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Null FtF pink thing on floor

PostPosted: Thu May 02, 2019 4:31 pm
by Enjay
Mod
viewtopic.php?f=19&t=59100

exe used
g4.2pre-17-gb23958b20

System
gtx-1080, Windows 10, current drivers

Picture


Image

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.

Re: Null FtF pink thing on floor

PostPosted: Sat May 04, 2019 2:53 pm
by Graf Zahl
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.

Re: Null FtF pink thing on floor

PostPosted: Sat May 04, 2019 3:23 pm
by Rachael
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.

Re: Null FtF pink thing on floor

PostPosted: Sat May 04, 2019 3:37 pm
by Graf Zahl
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.

Re: Null FtF pink thing on floor

PostPosted: Sat May 04, 2019 3:52 pm
by Rachael
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.

Re: Null FtF pink thing on floor

PostPosted: Sat May 04, 2019 4:23 pm
by Enjay
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.