I have had a few requests for more information on how I did the volumetric lighting in my factory scene, so I’ll post the response I gave here. I may go a bit further in depth later on, but this should help you get what you need.
The volume lighting was done by making a grid of faces as in the example picture below. Each face was mapped with a texture that was a solid yellow, and had an alpha channel that faded off to the edges of the face. The material for that was an unlitGeneric, with these flags:
The window itself was a regular model. On the alpha channel is black, with a bit of lighter parts where I wanted it to light up and glow a bit. The material was a vertexLitGeneric, with this flag:
Be aware that I have had some issues with this though. One major problem was that occasionally some models sitting inside of the volume would not have the additive effect applied to them, appearing darker than the surrounding BSP geometry. This seemed to come and go however, and luckily on my final version of the map it wasn’t causing any troubles. I was also using HDR for this, I’m not sure how good it would look without it.