Geometry Nodes: Allow attribute nodes to use different domains

Currently every attribute node assumes that the attribute exists on the
"points" domain, so it generally isn't possible to work with attributes
on other domains like edges, polygons, and corners.

This commit adds a heuristic to each attribute node to determine the
correct domain for the result attribute. In general, it works like this:
 - If the output attribute already exists, use that domain.
 - Otherwise, use the highest priority domain of the input attributes.
 - If none of the inputs are attributes, use the default domain (points).

For the implementation I abstracted the check a bit, but in each
node has a slightly different situation, so we end up with slightly
different `get_result_domain` functions in each node. I think this makes
sense, it keeps the code flexible and more easily understandable.

Note that we might eventually want to expose a domain drop-down to some
of the nodes. But that will be a separate discussion; this commit focuses
on making a more useful choice automatically.

Differential Revision: https://developer.blender.org/D10389

1 files changed, 4 insertions, 0 deletions

diff --git a/source/blender/nodes/NOD_geometry_exec.hh b/source/blender/nodes/NOD_geometry_exec.hh
index 91d46e3951f..222aa559e8a 100644
--- a/source/blender/nodes/NOD_geometry_exec.hh
+++ b/source/blender/nodes/NOD_geometry_exec.hh
@@ -222,6 +222,10 @@ class GeoNodeExecParams {
                                                const GeometryComponent &component,
                                                const CustomDataType default_type) const;
 
+  AttributeDomain get_highest_priority_input_domain(Span<std::string> names,
+                                                    const GeometryComponent &component,
+                                                    const AttributeDomain default_domain) const;
+
  private:
   /* Utilities for detecting common errors at when using this class. */
   void check_extract_input(StringRef identifier, const CPPType *requested_type = nullptr) const;