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.
Engine branches
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 | |||
| 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 | |||
| 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 | |||
| 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/ |
| 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/ |
| 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 | |
| Left 4 Dead: Survivors | arcade machine | Taito | 2014 | physical media only |
| Left 4 Dead 2 | Windows | Valve Software | 2009 | |
| 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/420/HalfLife_2_Episode_Two/ |
| 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.au/games/nintendo-switch/portal-companion-collection | |
| 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/ |
| Nintendo Switch | Valve Software | 2022 | https://www.nintendo.com.au/games/nintendo-switch/portal-companion-collection | |
| 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 |
| 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 | |
| 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 | ||||
| Bear Party: Adventure | Windows | Klems | https://store.steampowered.com/app/1274450/ | standalone | |
| BrainBread 2 | Windows | ||||
| Codename CURE | Windows | ||||
| D.I.P.R.I.P. Warm Up | Windows | requires Source SDK Base 2006 | |||
| Director's Cut | Windows | standalone | |||
| 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 | |||
| 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 |