[BUG] Lightmode 5 ("Build") is buggy in GZDoom

[TheKins]

GZDoom version

GZDoom g4.15pre-73-ge1297803

Which game are you running with GZDoom?

Doom 2

What Operating System are you using?

Windows 10

Please describe your specific OS version

No response

Relevant hardware info

Nvidia GTX 1070 GPU, observed on other hardware

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.

When defined in MAPINFO, Lightmode 5 (the "Build Engine" lightmode imported from Raze) is oddly buggy, with sprites and surfaces inexplicably turning pitch black from certain angles in ways that are not present in other light modes.

Example, using an unreleased port of a map from LameDuke to GZDoom:

• With Default Lightmode
• With Lightmap 5

Steps to reproduce the behaviour.

Explain how to reproduce

1. Add "lightmode = 5" to the MAPINFO definition of a reasonably modern GZDoom map

Your configuration

Witnessed on multiple systems with differing INI files.

Provide a Log

No response

[TheKins]

From a friend working on another (non-public) map that hit the same issue:

Again, if it's worth noting, I started running into it when adding 3D floors with different lighting levels than the sector they were assigned to. I don't know if you used 3D floors for your map too
But that might help them pinpoint the issue, if you can add that
My map was rendering fine in this mode until I added a single 3D floor with a lighting difference, and that's when everything went to hell

[RicardoLuis0]

IIRC it's been broken and unsupported for a long while, don't know if graf will ever fix it

[TheKins]

A pity, but kind of understandable seeing as it's a really obscure, obscured-from-users feature that's only really there as a hangover from Raze development. Hopefully it gets jiggled into compliance at some point, but like, I understand.