Yes. The idea here is that ambient lights pass through objects so if there are parallel surfaces where reflected lighting or shadows will
traverse a large area you can apply this same lighting behavior to a large swath of geometry. You just have to divide your space into
Prior to this, traditional Quake mappers thought that using lots of custom textures for lights would waste texture re-use but Lunaran found
that the engine doesn't really re-use textures on lights anyway. Eg. you might as well use the feature if you are going to waste the resources
on it either way.
Edit: Here are the words of the author:
Wow.. Okay, tutorials/strategies for painting light textures for ambient lights, please. That whole idea is dead secksy.
Well, this one isn't for an ambient light but the principle is the same. You've got a light source in a room, and that light is going to spread out from the source in volumes. The trick is visualizing what direction you can project a 2d image from that will let you most closely map those volumes.
Take the first side room. With the main light source (the skylight) directly above, it'd be impossible to project an image from above that fits the way the light spreads out as it comes down. But from the side:
all the angles of the shape of the room and the shadows they cast can be seen at once. Thus, we take the room from the side:
and through the magic of photoshop we make a light image that looks like this (minus the white outlines, those are just for visualization):
This is mostly radial/linear gradients and some masking. The dark bit in the lower right corresponds to the machines running the length of the room, and contributes some softened darkness to the corners where you can see behind/inside them. Make a light shader out of it, and rotate the light volume in the editor so that the top is turned to the side, and the projection happens from the direction we want. You can see the softness of the shadow against the far wall in the first image now.
You can now make a second z-image with dark stripes for the columns or a big dark splotch for that bridge in the distance, because those features fit the second axis of the volume the best. Fog brush on the ceiling to mimic some volumetric glare, give the ambient light in this room a similar (but much more blurry) treatment to fill the black shadows in, and you're sold.
That's probably not the best explanation since it's 4am and I'm rushing, but I think it helps visualize the idea. Rooms with more funky shapes can be achieved with multiple volumes fitted to the room shape, and you can paint dark areas that line up between two images so that when the lights overlap they add over each other to hide the seam.
I actually had to do this for the room in the example, since at the far end that bridge divides the room vertically, so I need a second light volume there with the same image cropped to the top half, so the volume doesn't need to extend below the bridge (which would be pointless overdraw as it's supposed to be dark down there. There's also a bounce light above the bridge shining back up at the ceiling, because having a big white concrete floor right there so close to the skylight would be reflecting a bunch more light straight back up.
So, yeah. Lighting!