ZDoom

I think what's really wanted here is just an opposite version of glowing flats, I'm assuming subtractive glowing flats were asked for since GZDoom by default has subtractive dynamic lights. I'm not sure too many people would actually care about the specific blending algorithm used, just that it gives the result of making things darker instead of brighter.

Subtractive lighting in general is bad. Lighting simply does not work that way, and I can understand it for a better "darkness" and "mystery" effect, it doesn't actually fade like light is supposed to. Here is an image to demonstrate the effect:

At full brightness this is an image (circa 1895, Photoglob Zürich, public domain) of the Roman Colosseum:
[imgur]https://imgur.com/iwvC8Dj[/imgur]

Here is the same image with a proper fade (multiplicative) applied to it:
[spoiler][imgur]https://imgur.com/I24I4ka[/imgur][/spoiler]

And here it is with a subtractive filter:
[spoiler][imgur]https://imgur.com/p2IRXId[/imgur][/spoiler]

Which of these look better? Notice with the multiplicative you don't lose the details, just the brilliance. The subtractive one, however, looks like the amateur fading algorithms that used to be present back in the DOS days before people actually discovered how to do them more accurately.

I can understand the reasoning behind the request and agree with that, but the methodology to achieve it is what I do not like.

Not sure about that one

Subtractive glowing flats would be super helpful for all the reasons Jaxxoon R listed.

A black or dark glow color is just that, an extremely dim glow. It can't be used to darken. Doom 64 lighting can't be used because it spans the height of the sector (including 3D floors) and so in cases involving certain pit setups would look awful. Drawing a texture would be limited to the resolution of the texture and won't actually affect the brightness of objects and geometry entering it. Subtractive lights can't be attenuated.

Even making the sector itself dark and lighting it with dynamic lights/glows will mean unwanted effects (glow gradient from no apparent light source, sudden darkness on walls facing away from dynamic lights, and using a large number of dynamic lights to even perform this effect in the first place).

How is this be different from attenuated lighting, or just drawing a darker texture, or using a glow feature with black?

Later Edit: IDK what I was thinking when I said this. I think I just didn't have enough experience with glows yet. This is definitely a good idea.

This feature could be really usefull! :D
It's pretty hard to achieve with dynamic light when you have multiple angled walls.