Alembic Procedural: only subdivide if subsurf modifier is present

As subdivision objects are first class citizens in Alembic, to
differentiate them with non-subdivided polygon meshes, the Alembic
Procedural automatically sets up subdivision properties on the generated
Cycles Mesh.

However, for real-time playback subdivision is far too slow, so this
modifies the detection of a MeshSeqCache modifier used to activate the
procedural to allow for a Subsurf modifier right after the cache one. If
present, the procedural will tag the object for subdivision, if absent, the
object will be treated as a regular mesh.

This is a temporary measure for until subdivision surface settings are part
of the Mesh datablock (see T68891).

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D11162

intern/cycles/blender/blender_mesh.cpp

@@ -1078,7 +1078,7 @@ static void sync_mesh_cached_velocities(BL::Object &b_ob, Scene *scene, Mesh *me
     return;
   }
 
-  BL::MeshSequenceCacheModifier b_mesh_cache = object_mesh_cache_find(b_ob, true);
+  BL::MeshSequenceCacheModifier b_mesh_cache = object_mesh_cache_find(b_ob, true, nullptr);
 
   if (!b_mesh_cache) {
     return;
@@ -1241,7 +1241,7 @@ void BlenderSync::sync_mesh_motion(BL::Depsgraph b_depsgraph,
   }
 
   /* Cached motion blur already exported. */
-  BL::MeshSequenceCacheModifier mesh_cache = object_mesh_cache_find(b_ob, true);
+  BL::MeshSequenceCacheModifier mesh_cache = object_mesh_cache_find(b_ob, true, nullptr);
   if (mesh_cache) {
     return;
   }

intern/cycles/blender/blender_object.cpp

@@ -485,7 +485,9 @@ bool BlenderSync::sync_object_attributes(BL::DepsgraphObjectInstance &b_instance
 
 /* Object Loop */
 
-void BlenderSync::sync_procedural(BL::Object &b_ob, BL::MeshSequenceCacheModifier &b_mesh_cache)
+void BlenderSync::sync_procedural(BL::Object &b_ob,
+                                  BL::MeshSequenceCacheModifier &b_mesh_cache,
+                                  bool has_subdivision_modifier)
 {
 #ifdef WITH_ALEMBIC
   BL::CacheFile cache_file = b_mesh_cache.cache_file();
@@ -534,6 +536,8 @@ void BlenderSync::sync_procedural(BL::Object &b_ob, BL::MeshSequenceCacheModifie
   abc_object->set_subd_dicing_rate(subd_dicing_rate);
   abc_object->set_subd_max_level(max_subdivisions);
 
+  abc_object->set_ignore_subdivision(!has_subdivision_modifier);
+
   if (abc_object->is_modified() || procedural->is_modified()) {
     procedural->tag_update(scene);
   }
@@ -601,13 +605,14 @@ void BlenderSync::sync_objects(BL::Depsgraph &b_depsgraph,
     if (b_instance.show_self()) {
 #ifdef WITH_ALEMBIC
       bool use_procedural = false;
+      bool has_subdivision_modifier = false;
       BL::MeshSequenceCacheModifier b_mesh_cache(PointerRNA_NULL);
 
       /* Experimental as Blender does not have good support for procedurals at the moment, also
        * only available in preview renders since currently do not have a good cache policy, the
        * data being loaded at once for all the frames. */
       if (experimental && b_v3d) {
-        b_mesh_cache = object_mesh_cache_find(b_ob, false);
+        b_mesh_cache = object_mesh_cache_find(b_ob, false, &has_subdivision_modifier);
         use_procedural = b_mesh_cache && b_mesh_cache.cache_file().use_render_procedural();
       }
 
@@ -615,7 +620,7 @@ void BlenderSync::sync_objects(BL::Depsgraph &b_depsgraph,
         /* Skip in the motion case, as generating motion blur data will be handled in the
          * procedural. */
         if (!motion) {
-          sync_procedural(b_ob, b_mesh_cache);
+          sync_procedural(b_ob, b_mesh_cache, has_subdivision_modifier);
         }
       }
       else

intern/cycles/blender/blender_sync.h

@@ -151,7 +151,9 @@ class BlenderSync {
                       TaskPool *geom_task_pool);
   void sync_object_motion_init(BL::Object &b_parent, BL::Object &b_ob, Object *object);
 
-  void sync_procedural(BL::Object &b_ob, BL::MeshSequenceCacheModifier &b_mesh_cache);
+  void sync_procedural(BL::Object &b_ob,
+                       BL::MeshSequenceCacheModifier &b_mesh_cache,
+                       bool has_subdivision);
 
   bool sync_object_attributes(BL::DepsgraphObjectInstance &b_instance, Object *object);
 

intern/cycles/blender/blender_util.h

@@ -573,7 +573,8 @@ static inline BL::FluidDomainSettings object_fluid_gas_domain_find(BL::Object &b
 }
 
 static inline BL::MeshSequenceCacheModifier object_mesh_cache_find(BL::Object &b_ob,
-                                                                   bool check_velocity)
+                                                                   bool check_velocity,
+                                                                   bool *has_subdivision_modifier)
 {
   for (int i = b_ob.modifiers.length() - 1; i >= 0; --i) {
     BL::Modifier b_mod = b_ob.modifiers[i];
@@ -595,6 +596,15 @@ static inline BL::MeshSequenceCacheModifier object_mesh_cache_find(BL::Object &b
       continue;
     }
 
