bit	hex	description
12	0x1000	Thing is a nightmare monster

Sources[edit]

Unofficial Doom Specs
Boom source code: boomref.txt
Doom 64 Tech Bible at Doomworld/idgames
Doom 64 multiplayer actor flags on Doomworld forums