<s>
The	O
Quake	B-Application
engine	I-Application
is	O
the	O
game	O
engine	O
developed	O
by	O
id	O
Software	O
to	O
power	O
their	O
1996	O
video	O
game	O
Quake	B-Application
.	O
</s>
<s>
It	O
featured	O
true	O
3D	O
real-time	B-General_Concept
rendering	I-General_Concept
and	O
is	O
now	O
licensed	O
under	O
the	O
terms	O
of	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
v2.0	I-License
or	I-License
later	I-License
.	O
</s>
<s>
Much	O
of	O
the	O
engine	O
remained	O
in	O
Quake	B-Application
II	I-Application
and	O
Quake	B-Application
III	I-Application
Arena	I-Application
.	O
</s>
<s>
The	O
Quake	B-Application
engine	I-Application
,	O
like	O
the	O
Doom	B-Application
engine	I-Application
,	O
used	O
binary	O
space	O
partitioning	O
(	O
BSP	O
)	O
to	O
optimise	O
the	O
world	O
rendering	O
.	O
</s>
<s>
The	O
Quake	B-Application
engine	I-Application
also	O
used	O
Gouraud	B-Algorithm
shading	I-Algorithm
for	O
moving	O
objects	O
,	O
and	O
a	O
static	O
lightmap	B-Data_Structure
for	O
nonmoving	O
objects	O
.	O
</s>
<s>
Historically	O
,	O
the	O
Quake	B-Application
engine	I-Application
has	O
been	O
treated	O
as	O
a	O
separate	O
engine	O
from	O
its	O
successor	O
,	O
the	O
Quake	B-Application
II	I-Application
engine	I-Application
.	O
</s>
<s>
Although	O
the	O
codebases	O
for	O
Quake	B-Application
and	O
Quake	B-Application
II	I-Application
were	O
separate	O
GPL	B-License
releases.	O
,	O
both	O
engines	O
are	O
now	O
considered	O
variants	O
of	O
id	B-Application
Tech	I-Application
2	I-Application
.	O
</s>
<s>
The	O
Quake	B-Application
engine	I-Application
was	O
developed	O
from	O
1995	O
for	O
the	O
video	O
game	O
Quake	B-Application
,	O
released	O
on	O
June	O
22	O
,	O
1996	O
.	O
</s>
<s>
John	O
Carmack	O
did	O
most	O
of	O
the	O
programming	O
of	O
the	O
engine	O
,	O
with	O
help	O
from	O
Michael	O
Abrash	O
in	O
algorithms	O
and	O
assembly	B-Language
optimization	O
.	O
</s>
<s>
The	O
Quake	B-Application
II	I-Application
engine	I-Application
(	O
id	B-Application
Tech	I-Application
2	I-Application
)	O
was	O
based	O
on	O
it	O
.	O
</s>
<s>
John	O
Romero	O
initially	O
conceived	O
of	O
Quake	B-Application
as	O
an	O
action	B-Application
game	I-Application
taking	O
place	O
in	O
a	O
fully	O
3D	O
polygon	O
world	O
,	O
inspired	O
by	O
Sega	O
AM2	O
's	O
3D	O
fighting	O
game	O
Virtua	B-Application
Fighter	I-Application
.	O
</s>
<s>
Quake	B-Application
was	O
also	O
intended	O
to	O
feature	O
Virtua	O
Fighter-influenced	O
third-person	O
melee	B-Application
combat	I-Application
.	O
</s>
<s>
Quake	B-Application
was	O
the	O
first	O
true-3D	O
game	O
to	O
use	O
a	O
special	O
map	O
design	O
system	O
that	O
preprocessed	O
and	O
pre-rendered	O
some	O
elements	O
of	O
the	O
3D	O
environment	O
,	O
so	O
as	O
to	O
reduce	O
the	O
processing	O
required	O
when	O
playing	O
the	O
game	O
on	O
the	O
50	O
–	O
75MHz	O
CPUs	B-Device
of	O
the	O
time	O
.	O
</s>
<s>
The	O
map	O
