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Source engine

Following the release of Half-Life, more ambitious updates to the GoldSource engine were undertaken, and these updates eventually became the Source engine. Like the GoldSource engine, the Source engine received a number of major updates over its lifetime, but unlike the GoldSource engine, a number of the engine updates have remained in separate engine branches, rather than being integrated into a single base engine that all existing games and mods can take advantage of. It is written in C++.

Strata Source (formerly known as Chaos Engine) is a community updated Source engine branch by a team of Source engine license holders that have made numerous improvements to the engine.

Branch Games Features
Source 2004 Half-Life 2 Xbox .bsp v19
.mdl v44
.vtf v7.0
.vtf v7.1
Source 2006 .bsp v20
Alien Swarm Alien Swarm Vertex animation .vtf v7.5
Counter-Strike: Global Offensive Counter-Strike: Global Offensive Vertex animation .vtf v7.5
Dota 2 Dota 2 (Source 1) Vertex animation .bsp v22
.bsp v23

DirectX 8

The Source engine's renderer was largely developed using DirectX 8 as a number of error messages still refer to DirectX 8, for example Failed to lock index buffer in CMeshDX8::LockIndexBuffer and Failed to lock vertex buffer in CMeshDX8::LockVertexBuffer. It is not clear when the DirectX 8 renderer was replaced with DirectX 9.

DirectX 10

In 2008 Valve said that DirectX 9 was still sufficient (Lombardi, http://www.pcgameshardware.de/aid,643448/Interview/PCGH_interview_about_Left_4_Dead_part_2/&page=2Both). Dota 2 (Source 1) and Source Filmmaker shipped with a shaderapidx10.dll file but the Source engine was largely DirectX 9. The Source SDK also contains a dx10sdk directory.

DirectX 11

DirectX 11 support was never officially added to the Source engine by Valve, and was probably never experimented with: DirectX 10 support was explored but by the time DirectX 11 was released in 2009, Valve was likely already looking at the Source 2 engine. DirectX 11 support was added to Vindictus in 2021 (https://vindictus.nexon.net/news/68458/ver-2-79-update-note). Strata Source has also been updated to use DirectX 11 (https://wiki.stratasource.org/shared/).

DirectX 12

Valve's Source engine does not have DirectX 12 support but experimental DirectX 12 support was added to Respawn's Source engine in November 2022 (https://www.reddit.com/r/apexlegends/comments/yiek6d/dev_team_update_directx_12_beta_on_pcshare_your/).

OpenGL

The Source engine was only released with a DirectX renderer, but when the Source engine was ported to Linux and Mac, OpenGL support was added. The OpenGL support is by way of translating a subset of DirectX 9.0c calls and HLSL to their OpenGL 2 and GLSL equivalents. Valve's translation layer ToGL was open-sourced in 2014. Each Source engine game ships with a slightly different version of ToGL: not all updates were applied to all engine branches due to the difficulty of testing for regressions (Geldreich, https://richg42.blogspot.com/2014/03/togl-d3d9-opengl-layer-source-release.html).

Vulkan

In 2021 the Source engine received Vulkan support through dxvk (https://store.steampowered.com/oldnews/81067). The Vulkan support for Counter-Strike: Global Offensive was only for the Linux client however (https://blog.counter-strike.net/index.php/2021/12/36627/). In 2022 it was updated to use dxvk 2.0 (https://steamcommunity.com/games/portal2/announcements/detail/3488629295080243622). Strata Source has also been updated to use dxvk for Linux (https://wiki.stratasource.org/shared/)

Software renderer

Unlike the GoldSource engine, the Source engine did not have a software renderer - most likely the graphics were too advanced to be recreated without hardware acceleration. The Source 2004 and Source 2006 versions of studiomdl create .sw.vtx files which suggests that either a software renderer was planned or was carried over from the GoldSource engine far enough into development for traces to still show.

