HOM is also an acronym for the
Hall Of Mirrors effect, the bane of
3d computer game level designers. A HOM is when
somehow a
map ends up with a kind of
hole, or a place where the
geometry is
messed up or
too complicated for the
game engine to deal with correctly. Visually, it appears as a sort of
hall of mirrors; reflections of reflections of reflections of the immediate area. Often times it
slows down the level considerably.
HOM is a major problem for mappers in the
Quake games due to the '
additive' way those levels are made. In
Quake,
Quake 2,
Quake 3: Arena, and related
games, levels are made by adding chunks of
geometry. If one misses a little area which opens up into the surrounding
void, a HOM results.
In
Unreal engine games it is a little easier to avoid HOM because levels can be constructed using both
additive and
subtractive techniques. This means that
structure can be both added and subtracted, so it is easier to avoid the sort of
leaks one finds in
Quake engine games.
Going completely subtractive does not remove the risk of HOM though, as
Jedi Knight had a level system which was completely
subtractive, and HOM was still an issue.
Amusingly, one of the
multiplayer levels for the
Jedi Knight expansion pack, '
Mysteries of the Sith', used HOM on purpose for its interesting
visual effect. In an area of this particular city level there was a
spaceport where there were a few ships landed. Underneath the grating on the ground there was a HOM, which looked really interesting. Kind of a
fans stuck in a
hall of mirrors look.