editor	O
program	O
uses	O
a	O
number	O
of	O
simple	O
convex	O
3D	O
geometric	O
objects	O
known	O
as	O
brushes	B-Application
that	O
are	O
sized	O
and	O
rotated	O
to	O
build	O
the	O
environment	O
.	O
</s>
<s>
The	O
brushes	B-Application
are	O
placed	O
and	O
oriented	O
to	O
create	O
an	O
enclosed	O
,	O
empty	O
,	O
volumetric	O
space	O
,	O
and	O
when	O
the	O
design	O
is	O
complete	O
,	O
the	O
map	O
is	O
run	O
through	O
the	O
rendering	O
preprocessor	O
.	O
</s>
<s>
The	O
preprocessor	O
is	O
used	O
to	O
locate	O
two	O
types	O
of	O
empty	O
space	O
in	O
the	O
map	O
:	O
the	O
empty	O
space	O
enclosed	O
by	O
brushes	B-Application
where	O
the	O
game	O
will	O
be	O
played	O
and	O
the	O
other	O
empty	O
space	O
outside	O
the	O
brushes	B-Application
that	O
the	O
player	O
will	O
never	O
see	O
.	O
</s>
<s>
The	O
preprocessor	O
then	O
strips	O
away	O
the	O
back	O
faces	O
of	O
the	O
individual	O
brushes	B-Application
,	O
which	O
are	O
outside	O
the	O
game	O
space	O
,	O
leaving	O
only	O
a	O
few	O
polygons	O
that	O
define	O
the	O
outer	O
perimeter	O
of	O
the	O
enclosed	O
game	O
space	O
.	O
</s>
<s>
Generally	O
,	O
once	O
a	O
map	O
has	O
been	O
preprocessed	O
,	O
it	O
cannot	O
be	O
re-edited	O
in	O
a	O
normal	O
fashion	O
because	O
the	O
original	O
brushes	B-Application
have	O
been	O
cut	O
into	O
small	O
pieces	O
.	O
</s>
<s>
Instead	O
,	O
the	O
original	O
map	O
editor	O
data	O
with	O
the	O
brushes	B-Application
is	O
retained	O
and	O
used	O
to	O
create	O
new	O
versions	O
of	O
the	O
map	O
.	O
</s>
<s>
Though	O
difficult	O
,	O
this	O
technique	O
was	O
occasionally	O
used	O
by	O
cheaters	O
to	O
create	O
windows	O
in	O
walls	O
,	O
to	O
see	O
normally	O
hidden	O
enemies	O
approaching	O
from	O
behind	O
doors	O
and	O
walls	O
,	O
and	O
resulted	O
in	O
an	O
anti-cheat	O
mechanism	O
used	O
in	O
recent	O
3D	O
games	O
that	O
calculates	O
a	O
checksum	B-Algorithm
for	O
each	O
file	O
used	O
in	O
the	O
game	O
,	O
to	O
detect	O
players	O
using	O
potentially	O
hacked	O
map	O
files	O
.	O
</s>
<s>
To	O
prevent	O
leaks	O
,	O
the	O
brushes	B-Application
should	O
overlap	O
and	O
slightly	O
interpenetrate	O
each	O
other	O
;	O
attempting	O
to	O
perfectly	O
align	O
along	O
the	O
edges	O
of	O
unusually	O
shaped	O
brushes	B-Application
on	O
a	O
grid	O
can	O
result	O
in	O
very	O
small	O
gaps	O
that	O
are	O
difficult	O
to	O
locate	O
.	O
</s>
<s>
The	O
open	O
sky	O
in	O
Quake	B-Application
maps	O
is	O
in	O
fact	O
not	O
open	O
,	O
but	O
is	O
covered	O
over	O
and	O
enclosed	O
with	O
large	O
brushes	B-Application
,	O
and	O
textured	O
with	O
a	O
special	O
skybox	O
texture	O
,	O
which	O
is	O
programmed	O
to	O
use	O
sphere	B-General_Concept
mapping	I-General_Concept
,	O
and	O
thus	O
always	O
looks	O
the	O
same	O
from	O
any	O
viewing	O
position	O
,	O
giving	O
the	O
illusion	O
of	O
a	O
distant	O
sky	O
.	O
</s>
<s>
Quake	B-Application
also	O
incorporated	O
the	O
use	O
of	O