Shader model 3.0

Shader model 3.0 support was added to Xengine as part of Black Mesa development (https://chetanjags.wordpress.com/2022/06/01/blackmesa-xenengine-part1-a-heavily-modified-source-engine/).

Cascade Shadow Mapping

Cascade shadow mapping was added to the Counter-Strike: Global Offensive branch of the Source engine by Rich Geldreich (Geldreich, https://sites.google.com/site/richgel99/). It was also added to Xengine as part of Black Mesa development (https://store.steampowered.com/news/app/362890/view/4041374038285693825).

Screen-Space Ambient Occlusion

Screen-space ambient occlusion was added to the Dota 2 (Source 1) branch of the Source engine by Rich Geldreich (Geldreich, https://sites.google.com/site/richgel99/).

ScaleForm

VGUI2 was superceded by ScaleForm - ScaleForm was used by Valve in both Counter-Strike: Global Offensive and Dota 2 (Source 1) for the user interfaces and menus. Vindictus also replaced VGUI2 with ScaleForm.

Panorama

ScaleForm - a proprietary UI framework was superceded by Panorama. Originally built for the Source 2 engine, Panorama was added to Counter-Strike: Global Offensive on June 19th 2018 (https://blog.counter-strike.net/index.php/2018/06/20497/). Strata Source has also been updated to use Panorama (https://wiki.stratasource.org/shared/).

Qt

Source Filmmaker was built using Qt (https://codingrange.com/blog/retrospective-source-2-leaks-versus-reality). VGUI2 was superceded by Qt for the main menu in Xengine as part of Black Mesa development (https://chetanjags.wordpress.com/2023/07/11/blackmesa-xenengine-part2-how-a-frame-is-rendered/).

Speex

The Speex codec was reportedly used in Titanfall.

Wwise

Wwise audio was used in the Xbox 360 version of Titanfall (https://twitter.com/akmiked/status/1093533607963123714).

tier1

tier1 is Valve's Standard Template Library. It is high-performance alternative to the C++ Standard Template Library and its functionality is generally prefixed with CUtl.

VPhysics

The physics in the Source engine is powered by the Havok physics library, but there are a number of projects to replace Havok with different physics libraries. Gmod-vphysics was the first VPhysics replacement project and it used the Bullet physics library. source-sdk-bullet-physics was the second VPhysics replacement project and it used the Bullet physics library. VPhysics-Jolt is the third VPhysics replacement project and it uses the Jolt physics library.

64-bit support

Half-Life 2 and Half-Life 2: Lost Coast received experimental 64-bit support in late 2005 with assistance from AMD (https://store.steampowered.com/oldnews/496) but it was soon discontinued: the games were playable but there were various issues.

In May 2016, the Linux and Mac versions of Counter-Strike: Global Offensive were updated with 64-bit support, but only for the game clients - not the dedicated servers (https://blog.counter-strike.net/index.php/2016/05/14479/).

The Linux and Mac versions of Team Fortress 2 received experimental 64-bit support in January 2024 (although it had been hinted at since at least May 2023 (https://github.com/alliedmodders/hl2sdk/pull/127)), with Windows support planned at a later date. Experimental Windows support was released in February 2024 and in April 2024 Team Fortress 2 was updated with 64-bit support.

Besides Counter-Strike: Global Offensive and Team Fortress 2, Valve's Source engine has largely remained 32-bit, although the .vpc files in the Source SDK 2013 make mention of 64-bit support suggesting experiments at least as far back as 2013. Garry's Mod also has a 64-bit branch, as does Vindictus, and Respawn Entertainment's games Titanfall, Titanfall 2 and Apex Legends are all running exclusively on a 64-bit version of the Source engine. Strata Source has also been updated to have 64-bit support (https://wiki.stratasource.org/shared/).

Source 2 engine backports

Although the Source 2 engine has superceded the Source engine, a number of games still run on the Source engine and the Source 2 engine was likely in development while new Source engine games were being developed. Some features such as the Panorama UI were backported from the Source 2 engine to the Source engine.

