ZDoom

Graf Zahl wrote:Remember the glitch in the skybox? This looks to be the same thing.

I had a feeling that it might be a similar kind of problem.

Ah. And yeah, I remember that whole little thing with the portals being skies in the software renderer. It was pretty obvious with some of the glitches I've seen.

This is a side effect of how the portal's stencil gets created. It draws the outer bounds of the portal until a certain height and then caps it off at that height with a single polygon. The bug occurs if there's two portals being capped off recursively. The depth buffer simply cannot handle this case in a non-destructive way and the entire portal code is so dependent on this method that I haven't found a foolproof workaround that can handle all cases. What makes this so difficult is that the software renderer originally treated the portal like a sky, with all rendering anomalies that implies - and as you might guess, these anomalies have been exploited to hell and back tenfold by user maps dating back to 2005.

Why does this appear? It appears whenever there is a portal anywhere, directly above or below a player. If you view a sector portal, or a mirror, the effect appears, and it's been there since GZDoom's earliest days. I had always figured with something that's this persistent that it was a non-fixable bug, but I am still a bit curious how it technically happens.

Remember the glitch in the skybox? This looks to be the same thing. I knew the solution wasn't foolproof but my guess is that this map triggers the one case that cannot be reliably handled by what I did.

Mod
viewtopic.php?f=19&t=59100

exe used
g4.2pre-17-gb23958b20

System
gtx-1080, Windows 10, current drivers

Picture




See that pinkish shape that looks a bit like a pair of underpants?

I *think* I am looking through a portal from this viewpoint. It's only visible when standing on the ledge in the above shot and looking down. The pink shape moves with the player.