lightmaps	B-Data_Structure
and	O
3D	O
light	O
sources	O
,	O
as	O
opposed	O
to	O
the	O
sector-based	O
static	O
lighting	O
used	O
in	O
games	O
of	O
the	O
past	O
.	O
</s>
<s>
id	O
Software	O
's	O
innovation	O
has	O
been	O
used	O
for	O
many	O
3D	O
games	O
released	O
since	O
,	O
particularly	O
first-person	O
shooters	O
,	O
though	O
id	O
Software	O
switched	O
to	O
a	O
Unified	O
lighting	O
and	O
shadowing	O
model	O
for	O
Doom	B-Application
3	I-Application
(	O
however	O
,	O
they	O
switched	O
back	O
to	O
a	O
lightmapped	O
or	O
semi-lightmapped	O
method	O
starting	O
with	O
RAGE	B-Application
)	O
.	O
</s>
<s>
After	O
a	O
map	O
had	O
been	O
pruned	O
of	O
excess	O
polygons	O
,	O
a	O
second	O
preprocessing	O
system	O
was	O
used	O
to	O
precalculate	O
and	O
bake	O
the	O
lightmaps	B-Data_Structure
into	O
the	O
game	O
map	O
to	O
further	O
reduce	O
load	O
on	O
the	O
CPU	B-Device
when	O
playing	O
the	O
game	O
.	O
</s>
<s>
The	O
Quake	B-Application
engine	I-Application
was	O
optimized	O
specifically	O
to	O
obviate	O
this	O
problem	O
.	O
</s>
<s>
The	O
engine	O
could	O
be	O
told	O
ahead	O
of	O
time	O
to	O
not	O
calculate	O
rendering	O
for	O
all	O
objects	O
in	O
any	O
space	O
out	O
of	O
the	O
player	O
's	O
view	O
,	O
greatly	O
reducing	O
the	O
rendering	O
load	O
on	O
the	O
CPU	B-Device
.	O
</s>
<s>
It	O
is	O
uncommon	O
in	O
the	O
original	O
Quake	B-Application
to	O
be	O
able	O
to	O
see	O
across	O
the	O
entire	O
length	O
of	O
a	O
map	O
,	O
and	O
outdoor	O
spaces	O
are	O
often	O
very	O
tall	O
and	O
narrow	O
,	O
primarily	O
utilizing	O
distance	O
above	O
into	O
open	O
sky	O
or	O
below	O
into	O
lava	O
to	O
create	O
a	O
low-polygonal	O
illusion	O
of	O
expanse	O
.	O
</s>
<s>
For	O
each	O
area	O
,	O
the	O
VSD	B-Algorithm
algorithm	O
finds	O
the	O
parts	O
of	O
the	O
map	O
for	O
which	O
a	O
line	O
of	O
sight	O
exists	O
.	O
</s>
<s>
John	O
Carmack	O
realized	O
that	O
one	O
area	O
sees	O
just	O
a	O
small	O
fraction	O
of	O
the	O
other	O
areas	O
,	O
so	O
he	O
compressed	O
this	O
information	O
by	O
using	O
run-length	B-Algorithm
encoding	I-Algorithm
(	O
RLE	O
)	O
.	O
</s>
<s>
This	O
is	O
what	O
allowed	O
Quakes	B-Application
complex	O
geometry	O
to	O
be	O
rendered	O
so	O
quickly	O
on	O
the	O
hardware	O
of	O
the	O
time	O
.	O
</s>
<s>
The	O
pixel	O
rendering	O
loop	O
was	O
implemented	O
in	O
assembly	B-Language
.	O
</s>
<s>
The	O
texture	O
coordinates	O
perspective	O
correction	O
and	O
interpolation	B-Algorithm
was	O
done	O
using	O
the	O
floating-point	B-General_Concept
unit	I-General_Concept
,	O
due	O
to	O
the	O
limited	O
number	O
of	O
integer	O
registers	O
;	O
it	O
also	O
allows	O
to	O
compute	O
expensive	O
division	O
operation	O
(	O
part	O
of	O
perspective	O
correction	O
)	O
on	O
the	O
floating-point	B-General_Concept
unit	I-General_Concept
in	O
parallel	O
with	O
integer	O
interpolation	B-Algorithm
(	O
in	O
other	O
words	O
,	O
at	O
no	O
cost	O
)	O
.	O
