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

@@ -38,7 +38,6 @@ void MeshData::init()
     BKE_object_to_mesh_clear(object);
   }
 
-  write_material();
   write_transform();
 }
 
@@ -73,7 +72,7 @@ void MeshData::update()
   }
   else {
     if (id->recalc & ID_RECALC_SHADING) {
-      write_material();
+      write_material(nullptr);
       bits |= pxr::HdChangeTracker::DirtyMaterialId | pxr::HdChangeTracker::DirtyDoubleSided;
     }
     if (id->recalc & ID_RECALC_TRANSFORM) {
@@ -189,6 +188,7 @@ void MeshData::write_mesh(Mesh *mesh)
   vertices_.clear();
   normals_.clear();
   uvs_.clear();
+  face_material_indices_.clear();
 
   BKE_mesh_calc_normals_split(mesh);
   int tris_len = BKE_mesh_runtime_looptri_len(mesh);
@@ -219,9 +219,10 @@ void MeshData::write_mesh(Mesh *mesh)
 
   write_normals(mesh);
   write_uv_maps(mesh);
+  write_material(mesh);
 }
 
-void MeshData::write_material()
+void MeshData::write_material(Mesh *mesh)
 {
   Object *object = (Object *)id;
   Material *mat = nullptr;
@@ -233,6 +234,7 @@ void MeshData::write_material()
     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_) {
@@ -241,6 +243,18 @@ void MeshData::write_material()
     mat_data_->init();
     mat_data_->insert();
   }
+
+  if (mesh) {
+    face_material_indices_.clear();
+    const int *material_indices = BKE_mesh_material_indices(mesh);
+    const int *looptri_polys = BKE_mesh_runtime_looptri_polys_ensure(mesh);
+    int poly_ind;
+    blender::Span<MLoopTri> loopTris = mesh->looptris();
+    for (size_t i = 0; i < loopTris.size(); ++i) {
+      poly_ind = looptri_polys[i];
+      face_material_indices_.push_back(material_indices[poly_ind]);
+    }
+  }
 }
 
 void MeshData::write_uv_maps(Mesh *mesh)

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

@@ -14,6 +14,12 @@
 namespace blender::render::hydra {
 
 class MeshData : public ObjectData {
+  struct MaterialMesh {
+    pxr::VtIntArray face_vertex_counts;
+    pxr::VtIntArray face_vertex_indices;
+    MaterialData *mat_data = nullptr;
+  };
+
  public:
   MeshData(BlenderSceneDelegate *scene_delegate, Object *object, pxr::SdfPath const &prim_id);
 
@@ -35,7 +41,7 @@ class MeshData : public ObjectData {
 
  private:
   void write_mesh(Mesh *mesh);
-  void write_material();
+  void write_material(Mesh *mesh);
   void write_uv_maps(Mesh *mesh);
   void write_normals(Mesh *mesh);
 
@@ -45,6 +51,7 @@ class MeshData : public ObjectData {
   pxr::VtVec2fArray uvs_;
   pxr::VtVec3fArray normals_;
 
+  pxr::VtIntArray face_material_indices_;
   MaterialData *mat_data_ = nullptr;
 };