Fix: USD: Prevent unsupported point instancing setups from causing warns

If we detect an unsupported point instancing setup, do not attempt to
still export it out. Depending on the number of instances this can spew
10's of thousands of USD warning traces to the console.

Pull Request: https://projects.blender.org/blender/blender/pulls/147253

source/blender/io/common/intern/abstract_hierarchy_iterator.cc

@@ -667,7 +667,7 @@ void AbstractHierarchyIterator::make_writers(const HierarchyContext *parent_cont
     if (!transform_writer) {
       /* Unable to export, so there is nothing to attach any children to; just abort this entire
        * branch of the export hierarchy. */
-      return;
+      continue;
     }
 
     const bool need_writers = context->is_point_proto || (!context->is_point_instance &&

source/blender/io/usd/intern/usd_hierarchy_iterator.cc

@@ -149,23 +149,22 @@ USDExporterContext USDHierarchyIterator::create_usd_export_context(const Hierarc
   return exporter_context;
 }
 
-void USDHierarchyIterator::determine_point_instancers(const HierarchyContext *context)
+bool USDHierarchyIterator::determine_point_instancers(const HierarchyContext *context)
 {
   if (!context) {
-    return;
+    return true;
   }
 
   if (context->object->type == OB_ARMATURE) {
-    return;
+    return true;
   }
 
+  bool is_referencing_self = false;
   if (context->is_point_instancer()) {
     /* Mark the point instancer's children as a point instance. */
     USDExporterContext usd_export_context = create_usd_export_context(context);
     const ExportChildren *children = graph_children(context);
 
-    bool is_referencing_self = false;
-
     pxr::SdfPath instancer_path;
     if (!params_.root_prim_path.empty()) {
       instancer_path = pxr::SdfPath(params_.root_prim_path + context->export_path);
@@ -243,6 +242,8 @@ void USDHierarchyIterator::determine_point_instancers(const HierarchyContext *co
       }
     }
   }
+
+  return !is_referencing_self;
 }
 
 AbstractHierarchyWriter *USDHierarchyIterator::create_transform_writer(
@@ -251,7 +252,12 @@ AbstractHierarchyWriter *USDHierarchyIterator::create_transform_writer(
   /* The transform writer is always called before data writers,
    * so determine if the #Xform's children is a point instancer before writing data. */
   if (params_.use_instancing) {
-    determine_point_instancers(context);
+    if (!determine_point_instancers(context)) {
+      /* If we could not determine that our point instancing setup is safe, we should not continue
+       * writing. Continuing would result in enormous amounts of USD warnings about cyclic
+       * references. */
+      return nullptr;
+    }
   }
 
   return new USDTransformWriter(create_usd_export_context(context));

source/blender/io/usd/intern/usd_hierarchy_iterator.hh

@@ -51,7 +51,7 @@ class USDHierarchyIterator : public AbstractHierarchyIterator {
 
  protected:
   bool mark_as_weak_export(const Object *object) const override;
-  void determine_point_instancers(const HierarchyContext *context);
+  bool determine_point_instancers(const HierarchyContext *context);
 
   AbstractHierarchyWriter *create_transform_writer(const HierarchyContext *context) override;
   AbstractHierarchyWriter *create_data_writer(const HierarchyContext *context) override;