Geometry Nodes: support reading from spans of WriteAttribute

Previously, the span returned by `WriteAttribute`s might not contain the
current value of the attribute for performance reasons. To avoid some
bugs, the span now always contains the old values (they might have to
be copied over from the internal storage, dependending on how the
attribute is stored).
The old behavior is still available with the `get_span_for_write_only`
method. The span that it returns might not contain the current
attribute values. Therefore, it should only be used when you want
to overwrite an attribute without looking at the old values.

1 files changed, 1 insertions, 1 deletions

diff --git a/source/blender/nodes/geometry/nodes/node_geo_join_geometry.cc b/source/blender/nodes/geometry/nodes/node_geo_join_geometry.cc
index 80ac45aed4e..75736ae714a 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_join_geometry.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_join_geometry.cc
@@ -182,7 +182,7 @@ static void join_attributes(Span<const GeometryComponent *> src_components,
         write_attribute->domain() != domain) {
       continue;
     }
-    fn::GMutableSpan dst_span = write_attribute->get_span();
+    fn::GMutableSpan dst_span = write_attribute->get_span_for_write_only();
     fill_new_attribute(src_components, attribute_name, data_type, domain, dst_span);
     write_attribute->apply_span();
   }