Camera exposure pass

[dpJudas]

Pull request: https://github.com/coelckers/gzdoom/pull/105

Adds an additional pass that calculates the average brightness of a rendered scene and uses that to find the final camera exposure value. This improves the bloom pass in situations such as winter maps where the scene is very bright, and in scenes where it is very dark. The old exposure value was calculated by looking at the sector light value, but this did not provide a good basis for exposure calculations.

Probably better not to apply until after the release. It works fine on my computer, but one never knows..

[Major Cooke]

Actually, that is a very annoying issue especially on DRMS which had small strips of lights surrounded by a ton of dark flats. This could be extremely useful.

[dpJudas]

Those small strips will get more bloomy with this patch. Not sure if that's what you're hoping for.

[Major Cooke]

Well, whenever standing over those strips of light, FWOOOSH. The whole scene starts changing. The fact it kept escalating up and down a lot is the problem I had.

[dpJudas]

Oh, yeah, that was the old exposure code seeing you standing in a bright sector and turning down the exposure. It doesn't do that anymore. Now you have to look straight into a strip and have it cover most of the screen for something like that to happen.

[Graf Zahl]

I'm going to have to trust you here. Can you point me to something where this makes a difference?

[dpJudas]

There are a couple of places where you can really spot the difference:

Winter maps like WolfenDoom: Blade of Agony's map c2m6_a. Before this patch the bloom would blur the white sky reducing a lot how far you could see. This was the main motivation for adding this.

In Doom e1m5 at the very end there's a extremely dark room where the light pulsates up and down. If you don't grab the light googles and instead fire off your gun you'll see it bloom far more, along with the exploding barrels and shooting enemies. This happens because the eye doesn't manage to get used to the short moments of light. The player is overwhelmed by the light bursts so to speak. There are a few other places like the maze area of e1m2 and some Doom 2 maps that have similar effects.

Overall the goal was to make no real big changes in the typical Doom maps while fixing really bright stuff like BoA's winter maps.