[BUG] Stacked sector portal + sky plane regression

[TehRealSalt]

GZDoom version

2c4ac88

Which game are you running with GZDoom?

None

What Operating System are you using?

Windows 10

Please describe your specific OS version

Windows 10 Pro

Relevant hardware info

CPU: 13th Gen Intel Core i3-13100F, 3.40 GHz; GPU: NVIDIA GeForce GTX 1060 6GB

Have you checked that no other similar issue already exists?

• I have searched and not found similar issues.

A clear and concise description of what the bug is.

Stacked sector portals are occasionally displaying erroneous sky planes, when connected to an area with sky planes. Where these planes appear depends on viewpoint and the geometry itself. Doing a git bisect shows that the issue starts appearing in 2c4ac88, and is not present in commits before.

Steps to reproduce the behaviour.

I've ported a piece of offending map geometry that was easy to isolate into a test WAD for Doom 2. Add this file ("portal-stack-test-2.wad") with Doom 2 as the IWAD, and open MAP01 to see the issue: portal-stack-test-2.zip

I haven't been able to find a conclusive pattern for which stacked portals do this and which don't quite yet. I made a minimal example stacked portal w/ a sky plane nearby to test this issue, and saw no rendering issues with it.

Your configuration

No response

Provide a Log

No response

[dileepvr]

Thanks for catching that!
Hopefully this fixes it in your full map as well.

[TehRealSalt]

Thanks for catching that! Hopefully this fixes it in your full map as well.

I'm a bit late since it's already merged, but it indeed fixes my issue! Thank you!

[TehRealSalt]

Sorry, I might've been a bit quick on the draw. All of my other sector portal usage is working again (including the original test case) after 0b30b4a, except for this one particular complex stacked setup that I have, which involves several stacked sector portals in the same area.

When viewed from above, this portal is randomly either a sky plane or pitch black. What's interesting is that it is always working when viewed from below. This behavior is identical between 2c4ac88 and 0b30b4a.

---

Behavior on dc5a250

Floor portal

Expected behavior

Ceiling portal

Expected behavior

---

Behavior on both 2c4ac88 and 0b30b4a

Floor portal

Depending on viewpoint, is either sky plane or pitch black.

Ceiling portal

Expected behavior

---

These portals encompass a lot of the map, so it's harder to isolate a test case; I've uploaded the entire map directly w/ the bare minimal alterations to work in Doom 2. You can view one of the offending portals by loading MAP01, using fly / noclip2, moving directly upwards, and then looking down: portal-stack-test-3.zip

Thank you for looking into this so far, though!

[TehRealSalt]

Testing 60ebd71, it's getting closer to perfect! However, in the room directly to the north of the start, a seemingly arbitrary upper slice of the geometry vanishes when viewed through the floor portal, and only from certain locations:

As taken from the Doom-ported geometry:

It might be worth noting that this still only happening when looking down through a floor portal. I have not witnessed any issues looking up through a ceiling portal.

[dileepvr]

;__;
Hopefully a new one-line PR will resolve this. Terribly sorry to put you through this.
My testing wasn't exhaustive enough. I had no idea stacked sectors could be used this way.

Is your project public? It looks very interesting.

[TehRealSalt]

I ran a search over all of my maps & WIPs for any uses of stacked portals I might've forgotten, and I did not see any remaining issues under 74594e4. I think everything is truly fixed now, thank you!!

Terribly sorry to put you through this. My testing wasn't exhaustive enough. I had no idea stacked sectors could be used this way.

It was not a problem for me at all; I would imagine portal rendering is finicky, and it's the least I can do to help prevent future bug reports for a later GZDoom release. I only happened to catch the issue when I wanted to try out the netcode changes. Thank you for being prompt with it!

I tend to use sector portals a lot as pseudo-layers. Makes overlapping geometry much nicer, especially compared to the alternative of spamming 3D floors.

Is your project public? It looks very interesting.

It's called Snap the Sentinel -- there's two public versions out right now:

• Older, but full 10-map single episode on itch.io: https://tehrealsalt.itch.io/snap-the-sentinel
• More polished, but shorter 5-map demo on Steam: https://store.steampowered.com/app/1739960/Snap_the_Sentinel/

These are both free; some of the stuff I've been uploading for this bug report are for a 20-map version that isn't out yet, and my current plan is to eventually sell that version.