<s>
It	O
debuted	O
as	O
the	O
successor	O
to	O
GoldSrc	B-Application
in	O
2004	O
with	O
the	O
releases	O
of	O
Half-Life	B-Application
:	O
Source	O
,	O
Counter-Strike	B-Application
:	I-Application
Source	I-Application
,	O
and	O
Half-Life	B-Application
2	I-Application
.	O
</s>
<s>
Updates	O
to	O
Source	O
were	O
released	O
in	O
incremental	O
versions	O
,	O
with	O
the	O
engine	O
being	O
succeeded	O
by	O
Source	B-Operating_System
2	I-Operating_System
by	O
the	O
late	O
2010s	O
.	O
</s>
<s>
Source	O
distantly	O
originates	O
from	O
the	O
GoldSrc	B-Application
engine	I-Application
,	O
itself	O
a	O
heavily	O
modified	O
version	O
of	O
John	O
Carmack	O
's	O
Quake	B-Application
engine	I-Application
with	O
some	O
code	O
from	O
the	O
Quake	B-Application
II	I-Application
engine	I-Application
.	O
</s>
<s>
Carmack	O
commented	O
on	O
his	O
blog	O
in	O
2004	O
that	O
"	O
there	O
are	O
still	O
bits	O
of	O
early	O
Quake	B-Application
code	O
in	O
Half-Life	B-Application
2	I-Application
"	O
.	O
</s>
<s>
Source	O
was	O
developed	O
part-by-part	O
from	O
this	O
fork	B-Application
onwards	O
,	O
slowly	O
replacing	O
GoldSrc	B-Application
in	O
Valve	O
's	O
internal	O
projects	O
and	O
,	O
in	O
part	O
,	O
explaining	O
the	O
reasons	O
behind	O
its	O
unusually	O
modular	O
nature	O
.	O
</s>
<s>
Valve	O
's	O
development	O
of	O
Source	O
since	O
has	O
been	O
a	O
mixture	O
of	O
licensed	O
middleware	B-General_Concept
and	O
in-house-developed	O
code	O
.	O
</s>
<s>
Among	O
others	O
,	O
Source	O
uses	O
Bink	B-Algorithm
Video	I-Algorithm
for	O
video	O
playback	O
.	O
</s>
<s>
With	O
Steam	B-Application
,	O
Valve	O
can	O
distribute	O
these	O
updates	O
automatically	O
among	O
its	O
many	O
users	O
.	O
</s>
<s>
The	O
release	O
of	O
Half-Life	B-Application
2	I-Application
:	I-Application
Episode	I-Application
One	I-Application
and	O
The	B-Application
Orange	I-Application
Box	I-Application
both	O
introduced	O
new	O
versions	O
of	O
the	O
engine	O
that	O
could	O
not	O
be	O
used	O
to	O
run	O
older	O
games	O
or	O
mods	O
without	O
the	O
developers	O
performing	O
upgrades	O
to	O
code	O
and	O
,	O
in	O
some	O
cases	O
,	O
content	O
.	O
</s>
<s>
The	O
Source	O
2006	O
branch	O
was	O
the	O
term	O
used	O
for	O
Valve	O
's	O
games	O
using	O
technology	O
that	O
culminated	O
with	O
the	O
release	O
of	O
Half-Life	B-Application
2	I-Application
:	I-Application
Episode	I-Application
One	I-Application
.	O
</s>
<s>
HDR	B-Device
rendering	I-Device
and	O
color	O
correction	O
were	O
first	O
implemented	O
in	O
2005	O
using	O
Day	B-Application
of	I-Application
Defeat	I-Application
:	I-Application
Source	I-Application
,	O
which	O
required	O
the	O
engine	O
's	O
shaders	O
to	O
be	O
rewritten	O
.	O
</s>
<s>
The	O
former	O
,	O
along	O
with	O
developer	O
commentary	O
tracks	O
,	O
were	O
showcased	O
in	O
Half-Life	B-Application
2	I-Application
:	I-Application
Lost	I-Application
Coast	I-Application
.	O
</s>
<s>
Image-based	B-Algorithm
