source/blender/render/hydra/scene_delegate/blender_scene_delegate.cc

@@ -147,8 +147,8 @@ void BlenderSceneDelegate::update_collection(bool remove, bool visibility)
 
     /* remove unused materials */
     std::set<pxr::SdfPath> available_materials;
-    for (auto &obj : objects) {
+    for (auto &it : objects) {
-      MeshData *m_data = dynamic_cast<MeshData *>(obj.second.get());
+      MeshData *m_data = dynamic_cast<MeshData *>(it.second.get());
       if (!m_data) {
         continue;
       }
@@ -157,6 +157,9 @@ void BlenderSceneDelegate::update_collection(bool remove, bool visibility)
         available_materials.insert(mat_id);
       }
     }
+    for (auto &it : instancers) {
+      it.second->available_materials(available_materials);
+    }
     for (auto it = materials.begin(); it != materials.end(); ++it) {
       if (available_materials.find(it->first) != available_materials.end()) {
         continue;

source/blender/render/hydra/scene_delegate/instancer.cc

@@ -152,6 +152,16 @@ void InstancerData::check_remove(pxr::SdfPath const &obj_id)
       p_id, pxr::HdChangeTracker::AllDirty);
 }
 
+void InstancerData::available_materials(std::set<pxr::SdfPath> &paths)
+{
+  for (auto &it : instances) {
+    pxr::SdfPath mat_id = ((MeshData *)it.second.obj_data.get())->material_id();
+    if (!mat_id.IsEmpty()) {
+      paths.insert(mat_id);
+    }
+  }
+}
+
 void InstancerData::set_instances()
 {
   transforms.clear();

source/blender/render/hydra/scene_delegate/instancer.h

@@ -37,6 +37,7 @@ class InstancerData : public ObjectData {
   pxr::SdfPathVector prototypes();
   void check_update(Object *object);
   void check_remove(pxr::SdfPath const &obj_id);
+  void available_materials(std::set<pxr::SdfPath> &paths);
 
  private:
   void set_instances();