+    /* Only skip the subsurf modifier if we are not checking for the mesh sequence cache modifier
+     * for motion blur. */
+    if (b_mod.type() == BL::Modifier::type_SUBSURF && !check_velocity) {
+      if (has_subdivision_modifier) {
+        *has_subdivision_modifier = true;
+      }
+      continue;
+    }
+
     break;
   }
 

intern/cycles/render/alembic.cpp

@@ -385,6 +385,8 @@ NODE_DEFINE(AlembicObject)
   SOCKET_STRING(path, "Alembic Path", ustring());
   SOCKET_NODE_ARRAY(used_shaders, "Used Shaders", Shader::get_node_type());
 
+  SOCKET_BOOLEAN(ignore_subdivision, "Ignore Subdivision", true);
+
   SOCKET_INT(subd_max_level, "Max Subdivision Level", 1);
   SOCKET_FLOAT(subd_dicing_rate, "Subdivision Dicing Rate", 1.0f);
 
@@ -470,6 +472,33 @@ void AlembicObject::load_data_in_cache(CachedData &cached_data,
 
   cached_data.clear();
 
+  if (this->get_ignore_subdivision()) {
+    PolyMeshSchemaData data;
+    data.topology_variance = schema.getTopologyVariance();
+    data.time_sampling = schema.getTimeSampling();
+    data.positions = schema.getPositionsProperty();
+    data.face_counts = schema.getFaceCountsProperty();
+    data.face_indices = schema.getFaceIndicesProperty();
+    data.num_samples = schema.getNumSamples();
+    data.velocities = schema.getVelocitiesProperty();
+    data.shader_face_sets = parse_face_sets_for_shader_assignment(schema, get_used_shaders());
+
+    read_geometry_data(proc, cached_data, data, progress);
+
+    if (progress.get_cancel()) {
+      return;
+    }
+
+    /* Use the schema as the base compound property to also be able to look for top level
+     * properties. */
+    read_attributes(
+        proc, cached_data, schema, schema.getUVsParam(), get_requested_attributes(), progress);
+
+    cached_data.invalidate_last_loaded_time(true);
+    data_loaded = true;
+    return;
+  }
+
   SubDSchemaData data;
   data.time_sampling = schema.getTimeSampling();
   data.num_samples = schema.getNumSamples();
@@ -781,6 +810,19 @@ void AlembicProcedural::generate(Scene *scene, Progress &progress)
 
   const chrono_t frame_time = (chrono_t)((frame - frame_offset) / frame_rate);
 
+  /* Clear the subdivision caches as the data is stored differently. */
+  for (Node *node : objects) {
+    AlembicObject *object = static_cast<AlembicObject *>(node);
+
+    if (object->schema_type != AlembicObject::SUBD) {
+      continue;
+    }
+
+    if (object->ignore_subdivision_is_modified()) {
+      object->clear_cache();
+    }
+  }
+
   build_caches(progress);
 
   foreach (Node *node, objects) {
@@ -967,13 +1009,13 @@ void AlembicProcedural::read_mesh(AlembicObject *abc_object, Abc::chrono_t frame
 
 void AlembicProcedural::read_subd(AlembicObject *abc_object, Abc::chrono_t frame_time)
 {
-  CachedData &cached_data = abc_object->get_cached_data();
-
-  if (abc_object->subd_max_level_is_modified() || abc_object->subd_dicing_rate_is_modified()) {
-    /* need to reset the current data is something changed */
-    cached_data.invalidate_last_loaded_time();
+  if (abc_object->get_ignore_subdivision()) {
+    read_mesh(abc_object, frame_time);
+    return;
   }
 
+  CachedData &cached_data = abc_object->get_cached_data();
+
   /* Update sockets. */
 
   Object *object = abc_object->get_object();
@@ -988,6 +1030,11 @@ void AlembicProcedural::read_subd(AlembicObject *abc_object, Abc::chrono_t frame
     return;
   }
 
+  if (abc_object->subd_max_level_is_modified() || abc_object->subd_dicing_rate_is_modified()) {
+    /* need to reset the current data is something changed */
+    cached_data.invalidate_last_loaded_time();
+  }
+
   Mesh *mesh = static_cast<Mesh *>(object->get_geometry());
 
   /* Make sure shader ids are also updated. */

intern/cycles/render/alembic.h

@@ -353,6 +353,10 @@ class AlembicObject : public Node {
   /* Shaders used for rendering. */
   NODE_SOCKET_API_ARRAY(array<Node *>, used_shaders)
 
+  /* Treat this subdivision object as a regular polygon mesh, so no subdivision will be performed.
+   */
+  NODE_SOCKET_API(bool, ignore_subdivision)
+
   /* Maximum number of subdivisions for ISubD objects. */
   NODE_SOCKET_API(int, subd_max_level)
 
@@ -416,6 +420,11 @@ class AlembicObject : public Node {
     return cached_data_.is_constant();
   }
 
+  void clear_cache()
+  {
+    cached_data_.clear();
+  }
+
   Object *object = nullptr;
 
   bool data_loaded = false;