This article relates to the game "Left 4 Dead". Click here for more information.
This article relates to the game "Left 4 Dead 2". Click here for more information.
This article's documentation is for anything that uses the Source engine. Click here for more information.

Left 4 Dead engine branch

From Valve Developer Community
Jump to: navigation, search

English (en)中文 (zh)

The Left 4 Dead engine branch Left 4 Dead engine branch was released in 2008 with Left 4 Dead Left 4 Dead and continued in 2009 with Left 4 Dead 2 Left 4 Dead 2. It was maintained side-by-side with the Source 2007 & Source 2009 Orange Box branches but was ultimately discontinued with the release of the Alien Swarm engine branch Alien Swarm engine branch, being the successor of this branch. However, as of 2024, this branch is still being actively updated in order to fix security issues and other bugs, aswell as adding new contents (such as Left 4 Dead 2 Left 4 Dead 2's Last Stand update back in 2021).

Unlike other branches (with the exception of some third-party games), L4D (and later branches) does not require earlier versions of Source to be installed or bundled with Half-Life 2 content in order to run. It stands entirely alone.


New since the Source 2007 Orange Box engine branch is:

VPK files and add-ons
A new archive format for easy content distribution, replacing the old GCF format used in Source 2009 Source 2009 and earlier. VPK was later eventually backported to previous branch during the transition to the new SteamPipe content distribution system.
NextBot AI
Source's original AI routines appear to have been completely replaced by the NextBot, the successor to Mike Booth's Counter-Strike bot. As well as unknown changes to code structure, the old nodegraph system has been superseded by polygonal navigation meshes that are automatically generated by the engine.
AI director
A "gamemaster" for the entire game which controls NPC spawning, music, weather effects, map layout, and more.
Rewritten speech response system
The speech response system has been rewritten, with several new features and improved performance. Details here and here.
Up to four players can play on the same screen at once.
Subtitles for intro movies and other Bink-based videos
Allows subtitles (including custom ones) to be put on timelines for when they should show.
Lag compensated props
prop_physics entities can be selectively lag compensated.
Shader and effect detail options
New options that allow for better performance on low-end machines, entirely replacing the old DirectX level system.
New post-processing effects
More post-processing effects have been added, such as film grain and vignette.
Radial fog and fog volumes
Radial fog replaces the previous planar-based fog, and multiple fog controllers can now be used within defined volumes.
Local light shadows
Render-to-texture shadows can now be calculated per-entity, and their direction determined by the closest light source.
Swaying trees
A material parameter that gives the effect of trees swaying in the wind.
Per-texel color tint masking for models
Models can now use the alpha channel of their base textures to define areas to tint with a specific color.
VScript (in all games since Left 4 Dead 2)
A powerful new scripting system primarily using Squirrel Squirrel.
Water flow maps (in all games since Left 4 Dead 2)
Water can now flow using flow maps, and water fog can now receive lightmaps.


Source code for this branch is not publicly available. However, server plugins are possible, and authoring tools exist for custom content.