rendering	I-Algorithm
technology	O
had	O
been	O
in	O
development	O
for	O
Half-Life	B-Application
2	I-Application
,	O
but	O
was	O
cut	O
from	O
the	O
engine	O
before	O
its	O
release	O
.	O
</s>
<s>
It	O
was	O
mentioned	O
again	O
by	O
Gabe	O
Newell	O
in	O
2006	O
as	O
a	O
piece	O
of	O
technology	O
he	O
would	O
like	O
to	O
add	O
to	O
Source	O
to	O
implement	O
support	O
for	O
much	O
larger	O
scenes	O
that	O
are	O
impossible	O
with	O
strictly	O
polygonal	B-General_Concept
objects	O
.	O
</s>
<s>
The	O
Source	O
2007	O
branch	O
represented	O
a	O
full	O
upgrade	O
of	O
the	O
Source	B-Application
engine	I-Application
for	O
the	O
release	O
of	O
The	B-Application
Orange	I-Application
Box	I-Application
.	O
</s>
<s>
An	O
in-process	O
tools	O
framework	O
was	O
created	O
to	O
support	O
it	O
,	O
which	O
also	O
supported	O
the	O
initial	O
builds	O
of	O
Source	B-Language
Filmmaker	I-Language
.	O
</s>
<s>
The	O
release	O
of	O
The	B-Application
Orange	I-Application
Box	I-Application
on	O
multiple	O
platforms	O
allowed	O
for	O
a	O
large	O
code	O
refactoring	O
,	O
which	O
let	O
the	O
Source	B-Application
engine	I-Application
take	O
advantage	O
of	O
multiple	O
CPU	O
cores	O
.	O
</s>
<s>
However	O
,	O
support	O
on	O
the	O
PC	O
was	O
experimental	O
and	O
unstable	O
until	O
the	O
release	O
of	O
Left	B-Application
4	I-Application
Dead	I-Application
.	O
</s>
<s>
Multiprocessor	O
support	O
was	O
later	O
backported	O
to	O
Team	B-Application
Fortress	I-Application
2	I-Application
and	O
Day	B-Application
of	I-Application
Defeat	I-Application
:	I-Application
Source	I-Application
.	O
</s>
<s>
Valve	O
created	O
the	B-Operating_System
Xbox	I-Operating_System
360	I-Operating_System
release	O
of	O
The	B-Application
Orange	I-Application
Box	I-Application
in-house	O
,	O
and	O
support	O
for	O
the	O
console	O
is	O
fully	O
integrated	O
into	O
the	O
main	O
engine	O
codeline	O
.	O
</s>
<s>
It	O
includes	O
asset	O
converters	O
,	O
cross-platform	O
play	O
and	O
Xbox	B-Application
Live	I-Application
integration	O
.	O
</s>
<s>
Program	O
code	O
can	O
be	O
ported	O
from	O
PC	O
to	O
Xbox	B-Operating_System
360	I-Operating_System
simply	O
by	O
recompiling	O
it	O
.	O
</s>
<s>
The	O
PlayStation	B-Operating_System
3	I-Operating_System
release	O
was	O
outsourced	O
to	O
Electronic	O
Arts	O
,	O
and	O
was	O
plagued	O
with	O
issues	O
throughout	O
the	O
process	B-Operating_System
.	O
</s>
<s>
Gabe	O
Newell	O
cited	O
these	O
issues	O
when	O
criticizing	O
the	O
console	O
during	O
the	O
release	O
of	O
The	B-Application
Orange	I-Application
Box	I-Application
.	O
</s>
<s>
The	O
Left	B-Application
4	I-Application
Dead	I-Application
branch	O
is	O
an	O
overhaul	O
of	O
many	O
aspects	O
of	O
the	O
Source	B-Application
engine	I-Application
through	O
the	O
development	O
of	O
the	O
Left	B-Application
4	I-Application
Dead	I-Application
series	O
.	O
</s>
<s>
Multiprocessor	O
support	O
was	O
further	O
expanded	O
,	O
allowing	O