</s>
<s>
The	O
base	O
texture	O
and	O
the	O
lightmap	B-Data_Structure
of	O
a	O
wall	O
were	O
rendered	O
at	O
the	O
same	O
time	O
:	O
a	O
"	O
surface	O
cache	O
"	O
was	O
creating	O
new	O
surfaces	O
,	O
which	O
are	O
new	O
pre-lighted	O
textures	O
which	O
combines	O
the	O
base	O
and	O
light	B-Data_Structure
map	I-Data_Structure
textures	O
baked	O
together	O
.	O
</s>
<s>
To	O
save	O
memory	O
,	O
smaller	O
surfaces	O
using	O
mipmaps	B-Data_Structure
of	O
the	O
original	O
texture	O
were	O
generated	O
first	O
for	O
further	O
walls	O
.	O
</s>
<s>
Quake	B-Application
was	O
one	O
of	O
the	O
first	O
games	O
to	O
support	O
3D	O
hardware	B-General_Concept
acceleration	I-General_Concept
.	O
</s>
<s>
While	O
initially	O
released	O
with	O
only	O
software	O
rendering	O
,	O
John	O
Carmack	O
created	O
a	O
version	O
of	O
the	O
Quake	B-Application
executable	O
that	O
took	O
advantage	O
of	O
Rendition	O
's	O
Vérité	O
1000	O
graphics	O
chip	O
(	O
VQuake	O
)	O
.	O
</s>
<s>
OpenGL	B-Application
support	O
was	O
added	O
in	O
the	O
form	O
of	O
the	O
GLQuake	O
executable	O
for	O
Windows	O
95	O
and	O
higher	O
.	O
</s>
<s>
Other	O
cards	O
capable	O
of	O
rendering	O
GLQuake	O
were	O
a	O
professional	O
(	O
and	O
very	O
expensive	O
)	O
Intergraph	O
3D	O
OpenGL	B-Application
card	O
and	O
later	O
,	O
the	O
PowerVR	B-Device
cards	O
.	O
</s>
<s>
To	O
optimize	O
the	O
software	O
rendering	O
engine	O
,	O
lightmaps	B-Data_Structure
were	O
shared	O
by	O
polygons	O
that	O
were	O
close	O
in	O
space	O
,	O
and	O
in	O
the	O
same	O
leaf	O
of	O
the	O
BSP	O
tree	O
.	O
</s>
<s>
This	O
means	O
that	O
quite	O
often	O
polygons	O
using	O
the	O
same	O
main	O
texture	O
could	O
not	O
be	O
rendered	O
at	O
the	O
same	O
time	O
with	O
the	O
3D	O
acceleration	O
,	O
due	O
to	O
the	O
multi-texturing	O
second	O
unit	O
having	O
to	O
be	O
reconfigured	O
with	O
another	O
lightmap	B-Data_Structure
.	O
</s>
<s>
This	O
architecture	O
decision	O
reduced	O
hardware-accelerated	B-General_Concept
rendering	O
performance	O
.	O
</s>
<s>
Quake	B-Application
includes	O
cooperative	O
and	O
deathmatch	O
multiplayer	O
modes	O
over	O
LAN	B-General_Concept
or	O
the	O
Internet	O
.	O
</s>
<s>
Quake	B-Application
uses	O
the	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
model	I-Operating_System
,	O
where	O
a	O
server	B-Application
has	O
control	O
of	O
all	O
game	O
events	O
.	O
</s>
<s>
All	O
players	O
connect	O
to	O
this	O
server	B-Application
in	O
order	O
to	O
participate	O
,	O
with	O
the	O
server	B-Application
telling	O
the	O
clients	O
what	O
is	O
happening	O
in	O
the	O
game	O
.	O
</s>
<s>
The	O
server	B-Application
may	O
either	O
be	O
a	O
dedicated	O
server	B-Application
or	O
a	O
Listen	B-Application
Server	I-Application
.	O
</s>
<s>
Even	O
in	O
the	O
latter	O
situation	O
,	O
Quake	B-Application
still	O
uses	O
the	O
client-server	B-Operating_System
model	I-Operating_System
,	O
as	O
opposed	O
