Missing triangles/holes in surface mesh (fixed, update to 1.0.4a)

[niklassjogren]

System Information

Blender Version (including hash):
Blender 2.79b Hash:f4dc9f9d68b
FLIP Fluids Version:
1.0.4
Operating System:
Windows 10
CPU:
Intel i7-6850K @ 3.60GHx
GFX:
Nvidia GTX 1070
Nvidia GTX 970
Driver 398.36
RAM:
32GB

Describe the bug

I do see a lot of holes, missing polygons (non-manifold geometry) that I didn't notice in earlier versions?

To Reproduce

Imported geometry (Alembic), made a domain and fluid in Blender, tried the Coffee preset for settings!

Expected Behaviour

No missing polygons!

Actual Behaviour

some missing polygons in the fluid mesh, see screenshots!

Screenshots

If applicable, add screenshots to help explain your problem.

After a Shift-Ctrl-Alt-M (non-manifold geometry):

[rlguy]

Hey niklassjogren,

Thanks for letting me know abut this! This could be an issue new particle mesher in 1.0.4. Would you be able to attach a .blend file that reproduces this issue?

- Ryan

[niklassjogren]

Yes of course! I uploaded them and shared them from my dropbox, the .zip also includes all the files including the Cache if needed! I hope that works?
https://www.dropbox.com/sh/e4fkakhc1tzdexw/AABaHc76Ntpe653OEwdsDdZNa?dl=0

/niklas

[rlguy]

Hello niklas,

Just giving an update on this issue. The problem that is causing the holes in the fluid mesh has been found and a solution for how to fix this is understood. However, while investigating this issue we have identified some other problems within the new particle mesher that are also causing chunks of the mesh to be incomplete.

Non-manifold parts within the fluid mesh is quite a serious issue as this has consequences in rendering. Our priority at the moment is fixing all issues within the particle mesher. We will be releasing a patched version (1.0.4a) as soon as we can fix these problems and test the updates. Hopefully within one week.

The issues are related to the domain size (and world scaling) and also number of mesh subdivisions. Using small domains or small world scales in combination with higher mesh subdivisions (1 and 2) may increase the frequency of missing polygons. A workaround that may help is using domain sizes/scales larger than 5 metres wide and limiting number of subdivisions to a maximum of 1.

If a reliable mesher is needed, I would have to suggest reverting back to version 1.0.3 until these issues are fixed. Sorry for the inconvenience and thank you for your patience!

- Ryan

[rlguy]

This issue has been fixed and will be included in a patched version v1.0.4a that will be available August 24th, 2018. It is highly advised to upgrade to the patched version as this update will fix some major bugs within the particle mesher (#376, #377).

This bug was caused by numerical precision errors. The mesher calculates the surface mesh in chunks and then 'welds' the pieces together to join the vertices/edges. When triangles become small, there can be numerical errors in CPU calculations due to the finite amount of precision that a 32-bit number stores. These precision errors caused vertices not to line up properly and they would not become 'welded' together resulting in holes within the surface mesh. This issue has been fixed by internally scaling the mesh to an appropriate size so that the CPU can handle calculations accurately while joining mesh chunks.

[niklassjogren]

Sounds great, awesome work!