for	O
features	O
like	O
split	O
screen	O
multiplayer	O
,	O
additional	O
post-processing	O
effects	O
,	O
event	O
scripting	O
with	O
Squirrel	B-Language
,	O
and	O
the	O
highly-dynamic	O
AI	O
Director	O
.	O
</s>
<s>
This	O
branch	O
later	O
fueled	O
the	O
releases	O
of	O
Alien	B-Application
Swarm	I-Application
and	O
Portal	B-Application
2	I-Application
,	O
the	O
former	O
released	O
with	O
source	O
code	O
outlining	O
many	O
of	O
the	O
changes	O
made	O
since	O
the	O
branch	O
began	O
.	O
</s>
<s>
Portal	B-Application
2	I-Application
,	O
in	O
addition	O
,	O
served	O
as	O
the	O
result	O
of	O
Valve	O
taking	O
the	O
problem	O
of	O
porting	O
to	O
PlayStation	B-Operating_System
3	I-Operating_System
in-house	O
,	O
and	O
in	O
combination	O
with	O
Steamworks	O
integration	O
creating	O
what	O
they	O
called	O
"	O
the	O
best	O
console	O
version	O
of	O
the	O
game	O
"	O
.	O
</s>
<s>
In	O
April	O
2010	O
,	O
Valve	O
released	O
all	O
of	O
their	O
major	O
Source	O
games	O
on	O
OS	B-Operating_System
X	I-Operating_System
,	O
coinciding	O
with	O
the	O
release	O
of	O
the	O
Steam	B-Application
client	I-Application
on	O
the	O
same	O
platform	O
.	O
</s>
<s>
The	O
first	O
of	O
Valve	O
's	O
games	O
to	O
support	O
Linux	O
was	O
Team	B-Application
Fortress	I-Application
2	I-Application
,	O
the	O
port	O
released	O
in	O
October	O
2012	O
along	O
with	O
the	O
closed	O
beta	O
of	O
the	O
Linux	O
version	O
of	O
Steam	B-Application
.	O
</s>
<s>
Both	O
the	O
OS	B-Operating_System
X	I-Operating_System
and	O
Linux	O
ports	O
of	O
the	O
engine	O
take	O
advantage	O
of	O
OpenGL	B-Application
and	O
are	O
powered	O
by	O
Simple	B-Operating_System
DirectMedia	I-Operating_System
Layer	I-Operating_System
.	O
</s>
<s>
During	O
the	O
process	B-Operating_System
of	O
porting	O
,	O
Valve	O
rearranged	O
most	O
of	O
the	O
games	O
released	O
up	O
to	O
The	B-Application
Orange	I-Application
Box	I-Application
into	O
separate	O
,	O
but	O
parallel	O
"	O
singleplayer	O
"	O
and	O
"	O
multiplayer	O
"	O
branches	O
.	O
</s>
<s>
Support	O
for	O
Valve	O
's	O
internal	O
Steam	B-Application
Pipe	O
distribution	O
system	O
as	O
well	O
as	O
the	O
Oculus	B-Device
Rift	I-Device
are	O
included	O
.	O
</s>
<s>
In	O
May	O
2014	O
,	O
Nvidia	O
released	O
ports	O
of	O
Portal	B-Application
and	O
Half-Life	B-Application
2	I-Application
to	O
their	O
Tegra	O
4-based	O
Android	O
handheld	B-Application
game	I-Application
console	I-Application
Nvidia	B-Application
Shield	I-Application
.	O
</s>
<s>
Source	O
SDK	O
is	O
the	O
software	B-Application
development	I-Application
kit	I-Application
for	O
the	O
Source	B-Application
engine	I-Application
,	O
and	O
contains	O
many	O
of	O
the	O
tools	O
used	O
by	O
Valve	O
to	O
develop	O
assets	O
for	O
their	O
games	O
.	O
</s>
<s>
Source	O
SDK	O
was	O
launched	O
as	O
a	O
free	O
standalone	O
toolset	O
through	O
Steam	B-Application
,	O
and	O
required	O
a	O
Source	O
game	O
to	O
be	O
purchased	O
on	O
the	O
same	O
