Can we fix 4D maps ?

by **SeaWyrm** » Wed Jun 03, 2015 10:37 pm

4D maps open up all sorts of interesting design possibilities, and me, I'm keen on exploring them.
Thing is, there's that texture glitching problem. Which sucks.
Does anybody know what it would take to fix that? Could it be handled in a mod/patch or something? Or is there an existing workaround to make it stop happening? I think someone told me at some point it's a Rebirth problem, not a Descent problem - is that correct?
I don't have much free time these days, but I'm nevertheless very willing to put in the effort to fix this issue, if it is indeed fixable.

by **Sirius** » Wed Jun 03, 2015 10:57 pm

I presume the issue is the way original Descent handled drawing order, versus how OpenGL does it. Descent walked through the mine from the player's location to construct a tree of visible cubes and then drew them from the deepest level upward. OpenGL, well... it basically just uses a depth-buffer to do that on a per-pixel basis. So it'll just draw the nearest face, and if they're co-planar, you'll see z-fighting.

I figure it would be possible to re-implement the OpenGL renderer so that it emulates the original game's software renderer, but not having actually studied it I couldn't tell you how much work it'd be. You'd also reintroduce the weaknesses in the original renderer; it occasionally drew faces in the wrong order even when 4D wasn't the intention.

by **Drakona** » Thu Jun 04, 2015 9:58 am

Halls of Iconia still looks pretty stable, and it always has. Might be worth studying to see why.

by **Entropy** » Thu Jun 04, 2015 3:57 pm

Morfod and I just played a game on Halls of Iconia and it has aroudn 4-6 instances of the graphics issue with 4D levels. Some were pretty rare but the one on the blue door happened almost all the time. I think fixing this would be really worthwhile, but I am sort of aware of how much effort this might take.

by **Drakona** » Thu Jun 04, 2015 5:32 pm

Oh, I see! Yeah, it didn't used to do that in the D1x era, I don't think. I don't know if it's a GL issue, exactly, or if something changed. I remember iconia being stable, and I played it a lot, and I think I was on the GL version of D1x in that era. I could be wrong, though. It was all so long ago, and memory fades.

Would be worth checking into, and it's nice that that one case is so easy to reproduce.

by **SeaWyrm** » Thu Jun 04, 2015 7:30 pm

I'm not remotely the computer graphics expert that I'd like to be someday, but I know at least a thing or two about OpenGL... if someone points me in the direction of some source code, I can start digging and see what I turn up?

by **melvin** » Thu Jun 04, 2015 8:18 pm

I dont remember it doing that and it was my home level, FWIW.

by **Drakona** » Thu Jun 04, 2015 9:16 pm

It was my home level on IDL, too. It didn't do that.

by **Drakona** » Thu Jun 04, 2015 9:19 pm

Seawyrm, the code lives at: https://github.com/CDarrow/DXX-Retro

by **Sirius** » Thu Jun 04, 2015 10:12 pm

I recall back when I was building level 7 of Obsidian, I had a couple areas which accidentally overlapped, and robots could see you from the other overlapping area, and their homing missiles would actually track and damage you - you just couldn't see or hear any of it.

Did "4D" levels have the same phenomenon in multiplayer? I think I talked to MD-1224 about this once but I forget what he said...