List of games using the Source engine

Game Platform Developer Release date Play
Abatron Windows W3 Studios changed engines N/A
Alien Swarm Windows Black Cat Games
Valve Software
2010
Apex Legends Windows Respawn Entertainment 2019 https://www.ea.com/games/apex-legends/buy/pc
https://store.steampowered.com/app/1172470/Apex_Legends/
Xbox One https://www.microsoft.com/p/APEX-Legends/BV9ML45J2Q5V
Xbox Series X/S https://www.microsoft.com/p/APEX-Legends/BV9ML45J2Q5V
PlayStation 4
PlayStation 5
Nintendo Switch https://www.nintendo.com.au/games/nintendo-switch/apex-legends
Black Mesa Windows Crowbar Collective 2020
Blade Symphony Windows Puny Human 2014
Bloody Good Time Windows Outerlight 2010 https://store.steampowered.com/app/2450/Bloody_Good_Time/
Xbox 360 https://marketplace.xbox.com/en-us/product/bloody-good-time/66acd000-77fe-1000-9115-d802584109b3
CLANG Windows Subutai Corporation changed engines N/A
Codename Prime Windows Nigredo Studios unreleased N/A
CONSORTIUM Windows Interdimensional Games 2014
Contagion Windows Monochrome Games 2014
Counter-Strike: Source Windows Valve Software 2004
Counter-Strike: Global Offensive Windows Hidden Path Entertainment
Valve Software
2012 https://store.steampowered.com/app/730/CounterStrike_Global_Offensive/
Mac OS X https://store.steampowered.com/app/730/CounterStrike_Global_Offensive/
Linux https://store.steampowered.com/app/730/CounterStrike_Global_Offensive/
Xbox 360 https://marketplace.xbox.com/en-us/Product/Counter-Strike-GO/66acd000-77fe-1000-9115-d8025841125a
PlayStation 3
Counter-Strike: Online 2 Windows Nexon 2013
Cyber Diver arcade machine Taito 2009 physical media only
Dark Messiah of Might and Magic Windows Arkane Studios 2006
Dark Messiah of Might and Magic: Elements Xbox 360 Arkane Studios 2008 physical media only
Day of Defeat: Source Windows Valve Software 2005
Day of Infamy Windows New World Interactive 2017
Dear Esther Windows The Chinese Room 2021
Deep6 Windows Leaping Lizard Software not officially released
Dino D-Day Windows 800 North
Digital Ranch
2011
Dismounted Infantry Virtual Environment 2 Windows Maverick Developments
QinetiQ
2005
Divinia Chronicles: Relics of Gan-Ti Windows Team Monkey 2021
Dogfights Windows Kuma Reality Games 2007
Dota 2 Windows Valve Software 2013
Estranged: Act II Windows Alan Edwardes changed engines N/A
E.Y.E: Divine Cybermancy Windows Streum On Studio 2010
Faceless Windows Watchmaker changed engines N/A
Fairy Tale Busters Windows UtoPlanet 2017
Garry's Mod Windows Facepunch Studios 2006
G String Windows Eyaura 2020
Half-Life: Source Windows Valve Software 2004
Half-Life Deathmatch: Source Windows Valve Software 2006
Half-Life 2 Windows Valve Software 2004 https://store.steampowered.com/app/220/HalfLife_2/
Xbox 2005
Xbox 360 2007
PlayStation 3
Android nVidia Lightspeed Studios 2014 https://play.google.com/store/apps/details?id=com.nvidia.valvesoftware.halflife2
Half-Life 2: Lost Coast Windows Valve Software 2005
Half-Life 2: Episode One Windows Valve Software 2006 https://store.steampowered.com/app/380/HalfLife_2_Episode_One/
Xbox 360 2007
PlayStation 3
Android nVidia Lightspeed Studios 2014 https://play.google.com/store/apps/details?id=com.nvidia.valvesoftware.halflife2ep1
Half-Life 2: Episode Two Windows Valve Software 2007 https://store.steampowered.com/app/420/HalfLife_2_Episode_Two/
Xbox 360
PlayStation 3
Android nVidia Lightspeed Studios 2014 https://play.google.com/store/apps/details?id=com.nvidia.valvesoftware.halflife2ep2
Half-Life 2: Episode Three Windows Valve Software unreleased N/A
Half-Life 2: Deathmatch Windows Valve Software 2004
Half-Life 2: Survivor arcade machine Taito 2006 physical media only
HEAT REBORN Windows HEAT REBORN DEV TEAM 2021
