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

@@ -122,6 +122,18 @@ bool BlenderSceneDelegate::GetVisible(pxr::SdfPath const &id)
   return object_data(id)->visible;
 }
 
+bool BlenderSceneDelegate::GetDoubleSided(pxr::SdfPath const &id)
+{
+  CLOG_INFO(LOG_RENDER_HYDRA_SCENE, 3, "%s", id.GetText());
+  return mesh_data(id)->double_sided();
+}
+
+pxr::HdCullStyle BlenderSceneDelegate::GetCullStyle(pxr::SdfPath const &id)
+{
+  CLOG_INFO(LOG_RENDER_HYDRA_SCENE, 3, "%s", id.GetText());
+  return mesh_data(id)->cull_style;
+}
+
 pxr::SdfPath BlenderSceneDelegate::GetInstancerId(pxr::SdfPath const &prim_id)
 {
   CLOG_INFO(LOG_RENDER_HYDRA_SCENE, 3, "%s", prim_id.GetText());

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

@@ -21,8 +21,9 @@ namespace blender::render::hydra {
 extern struct CLG_LogRef *LOG_RENDER_HYDRA_SCENE; /* BSD - Blender Scene Delegate */
 
 class BlenderSceneDelegate : public pxr::HdSceneDelegate {
-  friend ObjectData; /* has access to instances */
-  friend MeshData;   /* has access to materials */
+  friend ObjectData;   /* has access to instances */
+  friend MeshData;     /* has access to materials */
+  friend MaterialData; /* has access to objects and instancers */
 
  public:
   enum class EngineType { VIEWPORT = 1, FINAL, PREVIEW };
@@ -43,6 +44,8 @@ class BlenderSceneDelegate : public pxr::HdSceneDelegate {
   pxr::SdfPath GetMaterialId(pxr::SdfPath const &rprim_id) override;
   pxr::VtValue GetMaterialResource(pxr::SdfPath const &material_id) override;
   bool GetVisible(pxr::SdfPath const &id) override;
+  bool GetDoubleSided(pxr::SdfPath const &id) override;
+  pxr::HdCullStyle GetCullStyle(pxr::SdfPath const &id) override;
   pxr::SdfPath GetInstancerId(pxr::SdfPath const &prim_id) override;
   pxr::SdfPathVector GetInstancerPrototypes(pxr::SdfPath const &instancer_id) override;
   pxr::VtIntArray GetInstanceIndices(pxr::SdfPath const &instancer_id,

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

@@ -228,6 +228,13 @@ void InstancerData::update_as_parent()
       prim_id, pxr::HdChangeTracker::AllDirty);
 }
 
+void InstancerData::update_double_sided(MaterialData *mat_data)
+{
+  for (auto &it : mesh_instances_) {
+    it.second.data->update_double_sided(mat_data);
+  }
+}
+
 pxr::SdfPath InstancerData::object_prim_id(Object *object) const
 {
   /* Making id of object in form like <prefix>_<pointer in 16 hex digits format> */

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

@@ -43,6 +43,7 @@ class InstancerData : public ObjectData {
   void check_remove(std::set<std::string> &available_objects);
   void available_materials(std::set<pxr::SdfPath> &paths) const;
   void update_as_parent();
+  void update_double_sided(MaterialData *mat_data);
 
  private:
   pxr::SdfPath object_prim_id(Object *object) const;

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

@@ -30,7 +30,7 @@ MaterialData::MaterialData(BlenderSceneDelegate *scene_delegate,
 void MaterialData::init()
 {
   ID_LOG(2, "");
-
+  double_sided = (((Material *)id)->blend_flag & MA_BL_CULL_BACKFACE) == 0;
   material_network_map_ = pxr::VtValue();
 
   /* Call of python function hydra.export_mtlx() */
@@ -120,9 +120,21 @@ void MaterialData::remove()
 void MaterialData::update()
 {
   ID_LOG(2, "");
+  bool prev_double_sided = double_sided;
   init();
   scene_delegate_->GetRenderIndex().GetChangeTracker().MarkSprimDirty(prim_id,
                                                                       pxr::HdMaterial::AllDirty);
+  if (prev_double_sided != double_sided) {
+    for (auto &it : scene_delegate_->objects_) {
+      MeshData *m_data = dynamic_cast<MeshData *>(it.second.get());
+      if (m_data) {
+        m_data->update_double_sided(this);
+      }
+    }
+    for (auto &it : scene_delegate_->instancers_) {
+      it.second->update_double_sided(this);
+    }
+  }
 }
 
 pxr::VtValue MaterialData::get_data(pxr::TfToken const &key) const

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

@@ -27,6 +27,8 @@ class MaterialData : public IdData {
   pxr::VtValue get_data(pxr::TfToken const &key) const override;
   pxr::VtValue get_material_resource() const;
 
+  bool double_sided = true;
+
  private:
   pxr::SdfAssetPath mtlx_path_;
   pxr::VtValue material_network_map_;

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

@@ -74,7 +74,7 @@ void MeshData::update()
   else {
     if (id->recalc & ID_RECALC_SHADING) {
       write_material();
-      bits |= pxr::HdChangeTracker::DirtyMaterialId;
+      bits |= pxr::HdChangeTracker::DirtyMaterialId | pxr::HdChangeTracker::DirtyDoubleSided;
     }
     if (id->recalc & ID_RECALC_TRANSFORM) {
       write_transform();
@@ -119,6 +119,7 @@ bool MeshData::update_visibility()
 {
   bool ret = ObjectData::update_visibility();
   if (ret) {
+    ID_LOG(2, "");
     scene_delegate_->GetRenderIndex().GetChangeTracker().MarkRprimDirty(
         prim_id, pxr::HdChangeTracker::DirtyVisibility);
   }
@@ -164,6 +165,23 @@ pxr::SdfPath MeshData::material_id() const
   return mat_data_->prim_id;
 }
 
+bool MeshData::double_sided() const
+{
+  if (mat_data_) {
+    return mat_data_->double_sided;
+  }
+  return true;
+}
+
+void MeshData::update_double_sided(MaterialData *mat_data)
+{
+  if (mat_data_ == mat_data) {
+    ID_LOG(2, "");
+    scene_delegate_->GetRenderIndex().GetChangeTracker().MarkRprimDirty(
+        prim_id, pxr::HdChangeTracker::DirtyDoubleSided);
+  }
+}
+
 void MeshData::write_mesh(Mesh *mesh)
 {
   face_vertex_counts_.clear();

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

@@ -28,6 +28,10 @@ class MeshData : public ObjectData {
   pxr::HdMeshTopology mesh_topology() const;
   pxr::HdPrimvarDescriptorVector primvar_descriptors(pxr::HdInterpolation interpolation) const;
   pxr::SdfPath material_id() const;
+  bool double_sided() const;
+  void update_double_sided(MaterialData *mat_data);
+
+  pxr::HdCullStyle cull_style = pxr::HdCullStyleBackUnlessDoubleSided;
 
  private:
   void write_mesh(Mesh *mesh);