Currently the realize instances code (which is also used by the join
geometry node) always creates generic attributes instead of vertex
groups. The expectation was that vertex groups would be replaced
by some form of generic attribute sooner rather than later. However,
it's clear that won't happen for some time, and this issue causes users
a lot of trouble. This commit preserves the vertex groups through the
operation. Any attribute name that was a vertex group on any of the
input meshes will become a vertex group in the result.
In the code this is a simple change because the attribute writer
abstraction allows writing to vertex groups as if the were just like
other contiguous arrays. In the future we could optimize the code
specifically for vertex groups.
This resolves the "bug" part of #99197 where the nodes remove vertex
groups. However, this doesn't change the fact that generating
primitive meshes in geometry nodes won't create vertex groups.
In general the property editor settings on the original mesh have
no effect on meshes created from scratch in geometry nodes.
Pull Request: https://projects.blender.org/blender/blender/pulls/131692
84c7684871