This is essentially a left-over from the initial transition to fields where this was
forgotten. The mesh primitive nodes used to create a named uv map attribute
with a hard-coded name. The standard way to deal with that in geometry nodes
now is to output the attribute as a socket instead. The user can then decide
to store it as a named attribute or not.
The benefits of not always storing the named attribute in the node are:
* Improved performance and lower memory usage when the uv map is not
used.
* It's more obvious that there actually is a uv map.
* The hard-coded name was inconsistent.
The versioning code inserts a new Store Named Attribute node that
stores the uv map immediatly. In many cases, users can probably just
remove this node without affecting their final result, but we can't
detect that.
There is one behavior change which is that the stored uv map will be
a 3d vector instead of a 2d vector which is what the nodes originally created.
We could store the uv map as 2d vector inthe Store Named Attribute node,
but that has the problem that older Blender versions don't support this
and would crash immediately. Users can just change this to 2d vector
manually if they don't care about forward compatibility.
There is a plan to support 2d vectors more natively in geometry nodes: T92765.
This change breaks forward compatibility in the case when the uv map
was used.
Differential Revision: https://developer.blender.org/D16637
Jacques Lucke
f879c20f72