Volumetric lighting

Volumetric fog 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 fog is Source Filmmaker, however some third-party engines incorporate Volumetric fog into env_projectedtexture. If the game you are making maps for doesn't support Volumetric fog, you can use some workarounds seen here.

Most Source 2 games have support for Volumetric fog by default.

Media

Volumetric fog in Source Filmmaker

Volumetric fog in Alien Swarm Deferred

Volumetric fog in Portal 2: Desolation

Volumetric fog in Half Life Alyx

Volumetric fog 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)

Source 2

Game	Supports
Half-Life: Alyx	Yes
Counter-Strike 2	Yes
S&box	Yes

Using models/textures to fake Volumetric fog

	Using vollight_stainedglass.mdl		Model in Hammer	Model in engine

	Using vol_light128x128.mdl		Model in Hammer	Model in engine

Note:On DirectX 9, Volumetric fog on Old Engine was slightly less visible compared to using DX8 level. However, the Volumetric fog on New Engine DX9 was even less visible (or nearly invisible) compared to Old Engine's DX9. This is likely due to a bug (or changes to the lighting) on Source 2007 and later.^[1][2]

	Old Engine	New Engine (Source 2013)
DirectX 8.1 (and earlier)
DirectX 9.0+

References

References

1. Jasper Carmack (@JasperCarmack) (April 3, 2024). "Comparing the differences between Half-Life 2 (Legacy / "DX8" shaders) on the left and (Modern) DX9+ shaders on the right.".  X (Twitter). Retrieved September 14, 2025.. 2. Jasper Carmack (@JasperCarmack) (April 3, 2024). "When loading the save for comparison, you need to wait a little bit because the light glows are scripted to come on after a delay. So 1 = dx8, 2 = dx9 on load, 3 = dx9 after 5 seconds".  X (Twitter). Retrieved September 14, 2025..

See also

• Env volumetric fog volume
• Env volumetric fog controller
• Working With Volumetrics
• WiseVol

External links

• YOUTUBE How To Create Sunbeams using Volumetric Fog in Source 2 Hammer
• Volumetric fog imitation trick with env_projectedtexture and translucent models (showcase)
• Volumetric fog imitation trick with env_projectedtexture and translucent models (tutorial)
•  Volumetric fog