account	O
.	O
</s>
<s>
Since	O
the	O
release	O
of	O
Left	B-Application
4	I-Application
Dead	I-Application
in	O
late	O
2008	O
,	O
Valve	O
began	O
releasing	O
"	O
Authoring	O
Tools	O
"	O
for	O
individual	O
games	O
,	O
which	O
constitute	O
the	O
same	O
programs	O
adapted	O
for	O
each	O
game	O
's	O
engine	O
build	O
.	O
</s>
<s>
After	O
Team	B-Application
Fortress	I-Application
2	I-Application
became	O
free-to-play	O
,	O
Source	O
SDK	O
was	O
effectively	O
made	O
open	O
to	O
all	O
Steam	B-Application
users	O
.	O
</s>
<s>
Level	O
geometry	O
is	O
created	O
with	O
3D	O
polygons	B-General_Concept
called	O
brushes	B-Application
;	O
each	O
face	O
can	O
be	O
assigned	O
a	O
texture	O
which	O
also	O
defines	O
the	O
properties	O
of	O
the	O
surface	O
such	O
as	O
the	O
sounds	O
used	O
for	O
footsteps	O
.	O
</s>
<s>
The	O
editor	O
also	O
features	O
an	O
in-depth	O
logic	O
I/O	B-General_Concept
system	O
that	O
can	O
be	O
used	O
to	O
create	O
complex	O
interactive	O
elements	O
.	O
</s>
<s>
Signals	O
to	O
trigger	O
different	O
responses	O
or	O
change	O
the	O
state	O
of	O
an	O
entity	O
can	O
be	O
sent	O
between	O
entities	O
such	O
as	O
buttons	O
,	O
NPCs	O
,	O
intangible	O
trigger	O
brushes	B-Application
,	O
and	O
map	O
props	O
.	O
</s>
<s>
The	O
Source	O
Dedicated	O
Server	O
(	O
SRCDS	O
)	O
is	O
a	O
standalone	O
launcher	O
for	O
the	O
Source	B-Application
engine	I-Application
that	O
runs	O
multiplayer	O
game	O
sessions	O
without	O
requiring	O
a	O
client	O
.	O
</s>
<s>
The	O
Source	B-Language
Filmmaker	I-Language
(	O
SFM	B-Language
)	O
is	O
a	O
video	O
capture	O
and	O
editing	O
application	O
that	O
works	O
from	O
within	O
the	O
Source	B-Application
engine	I-Application
.	O
</s>
<s>
Developed	O
by	O
Valve	O
,	O
the	O
tool	O
was	O
originally	O
used	O
to	O
create	O
movies	O
for	O
Day	B-Application
of	I-Application
Defeat	I-Application
:	I-Application
Source	I-Application
and	O
Team	B-Application
Fortress	I-Application
2	I-Application
.	O
</s>
<s>
It	O
was	O
also	O
used	O
to	O
create	O
some	O
trailers	O
for	O
Source	B-Application
Engine	I-Application
games	O
.	O
</s>
<s>
In	O
June	O
2016	O
,	O
Valve	O
released	O
the	O
Destinations	O
Workshop	O
Tools	O
,	O
a	O
set	O
of	O
free	O
virtual	B-Application
reality	I-Application
(	O
VR	O
)	O
creation	O
tools	O
running	O
using	O
the	O
Source	B-Operating_System
2	I-Operating_System
SDK	O
.	O
</s>
<s>
In	O
June	O
2005	O
,	O
Valve	O
opened	O
the	O
Valve	O
Developer	O
Community	O
(	O
VDC	O
)	O
wiki	B-Protocol
.	O
</s>
<s>
VDC	O
replaced	O
Valve	O
's	O
static	O
Source	O
SDK	O
documentation	O
with	O
a	O
full	O
MediaWiki-powered	O
community	O
site	O
.	O
</s>
<s>
Valve	O
staff	O
have	O
occasionally	O
produced	O
professional	O
and/or	O
academic	O
papers	O
for	O
various	O
events	O
and	O
publications	O
,	O
including	O
SIGGRAPH	O
,	O
Game	O
Developer	O
Magazine	O
and	O
Game	O
Developers	O
Conference	O
,	O
explaining	O
various	O
aspects	O
of	O
