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

@@ -126,6 +126,10 @@ pxr::SdfPath BlenderSceneDelegate::GetMaterialId(pxr::SdfPath const &rprim_id)
   if (c_data) {
     return c_data->material_id();
   }
+  VolumeData *v_data = volume_data(rprim_id);
+  if (v_data) {
+    return v_data->material_id();
+  }
   return pxr::SdfPath();
 }
 
@@ -600,6 +604,10 @@ void BlenderSceneDelegate::remove_unused_objects()
     if (c_data) {
       c_data->available_materials(available_materials);
     }
+    VolumeData *v_data = dynamic_cast<VolumeData *>(val.get());
+    if (v_data) {
+      v_data->available_materials(available_materials);
+    }
   }
   for (auto &val : instancers_.values()) {
     val->available_materials(available_materials);

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

@@ -29,6 +29,7 @@ class Engine;
 class BlenderSceneDelegate : public pxr::HdSceneDelegate {
   friend ObjectData;   /* has access to instances */
   friend CurvesData;   /* has access to materials */
+  friend VolumeData;   /* has access to materials */
   friend MeshData;     /* has access to materials */
   friend MaterialData; /* has access to objects and instancers */
 

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

@@ -9,6 +9,7 @@
 #include <pxr/usdImaging/usdVolImaging/tokens.h>
 
 #include "BKE_volume.h"
+#include "BKE_material.h"
 #include "DNA_volume_types.h"
 #include "BLI_index_range.hh"
 
@@ -34,6 +35,7 @@ void VolumeData::init()
   }
   filepath_ = BKE_volume_grids_frame_filepath(volume);
   write_transform();
+  write_materials();
   BKE_volume_unload(volume);
 }
 
@@ -66,6 +68,27 @@ void VolumeData::remove()
 
 void VolumeData::update()
 {
+  Object *object = (Object *)id;
+  pxr::HdDirtyBits bits = pxr::HdChangeTracker::Clean;
+  if ((id->recalc & ID_RECALC_GEOMETRY) || (((ID *)object->data)->recalc & ID_RECALC_GEOMETRY)) {
+    init();
+    bits = pxr::HdChangeTracker::AllDirty;
+  }
+  if (id->recalc & ID_RECALC_SHADING) {
+    write_materials();
+    bits |= pxr::HdChangeTracker::DirtyMaterialId | pxr::HdChangeTracker::DirtyDoubleSided;
+  }
+  if (id->recalc & ID_RECALC_TRANSFORM) {
+    write_transform();
+    bits |= pxr::HdChangeTracker::DirtyTransform;
+  }
+
+  if (bits == pxr::HdChangeTracker::Clean) {
+    return;
+  }
+
+  scene_delegate_->GetRenderIndex().GetChangeTracker().MarkRprimDirty(prim_id, bits);
+  ID_LOG(1, "");
 }
 
 pxr::VtValue VolumeData::get_data(pxr::SdfPath const &id, pxr::TfToken const &key) const
@@ -131,4 +154,43 @@ pxr::HdVolumeFieldDescriptorVector VolumeData::volume_field_descriptors() const
   return volume_field_descriptors;
 }
 
+pxr::SdfPath VolumeData::material_id() const
+{
+  if (!mat_data_) {
+    return pxr::SdfPath();
+  }
+  return mat_data_->prim_id;
+}
+
+void VolumeData::available_materials(Set<pxr::SdfPath> &paths) const
+{
+  if (mat_data_ && !mat_data_->prim_id.IsEmpty()) {
+    paths.add(mat_data_->prim_id);
+  }
+}
+
+void VolumeData::write_materials()
+{
+  Object *object = (Object *)id;
+  Material *mat = nullptr;
+  /* TODO: Using only first material. Add support for multimaterial. */
+  if (BKE_object_material_count_eval(object) > 0) {
+    mat = BKE_object_material_get_eval(object, 0);
+  }
+
+  if (!mat) {
+    mat_data_ = nullptr;
+    return;
+  }
+  pxr::SdfPath p_id = scene_delegate_->material_prim_id(mat);
+  mat_data_ = scene_delegate_->material_data(p_id);
+  if (!mat_data_) {
+    scene_delegate_->materials_.add_new(
+        p_id, std::make_unique<MaterialData>(scene_delegate_, mat, p_id));
+    mat_data_ = scene_delegate_->material_data(p_id);
+    mat_data_->init();
+    mat_data_->insert();
+  }
+}
+
 }  // namespace blender::render::hydra

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

@@ -23,9 +23,14 @@ class VolumeData : public ObjectData {
   bool update_visibility() override;
 
   pxr::HdVolumeFieldDescriptorVector volume_field_descriptors() const;
+  pxr::SdfPath material_id() const;
+  void available_materials(Set<pxr::SdfPath> &paths) const;
 
  private:
+   void write_materials();
+
    std::string filepath_;
+   MaterialData *mat_data_ = nullptr;
 };
 
 }  // namespace blender::render::hydra