Hybrid Xbox 360 5th Cell 2012 https://marketplace.xbox.com/en-us/product/hybrid/66acd000-77fe-1000-9115-d802584109e9
INFRA Windows Loiste Interactive 2016
Insurgency Windows New World Interactive 2014
I, Predator Windows Kuma Reality Games 2011
KUMA\WAR 2 Windows Kuma Reality Games 2006
Left 4 Dead Windows Valve Software 2008
Xbox 360
Left 4 Dead: Survivors arcade machine Taito 2014 physical media only
Left 4 Dead 2 Windows Valve Software 2009
Xbox 360
Military Conflict: Vietnam Windows Dustfade 2023
Mobsters Windows Kuma Reality Games 2007
National Blood Sport Windows LAN Clan
Kuma Reality Games
2010
Natural Selection 2 Windows Unknown Worlds Entertainment changed engines N/A
Nuclear Dawn Windows InterWave Studios 2011
Portal Windows Valve Software 2007 https://store.steampowered.com/app/400/Portal/
Xbox 360
PlayStation 3
Android nVidia Lightspeed Studios 2014 https://play.google.com/store/apps/details?id=com.nvidia.valvesoftware.portal
Nintendo Switch Valve Software 2022 https://www.nintendo.com/us/store/products/portal-companion-collection-switch/
Portal with RTX Windows nVidia Lightspeed Studios 2022 https://store.steampowered.com/app/2012840/Portal_with_RTX/
Portal: Still Alive Xbox 360 Valve Software 2008 https://marketplace.xbox.com/en-us/product/portal-still-alive/66acd000-77fe-1000-9115-d80258410960
Portal 2 Windows Valve Software 2011 https://store.steampowered.com/app/620/Portal_2/
Xbox 360
PlayStation 3
Nintendo Switch Valve Software 2022 https://www.nintendo.com/us/store/products/portal-companion-collection-switch/
Portal 2 Sixense MotionPack DLC Windows Sixense Studios 2011 https://store.steampowered.com/app/660/Portal_2_Sixense_MotionPack_DLC/
Portal 2 Sixense Perceptual Pack Windows Sixense Studios 2013 https://store.steampowered.com/app/247120/Portal_2_Sixense_Perceptual_Pack/
Postal III Windows Trashmasters
Running with Scissors
2011 https://store.steampowered.com/app/10220/Postal_III/
Xbox 360 not officially released N/A
PUNT Windows LunchHouse Software https://store.steampowered.com/app/507500/PUNT/
Return To Ravenholm Windows Arkane Studios unreleased N/A
Revelations 2012 Windows Dark Artz Entertainment 2012
Salvation Windows Black Wing Foundation changed engines N/A
SiN: Source Windows Ritual Entertainment not officially released
SiN Episodes: Emergence Windows Ritual Entertainment 2006
SiN Episodes 2 Windows Ritual Entertainment unreleased N/A
Stars of Blood Windows Valve Software unreleased N/A
Sting: The Secret Operations Windows YNK Games 2008
Street Soccer Windows Kuma Reality Games 2009
Tactical Intervention Windows FIX Korea 2013
Team Fortress 2: Invasion Windows Valve Software unreleased N/A
Team Fortress 2 Windows Valve Software 2007
Xbox 360
PlayStation 3
The Crossing Windows Arkane Studios unreleased N/A
The DinoHunters Windows Kuma Reality Games 2006
The Ship Windows Outerlight 2006
The Stanley Parable Windows Galactic Cafe 2013
The Undead Olympics Windows Outerlight unreleased N/A
They Hunger: Lost Souls Windows Black Widow Games not officially released N/A
Titanfall Windows Respawn Entertainment 2014
Xbox One
Xbox 360 BluePoint Games
Titanfall 2 Windows Respawn Entertainment 2016
Xbox One
PlayStation 4
Titanfall Online Windows Nexon 2016
Twilight War After The Fall Windows Smiling Gator Productions unreleased N/A
Vampire: The Masquerade - Bloodlines Windows Troika Games 2004
Velocity Brawl Windows Boolean Technologies changed engines N/A
Vindictus Windows Nexon
devCAT
2010
Whiskey Sour Windows Turtle Rock Studios unreleased
WWII Experience Windows Kuma Reality Games 2009
WWII\Vietnam Windows Kuma Reality Games 2006
Zeno Clash Windows ACE Team 2009
Zeno Clash: Ultimate Edition Xbox 360 ACE Team 2010 https://marketplace.xbox.com/en-US/Product/Zeno-Clash-UE/66acd000-77fe-1000-9115-d802584109dc