Source	B-Application
engine	I-Application
's	O
development	O
.	O
</s>
<s>
+	O
List	O
of	O
games	O
using	O
SourceYearTitleDeveloper(s )	O
Publisher(s )	O
2004	O
Counter-Strike	B-Application
:	I-Application
Source	I-Application
Valve	O
Valve	O
Half-Life	B-Application
2Vampire	O
:	O
The	O
Masquerade	O
–	O
Bloodlines	B-Application
Troika	O
Games	O
Activision	O
Half-Life	B-Application
2	I-Application
:	O
DeathmatchValve	O
Valve	O
Half-Life	B-Application
:	O
Source	O
2005	O
Day	B-Application
of	I-Application
Defeat	I-Application
:	I-Application
Source	I-Application
Half-Life	B-Application
2	I-Application
:	I-Application
Lost	I-Application
Coast	I-Application
2006	O
Half-Life	B-Application
Deathmatch	O
:	O
Source	O
Half-Life	B-Application
2	I-Application
:	O
Episode	O
OneGarry	O
's	O
ModFacepunch	O
StudiosSiN	O
EpisodesRitual	O
EntertainmentRitual	O
EntertainmentDark	O
Messiah	O
of	O
Might	O
and	O
MagicArkane	O
StudiosUbisoftThe	O
Ship	O
Outerlight	O
Mindscape	O
(	O
EU	O
)	O
,	O
Merscom	O
(	O
NA	O
)	O
Kuma	B-Application
\War	I-Application
Kuma	O
Reality	O
GamesKuma	O
Reality	O
Games	O
2007	O
Half-Life	B-Application
2	I-Application
:	O
Episode	O
TwoValve	O
Valve	O
Team	B-Application
Fortress	I-Application
2	I-Application
PortalDystopia	O
Team	O
Dystopia	B-Application
,	O
Puny	O
Human	O
Puny	O
HumanInsurgency	O
:	O
Modern	O
Infantry	O
Combat	O
Insurgency	B-Application
Development	O
Team	O
New	O
World	O
Interactive	O
2008	O
Left	O
4	O
DeadValve	O
Valve	O
2009	O
Left	B-Application
4	I-Application
Dead	I-Application
2Zeno	O
Clash	O
ACE	O
Team	O
Iceberg	O
Interactive	O
,	O
Tripwire	O
InteractiveNeoTokyo	O
Studio	O
Radi-8	O
NEOTOKYO	B-Application
2010Bloody	O
Good	O
Time	O
Outerlight	O
UbisoftVindictus	O
devCAT	O
NexonE.Y.E.	O
</s>
<s>
Titanfall	B-Application
,	O
Titanfall	B-Application
2	I-Application
,	O
and	O
Apex	B-Application
Legends	I-Application
are	O
not	O
included	O
because	O
their	O
engines	O
,	O
while	O
originally	O
based	O
on	O
the	O
Source	O
SDK	O
,	O
were	O
modified	O
to	O
the	O
point	O
that	O
they	O
are	O
effectively	O
different	O
engines	O
.	O
</s>
<s>
A	O
successor	O
to	O
Source	O
,	O
Source	B-Operating_System
2	I-Operating_System
,	O
was	O
announced	O
by	O
Valve	O
at	O
the	O
Game	O
Developers	O
Conference	O
in	O
March	O
2015	O
.	O
</s>
<s>
There	O
,	O
Valve	O
stated	O
that	O
it	O
would	O
be	O
free	O
to	O
use	O
for	O
developers	O
,	O
with	O
support	O
for	O
the	O
Vulkan	B-Application
graphical	I-Application
API	I-Application
,	O
as	O
well	O
as	O
using	O
a	O
new	O
in-house	O
physics	O
engine	O
called	O
Rubikon	O
.	O
</s>
<s>
In	O
June	O
2015	O
,	O
Valve	O
announced	O
that	O
Dota	B-Application
2	I-Application
,	O
originally	O
made	O
in	O
the	O
Source	B-Application
engine	I-Application
,	O
would	O
be	O
ported	O
over	O
to	O
Source	B-Operating_System
2	I-Operating_System
in	O
an	O
update	O
called	O
Dota	B-Application
2	I-Application
Reborn	O
.	O
</s>
