Node boxes with ±0.5 size z-fight with liquid

[ryvnf]

Luanti version

Luanti 5.11.0-dev-29cfb6eff (Linux)
Using LuaJIT 2.1.0-beta3
Built by GCC 12.2
Running on Linux/6.1.0 x86_64
BUILD_TYPE=Release
RUN_IN_PLACE=0
USE_CURL=1
USE_GETTEXT=1
USE_SOUND=1
STATIC_SHAREDIR="/usr/local/share/luanti"

Operating system and version

Debian GNU/Linux 12 (bookworm)

CPU model

No response

GPU model

No response

Active renderer

No response

Summary

A similar problem has been reported for "allfaces" previously #9324. #13569 suggests that this was fixed in 5.7.0, then broken in 5.8.0-dev and fixed again. #9324 should probably be closed. The problem does however also exist with nodeboxes which this issue is about.

Since it is so common for nodeboxes to specify ±0.5 as their size, this affects pretty much all games. So I think it should be fixed in the engine.

I think one possible solution is to offset the liquid face by the polygon offset depth bias as mentioned in #15634 so it is not drawn directly on top of a nodebox of 1 unit width. Alternatively the size of nodeboxes with borders at ±0.5 could automatically be made larger by the polygon offset depth bias but that is more likely to cause problems with mods that uses overlays on top of nodeboxes (like decorated pots in Mineclonia).

Steps to reproduce

Start the Development Test game and place some of the nodebox test nodes underwater. See attached screenshot.

It looks worse for nodes which have higher contrast to water, like many nodes in Mineclonia.

[sfan5]

Any chance you could bisect this?

[ryvnf]

I tried bisecting and found that the problem exists in 5.5.0. Unfortunately I get compilation errors which I struggle to resolve when going further back.

[sfan5]

Good enough. I was mainly worried that some recent change caused it.

[ryvnf]

I made a PR with a proposed fix #15783 just now. It culls the z-fighting faces like is done for leaves and glass.