List of licensed mods using the Source engine

While Valve Software licensed the Source engine commercially, it also offered non-commercial licensing for mod creators (https://partner.steamgames.com/doc/sdk/uploading/distributing_source_engine): a number of stand-along free Source engine games and mods have been released on Steam. As a precursor, a number of mods were also released with a dependency on the Source SDK Base. There are also a number of tiles which are derivate of one of or more Valve Software's other titles.

Game Platform Developer Steam Release date Buy Type
Action: Source Windows Lights. Camera. Action! 2019 https://store.steampowered.com/app/977050/Action_Source/ stand-alone
Age of Chivalry Windows requires Source SDK Base 2006
AMYGDALA: Prelude Windows MOONLIT JOURNEYS 2024 stand-alone
Anarchy Arcade Windows
Battlegrounds III Windows The Battle Grounds Game Development Team
Bear Party: Adventure Windows Klems https://store.steampowered.com/app/1274450/ stand-alone
BrainBread 2 Windows
Codename CURE Windows
D.I.P.R.I.P. Warm Up Windows requires Source SDK Base 2006
Director's Cut Windows stand-alone
Double Action: Boogaloo Windows
Dystopia Windows Puny Human requires Source SDK Base 2006
Empires Windows requires Source SDK Base 2006
Estranged: Act I Windows Alan Edwardes requires Source SDK Base 2006
Eternal Silence Windows requires Source SDK Base 2006
Fistful of Frags Windows
From Earth Windows requires Half-Life 2
Infestus Windows
Insurgency: Modern Infantry Combat Windows New World Interactive requires Source SDK Base 2006
IOSoccer Windows
Jabroni Brawl: Episode 3 Windows
JBMod Windows requires Half-Life 2
Kreedz Climbing Windows
Momentum Mod Windows unreleased
Nightmare House: The Original Mod Windows We Create Stuff https://store.steampowered.com/app/2954780/Nightmare_House_The_Original_Mod/
No More Room in Hell Windows
Pirates, Vikings, & Knights II Windows
Ruby: Tunnel Vision Windows unreleased
Smashball Windows Smashball Labs LLC requires Source SDK Base 2006
Sven Co-op II Windows Sven Co-op Team unreleased
The Forgotten Ones Windows
Treason Windows Tomorrow Software
Vice and Virtue Windows Controlled Chaos Media unreleased https://store.steampowered.com/app/317340 unknown
Zombie Master: Reborn Windows ZM Reborn Team unreleased https://store.steampowered.com/app/813990 stand-alone
Zombie Panic! Source Windows