This patch implements basic support for evaluating function nodes on volume
grids. Conceptually, a function node always creates a new grid for the output,
though the output is often a modified version of the input. The topology of the
output grid is a union of all the input grids.
All input grids have to have the same transform. Otherwise one has to use
resampling to make grids compatible.
Non-grid inputs are allowed to be single values or fields. The fields are
evaluated in a voxel/tile context, so they compute a value per voxel or per
tile.
One optimization is missing that will probably be key in the future: the ability
to merge multiple function nodes and execute them at the same time. Currently
the entire function evaluation is started and finished for every function node
that outputs a grid. This will add significant overhead in some situations.
Implementing this optimization requires some more changes outside of the scope
of this patch though. It's good to have something that works first.
Note: Not all function nodes are supported yet, because we don't have grid types
for all of them yet. Most notably, there are no color/float4 grids yet.
Implementing those properly is not super straight forward and may require some
more changes, because there isn't a 1-to-1 mapping between grid types and socket
types (a float4 grid may correspond to a color or vector socket later on).
Using grids with function nodes and fields can result in false positive warnings
in the UI currently. That's a limitation of our current socket type inferencing
and can be improved once we have better socket shape inferencing.
Pull Request: https://projects.blender.org/blender/blender/pulls/125110
