Discontinuity in geonode hair/fur when surface mesh is under deformation due to lack of tangent interpolation #128184

New Issue

Ducktor · 2024-09-26T15:00:42+02:00

Ducktor commented

2024-09-26 15:00:42 +02:00

System Information
Operating system: Windows 10
Graphics card: RTX 2080 Super Max-Q Design

Blender Version
Broken: 4.2 and all previous versions with geonode hair curves.
Worked: N/A

As described in node_geo_deform_curves_on_surface.cc in a comment at line 142, mesh tangents aren't interpolated across the surface when using surface deform for geonode, leading to discontinuity in the fur when the surface mesh is under deformation. This is usually seen as lines or breaks in the fur that seem to follow the topology of the mesh underneath.

This doesn't seem to be tracked anywhere (other than the comment), including the remaining hair curves issues TODO list in #125700

Exact steps for others to reproduce the error
Attached is a blend file showing a sphere with geonode hair and particle hair and a blend shape that deforms the sphere which shows, on the geonode hair sphere, a discontinuity in how the fur follows the mesh compared to the particle hair sphere. This probably isn't the perfect showcase of the issue, but I think it shows it well enough.

**System Information** Operating system: Windows 10 Graphics card: RTX 2080 Super Max-Q Design **Blender Version** Broken: 4.2 and all previous versions with geonode hair curves. Worked: N/A As described in [node_geo_deform_curves_on_surface.cc](https://projects.blender.org/blender/blender/src/commit/b8f236510d944eac395a2cac2ee2cd36f79b4aa9/source/blender/nodes/geometry/nodes/node_geo_deform_curves_on_surface.cc#L142) in a comment at line 142, mesh tangents aren't interpolated across the surface when using surface deform for geonode, leading to discontinuity in the fur when the surface mesh is under deformation. This is usually seen as lines or breaks in the fur that seem to follow the topology of the mesh underneath. This doesn't seem to be tracked anywhere (other than the comment), including the remaining hair curves issues TODO list in #125700 **Exact steps for others to reproduce the error** Attached is a blend file showing a sphere with geonode hair and particle hair and a blend shape that deforms the sphere which shows, on the geonode hair sphere, a discontinuity in how the fur follows the mesh compared to the particle hair sphere. This probably isn't the perfect showcase of the issue, but I think it shows it well enough.

tangents.blend

5.5 MiB

Ducktor added the

labels 2024-09-26 15:00:43 +02:00

~~Ducktor referenced this issue 2024-09-26 15:02:55 +02:00~~

Remaining issues with hair curves #125700

Ducktor referenced this issue

2024-09-26 15:03:31 +02:00

Remaining issues with hair curves #125700

Simon Thommes referenced this issue

2024-09-26 15:24:10 +02:00

Remaining issues with hair curves #125700

Simon Thommes commented

2024-09-26 15:26:06 +02:00

This is unfortunately probably another known issue at the moment, but it's good to track this with a specific use-case and attached blend file. I added it to the list in blender/blender#125700

Simon Thommes added

and removed

labels 2024-09-26 15:26:40 +02:00

Simon Thommes closed this issue