Mobj

A mobj, short for map object, is a type of thinker that roughly corresponds to things: players, monsters, items, obstacles and decorations, map spots such as teleport destinations or boss shooter destinations, and so on, are all map objects. Mobjs are also frequently called actors. Code comments present them as such:

//  MapObj data. Map Objects or mobjs are actors, entities,
//  thinker, take-your-pick... anything that moves, acts, or
//  suffers state changes of more or less violent nature.

In the source code, mobjs are represented by the mobjtype_t enum and the mobj_t and mobjinfo_t structures. The order in which the mobj types are declared in the info.h and info.c files corresponds to their DeHackEd number, and most DeHackEd changes consist in altering the values of the mobjinfos' properties. The mobjinfo corresponds to the "class" of a mobj (for example, imp) whereas the mobj corresponds to a particular "instance" of the class (for example, the imp that waits in the exit room of E1M1). The mobjinfo_t structure determines how many hit points a mobj starts with, which states it uses, what its flags are, what sounds it makes, what is its reaction time, its movement speed, and so on. The mobj_t structure stores its current position and momentum, which sector it is in, what is its current state, its current target, where it should respawn in Nightmare! mode, and so on.

Flags

The original Doom source code defined the following mobj flags (as enum mobjflag_t in file p_mobj.h).

Symbolic constant	Bit(s)	Value (decimal)	Value (hex)	Source code comment
MF_SPECIAL	0	1	0x1	Call P_SpecialThing when touched.
MF_SOLID	1	2	0x2	Blocks.
MF_SHOOTABLE	2	4	0x4	Can be hit.
MF_NOSECTOR	3	8	0x8	Don't use the sector links (invisible but touchable).
MF_NOBLOCKMAP	4	16	0x10	Don't use the blocklinks (inert but displayable)
MF_AMBUSH	5	32	0x20	Not to be activated by sound, deaf monster.
MF_JUSTHIT	6	64	0x30	Will try to attack right back.
MF_JUSTATTACKED	7	128	0x80	Will take at least one step before attacking.
MF_SPAWNCEILING	8	256	0x100	On level spawning (initial position), hang from ceiling instead of stand on floor.
MF_NOGRAVITY	9	512	0x200	Don't apply gravity (every tic), that is, object will float, keeping current height or changing it actively.
MF_DROPOFF	10	1024	0x400	This allows jumps from high places.
MF_PICKUP	11	2048	0x800	For players, will pick up items.
MF_NOCLIP	12	4096	0x1000	Player cheat. ???
MF_SLIDE	13	8192	0x2000	Player: keep info about sliding along walls.
MF_FLOAT	14	16384	0x4000	Allow moves to any height, no gravity. For active floaters, e.g. cacodemons, pain elementals.
MF_TELEPORT	15	32768	0x8000	Don't cross lines or ??? look at heights on teleport.
MF_MISSILE	16	65536	0x10000	Don't hit same species, explode on block. Player missiles as well as fireballs of various kinds.
MF_DROPPED	17	131072	0x20000	Dropped by a demon, not level spawned. E.g. ammo clips dropped by dying former humans.
MF_SHADOW	18	262144	0x40000	Use fuzzy draw (shadow demons or spectres), temporary player invisibility powerup.
MF_NOBLOOD	19	524288	0x80000	Flag: don't bleed when shot (use puff), barrels and shootable furniture shall not bleed.
MF_CORPSE	20	1048576	0x100000	Don't stop moving halfway off a step, that is, have dead bodies slide down all the way.
MF_INFLOAT	21	2097152	0x200000	Floating to a height for a move, ??? don't auto float to target's height.
MF_COUNTKILL	22	4194304	0x400000	On kill, count this enemy object towards intermission kill total. Happy gathering.
MF_COUNTITEM	23	8388608	0x800000	On picking up, count this item object towards intermission item total.
MF_SKULLFLY	24	16777216	0x1000000	Special handling: skull in flight. Neither a cacodemon nor a missile.
MF_NOTDMATCH	25	33554432	0x2000000	Don't spawn this object in death match mode (e.g. key cards).
MF_TRANSLATION	26, 27	201326592	0xC000000	Player sprites in multiplayer modes are modified using an internal color lookup table for re-indexing. If 0x4 0x8 or 0xc, use a translation table for player colormaps
MF_TRANSSHIFT	1, 3, 4	26	0x1A	Hmm ???.

External links

• File p_mobj.h from the original Doom source code release