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.
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_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 ???.|
References and notes
- File p_mobj.h, dated 1997 December 22, 8966 bytes, MD5 98518af2f9fc2cb5d5d7bde8901e5bb6
- Bits are conventionally numbered from zero. The first bit is bit 0, the second bit is bit 1, and so on.
- Question marks and other indications of uncertainty are as given in the original code.