Alien Swarm engine branch
The 
Alien Swarm engine branch was released in 2010 with Alien Swarm. It succeeds the 
Left 4 Dead engine branch and precedes the 
Portal 2 engine branch.[1] This branch is the only Source engine branches (post-Orange Box) that have officially available source code, with all the new features introduced in Left 4 Dead engine branch (BSP 21, Swaying trees, VScript, Water flow maps), aswell as VTF 7.5 and other mentioned below which are later used in Portal 2 and Counter-Strike: Global Offensive. Some of these features however, are later backported to Orange Box-derived branch, under Team Fortress 2 branch.
Features
New since Left 4 Dead engine branch is:
- TileGen
- A new quick-build mapping tool. Level designers create connectible rooms and corridors which can be arranged either by hand or programmatically. TileGen maps can be played in-editor, and/or can be exported to Hammer for further refinement.illuminate an entire scene.
- VTF version 7.5 and PCF version Binary 5 PCF 2
- The latest versions of Source's texture and particle formats.
- Depth of field
- A real-time depth of field shader blurs backdrop scenery.
- Vertex animation
- The ability to animate vertexes directly is now supported.
- Various entity improvements
- Numerous entities have been improved and have new features, such as env_fire and env_projectedtexture.
- Water debris flow
- Water now supports the ability to use a base texture layer that is flowed using a flow map. This implemention is less advanced than Portal 2's, however.
- Lightmap influence on cubemapped materials
- Lightmaps can now tint cubemap reflections in the LightmappedGeneric shader.
Availability and usage
Gamecode for this branch is included in the {{Game link}} is deprecated. Use {{Software}} instead.
.
- 2010 Alien Swarm
- 2012
Alien Swarm Deferred - 2012
Source Filmmaker - 2014
Lambda Wars - 2017
Alien Swarm: Reactive Drop