to	O
the	O
peer-to-peer	O
networking	O
used	O
by	O
some	O
other	O
games	O
.	O
</s>
<s>
Quake	B-Application
thus	O
cannot	O
suffer	O
from	O
de-synchronized	O
network	O
games	O
that	O
could	O
occur	O
from	O
different	O
clients	O
disagreeing	O
with	O
each	O
other	O
,	O
since	O
the	O
server	B-Application
is	O
always	O
the	O
final	O
authority	O
.	O
</s>
<s>
On	O
December	O
21	O
,	O
1999	O
,	O
John	O
Carmack	O
of	O
id	O
Software	O
released	O
the	O
Quake	B-Application
engine	I-Application
source	O
code	O
on	O
the	O
Internet	O
under	O
the	O
terms	O
of	O
GPL-2.0-or-later	O
,	O
allowing	O
programmers	O
to	O
edit	O
the	O
engine	O
and	O
add	O
new	O
features	O
.	O
</s>
<s>
DarkPlaces	O
Engine	O
–	O
A	O
significantly	O
modified	O
engine	O
used	O
in	O
several	O
standalone	O
games	O
and	O
Quake	B-Application
mods	O
.	O
</s>
<s>
Although	O
the	O
last	O
stable	O
release	O
was	O
on	O
May	O
13	O
,	O
2014	O
,	O
it	O
has	O
received	O
numerous	O
updates	O
through	O
its	O
SVN	B-Application
repository	O
since	O
then	O
.	O
</s>
<s>
Its	O
home	O
page	O
was	O
hosted	O
on	O
Icculus.org	O
until	O
2021	O
,	O
when	O
the	O
engine	O
switched	O
to	O
a	O
Git	B-Application
repository	O
hosted	O
on	O
GitHub	B-Application
.	O
</s>
<s>
Team	B-Application
Xonotic	I-Application
provides	O
mirrors	O
of	O
DarkPlaces	O
source	O
code	O
on	O
various	O
social	O
coding	O
platforms	O
since	O
the	O
game	O
is	O
built	O
on	O
and	O
distributed	O
with	O
the	O
development	O
version	O
of	O
the	O
engine	O
.	O
</s>
<s>
GoldSrc	B-Application
–	O
The	O
first	O
engine	O
to	O
be	O
created	O
by	O
Valve	O
.	O
</s>
<s>
It	O
was	O
used	O
in	O
the	O
Half-Life	O
series	O
,	O
gave	O
rise	O
to	O
the	O
Source	B-Application
engine	I-Application
.	O
</s>
<s>
vkQuake	O
–	O
(	O
Derivative	O
of	O
Quakespasm	O
)	O
Uses	O
Vulkan	B-Application
API	I-Application
for	O
rendering	O
programmed	O
by	O
id	O
Software	O
employee	O
Axel	O
Gneiting	O
,	O
released	O
under	O
the	O
GPLv2	O
.	O
</s>
<s>
Year	O
Title	O
Developer(s )	O
Publisher(s )	O
1996	O
Quake	B-Application
id	O
Software	O
GT	O
Interactive	O
1997	O
Quake	B-Application
Mission	O
Pack	O
No	O
.	O
</s>
<s>
1	O
:	O
Scourge	O
of	O
Armagon	O
Hipnotic	O
Interactive	O
3D	O
Realms	O
Quake	B-Application
Mission	O
Pack	O
No	O
.	O
</s>
<s>
QuArK	B-Language
–	O
A	O
multipurpose	O
tool	O
for	O
Quake	O
engine-based	O
games	O
.	O
</s>
<s>
PakExpl	O
–	O
Used	O
for	O
opening	O
the	O
.pak	O
files	O
that	O
carry	O
Quake	B-Application
's	O
model	O
,	O
sound	O
,	O
and	O
level	O
data	O
,	O
as	O
well	O
as	O
the	O
progs.dat	O
file	O
.	O
</s>
<s>
qME	O
3.1	O
–	O
The	O
final	O
version	O
of	O
the	O
Quake	B-Application
model	O
editing	O
tool	O
,	O
can	O
be	O
used	O
to	O
convert	O
traditional	O
3d	O
model	O
files	O
into	O
Quake	B-Application
's	O
.mdl	O
format	O
.	O
</s>
<s>
qPAK	O
–	O
Another	O
tool	O
for	O
opening	O
Quake	B-Application
.pak	O
archives	O
.	O
</s>
