Depsgraph: Driver Relations, skip finding possible relation with one driver

The `build_driver_relations()` function in the depsgraph relations builder
adds relations between drivers that potentially write to the same memory
location. This of course is only useful when there are two or more drivers.

1 files changed, 4 insertions, 0 deletions

diff --git a/source/blender/depsgraph/intern/builder/deg_builder_relations.cc b/source/blender/depsgraph/intern/builder/deg_builder_relations.cc
index 17de0e0b016..40fbfbc2b99 100644
--- a/source/blender/depsgraph/intern/builder/deg_builder_relations.cc
+++ b/source/blender/depsgraph/intern/builder/deg_builder_relations.cc
@@ -2806,6 +2806,10 @@ void DepsgraphRelationBuilder::build_driver_relations(IDNode *id_node)
     // For each node in the driver group, try to connect it to another node
     // in the same group without creating any cycles.
     int num_drivers = prefix_group.second.size();
+    if (num_drivers < 2) {
+      // A relation requires two drivers.
+      continue;
+    }
     for (int from_index = 0; from_index < num_drivers; ++from_index) {
       Node *op_from = prefix_group.second[from_index];