Mapblock occlusion culling can hide visible geometry

[paulevsGitch]

Minetest version

Minetest 5.8.0 (release)

Irrlicht device

No response

Operating system and version

Windows 10, 64 bit

CPU model

Intel Core i9-10900F

GPU model

NVIDIA GeForce RTX 3060

Active renderer

OpenGL 4.6.0

Summary

In some cases occlusion culling can be too aggressive and cull visible geometry. That happens when another mapblock slightly overlaps hidden geometry, example (sand near cliffs):

Same place with different angle - geometry is not occluded:

That happens with both "loops" and "bfs", independently from enabled/disabled "raytraced occlusion" and "server occlusion culling"

Steps to reproduce

This bug can be reproduced in different games, for example in this one, or you can see similar bug in backrooms test

[sfan5]

The occlusion culler is indeed quite approximate and not very good, so this is "just" a symptom of that.

[paulevsGitch]

There are several articles and sources that can potentially help to improve occluder:

• The Advanced Cave Culling Algorithm by Tommo: https://tomcc.github.io/index.html
• C# implementation used in Vintage Story game: https://github.com/tyronx/occlusionculling