Fix T84757: feedback loop with when modifying vertex group with nodes

The issue was that the mesh shared its vertex weights with the
original mesh (to reduce memory consumption). The solution is
to make a local copy of the vertex weights in this case.

1 files changed, 5 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/attribute_access.cc b/source/blender/blenkernel/intern/attribute_access.cc
index a7939beae90..2e1094364fd 100644
--- a/source/blender/blenkernel/intern/attribute_access.cc
+++ b/source/blender/blenkernel/intern/attribute_access.cc
@@ -1191,6 +1191,11 @@ WriteAttributePtr MeshComponent::attribute_try_get_for_write(const StringRef att
     if (mesh_->dvert == nullptr) {
       BKE_object_defgroup_data_create(&mesh_->id);
     }
+    else {
+      /* Copy the data layer if it is shared with some other mesh. */
+      mesh_->dvert = (MDeformVert *)CustomData_duplicate_referenced_layer(
+          &mesh_->vdata, CD_MDEFORMVERT, mesh_->totvert);
+    }
     return std::make_unique<blender::bke::VertexWeightWriteAttribute>(
         mesh_->dvert, mesh_->totvert, vertex_group_index);
   }