Volumetric lighting

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Volumetric lighting is a lighting technique meant to simulate light bouncing off fog or dust particles in the air, such as a warehouse or foggy beach. It makes the player see beams of light shining from the sun or other light sources. Currently, the only Valve-made software running on Source that supports Volumetric Lighting is Source Filmmaker, however some third-party engines incorporate volumetric lighting into env_projectedtexture. If the game you are making maps for doesn't support volumetric lighting, you can use some workarounds seen here.

Most versions of Source 2 have support for Volumetric lighting by default

Media

Volumetric lighting in Source Filmmaker

Volumetric lighting in Alien Swarm Deferred

Volumetric lighting in Portal 2: Desolation

Volumetric lighting in Half Life Alyx

Volumetric lighting in Portal 2: Community Edition

Native Support

Source

Game	Supports
Source 2004 Source 2006 Source 2007 Source 2009/ Source Multiplayer Source 2013 Half-Life: Source Day of Defeat: Source Half-Life 2 Half-Life 2: Episode One Half-Life 2: Episode Two Alien Swarm Alien Swarm: Reactive Drop Half-Life Deathmatch: Source Half-Life 2: Deathmatch Half-Life 2: Lost Coast Counter-Strike: Source Team Fortress 2 Portal Left 4 Dead Left 4 Dead 2 Portal 2 Black Mesa	NO
Alien Swarm Deferred Apex Legends Portal 2: Desolation	YES
Source Filmmaker Strata Source	YES (`env_projectedtexture`)