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Logo of Source Engine.
Screenshot in-game of Counter-Strike: Source Counter-Strike: Source, using the Source Engine.
Screenshot taken in-game of Counter-Strike: Global Offensive Counter-Strike: Global Offensive, which uses a newer branch of the Source Engine.

Source Source is a 3D game engine created by Valve, it is the successor to GoldSrc GoldSrc. Source has been used by Valve, third-party companies, and (much like GoldSource) countless community mods by people around the globe. Today, it is slowly being replaced by Source 2 Source 2 engine, but it's still being commonly used today.


Note.pngNote: Unofficially, some third-party games can also support Shader Model 5.0 and later by using DirectX 11 and later.
  • Bump mapping and Normal mapping on models and the world
  • Author shaders with HLSL
  • Cube and environment mapping
    • Cubemapping also supports Anisotropy (in all games since Counter-Strike: Global Offensive)
  • Phong shading for models
    • Phong is also supported on world brushes (in all games since Counter-Strike: Global Offensive)
  • Dynamic lights, vertex lighting and lightmaps, many light types including flickering, pulsing etc.
  • HDR (in all games since Source 2006) and SDR/LDR (not in Left 4 Dead 2 and later) lighting
  • Water with refraction, real-time world reflections and fresnel effects
  • Advanced particle systems that can emit sprites or models
  • Render-to-texture shadows allow for a large number of characters per scene
  • Occluder entities for visibility blocking
  • Indoor/Outdoor environments
    • Deformable terrain
    • 3D Skyboxes extend the horizon and add parallax on distant objects
    • Dynamically rendered organics (grass, trees, etc.)
  • Subdivision surfaces, diffuse & specular bump maps
  • Real-time radiosity lighting
  • Real-time cascaded shadow mapping that comes from the skybox (in all games since Counter-Strike: Global Offensive)
  • Effects include but are not limited to: particles, beams, volumetric smoke, sparks, blood, & environmental effects like fog and rain
  • Scalability
    • DX8-DX9 hardware supported (DX6-DX9 with modifications and fixed-function shaders)
Warning.pngWarning:DirectX 7 materials and earlier are no longer supported since Source 2007/Source 2009. Games that uses Left 4 Dead engine branch Left 4 Dead engine branch and later only support DirectX 9 materials.

Materials System

  • Instead of traditional textures, Source defines sets of materials that specify what the object is made from and the texture used for that object. A material specifies how an object will fracture when broken, what it will sound like when broken or dragged across another surface, and what that object's mass and buoyancy are. This system is much more flexible than other texture-only systems
  • Materials can interact with objects or NPCs, such as mud or ice for vehicles to slide/lose traction on

Multiplayer Network Code

  • Time- and gamer-tested by millions of gamers around the world
  • Support for both LAN-based multiplayer and Internet-based multiplayer games
  • Prediction analysis for interpolating collision/hit detection
  • Optimizations for high-latency, high-packet-loss 56k connections

Advanced Characters

  • Detailed and believable characters
  • Realistic eyes
    • Focus on player/object, not simply parallel views
    • Proper eye bulge for realistic eye reflections
  • Simulated musculature provides outstanding emotions, speech, and body language
  • Language independent speech, characters can speak naturally in many languages
  • Skeletal/bone system for animation
  • Layered animation system can synthesize complex animations out of several pieces


  • More responsive world with realistic interactions
  • Sounds & graphics follow from physics
  • AI characters can interact with physically simulated objects
  • Ropes/cables, machines, constraint systems, ragdoll physics
  • Can be controlled by level design
  • Kinematic animated bone followers
  • Custom procedural physics controllers
  • Vehicles
    • Wheels slip and skid
    • Realistic suspensions with springs on each wheel
    • Realistic leaning during acceleration/deceleration and turning
    • Individually tunable parameters such as horsepower, gearing, max speed, shift speed, tire material, tire friction, spring tension/dampening, etc.
    • Multiple players in a vehicle in multiplayer
    • Hovercraft support for cheaper simulation

Advanced AI

  • I/O system allows level designers to control AI
  • Sophisticated navigation: characters that run, fly, jump, crouch, climb stairs and ladders, and burrow underground
  • AI senses things using sight, sound, and smell
  • AI relationships determine friend/foe status of other entities
  • Battle AI allows squads of AI characters to operate together, know when to advance, retreat, lay cover fire, etc.

Sound System

  • 7.1, 5.1 surround sound, 4 speaker surround
Bug.pngBug:On system running Windows Vista and later, due to the game engine using DirectSound and older version of Miles Sound System, the game may output only 5.1 surround despite 7.1 selected or 7.1 audio may not work properly without custom dsound.dll (such as Creative Alchemy, DSOAL or IndirectSound).
Note.pngNote: Some Source games (such as Alien Swarm Alien Swarm, Portal 2 Portal 2 and Counter-Strike: Global Offensive Counter-Strike: Global Offensive) may not include options to enable 7.1 surround sound without using console commands.
  • High-quality 3D spatialization
  • Custom software DSP
  • Automatic DSP based on environmental geometry
  • Microsoft ADPCM-compressed WAV files
  • 16-bit 44.1 KHz (CD Quality), stereo wave data with all features
Warning.pngWarning:48 KHz audio (DVD Quality) is not supported.
  • MP3 decompression (requires Miles license)
  • Support for audio streaming on any wave [Clarify]
  • Real-time wave file stitching [Clarify]
  • Pre-authored Doppler effect encoded waves
  • Pre-authored distance variant encoded waves
  • Commentary system


  • Server browser — Displays all active game servers and allows a player to choose which one to participate on. Players can filter and sort server lists in order to speed up the display and selection of a server.
  • VGUI — Valve's custom GUI interface mimics most of the Windows controls but is rendered using the Source engine for both in game and out of game uniform UI display. Some features:
    • Dynamic in-game HUD display
    • Many widgets/controls (e.g., buttons, treeview, html control…)
    • Themes/custom visualization allowed
    • Platform independent
    • Localized text (Unicode compliant)


  • All code written in C/C++ using Visual Studio .NET 2003 and later. Easily and quickly derive new entities from existing base classes
  • Internal context sensitive performance monitoring system
  • Graphics performance measurement tools built into the engine
  • Modular code design (via DLLs) allows swapping out of core components for easy upgrading or code replacement
  • VScript scripting system allows using external coding languages, such as Squirrel and Lua, in maps to create more complex systems (in all games since Left 4 Dead 2) (also in Team Fortress 2)


  • HLFaceposer HLFaceposer
    • Facial expression tool used to craft speech and emotions
  • Hammer Valve Hammer Editor
    • WYSIWYG World editor
    • Create world brushes
    • Terrain editor
    • Place detailed world models and AI NPCs
    • Set navigation points/paths for NPCs
    • Place triggers, clip brushes, logic, etc.
    • Allows level designer to hook up I/O between entities to control AI within the game
  • HLMV Half-Life Model Viewer
    • Full model previewer
    • Rotate models in any direction
    • Set up hit boxes
    • View physics hull
    • View normals
    • Wireframe, shaded or textured view modes
  • Studiomdl
    • Model compiler
    • Map compilation tools (bsp, lighting and visibility)
    • VMPI — distributed compilation tool allowing level compiles to be spread across many PCs greatly reducing compile times
  • Exporters
    • XSI, Max and Maya .smd exporters for exporting 3D models

Games on Source


Games made by Valve.


Games and mods made by third-party companies and mod teams.



This section are for unreleased 3rd party games that are not publicly released or is in Beta/Early Access.

More Third-party Source Engine games

See Also