Cycles: experimental integration of Alembic procedural in viewport rendering

This patch exposes the Cycles Alembic Procedural through the MeshSequenceCache
modifier in order to use and test it from Blender.

To enable it, one has to switch the render feature set to experimental and
activate the Procedural in the modifier. An Alembic Procedural is then
created for each CacheFile from Blender set to use the Procedural, and each
Blender object having a MeshSequenceCache modifier is added to list of objects
of the right procedural.

The procedural's parameters derive from the CacheFile's properties which are
already exposed in the UI through the modifier, although more Cycles specific
options might be added in the future.

As there is currently no cache controls and since we load all the data at the
beginning of the render session, the procedural is only available during
viewport renders at the moment. When an Alembic procedural is rendered, data
from the archive are not read on the Blender side.

If a Cycles render is not active and the CacheFile is set to use the Cycles Procedural,
bounding boxes are used to display the objects in the scene as a signal that the
objects are not processed by Blender anymore. This is standard in other DCCs.
However this does not reduce the memory usage from Blender as the Alembic data
was already loaded either during an import or during a .blend file read.

This is mostly a hack to test the Cycles Alembic procedural until we have a
better Blender side mechanism for letting renderers load their own geometry,
which will be based on import and export settings on Collections (T68933).

Ref T79174, D3089

Reviewed By: brecht, sybren

Maniphest Tasks: T79174

Differential Revision: https://developer.blender.org/D10197

9 files changed, 72 insertions, 7 deletions

diff --git a/source/blender/blenkernel/BKE_cachefile.h b/source/blender/blenkernel/BKE_cachefile.h
index a6b2aa8540a..58d876b184b 100644
--- a/source/blender/blenkernel/BKE_cachefile.h
+++ b/source/blender/blenkernel/BKE_cachefile.h
@@ -32,6 +32,7 @@ struct CacheReader;
 struct Depsgraph;
 struct Main;
 struct Object;
+struct Scene;
 
 void BKE_cachefiles_init(void);
 void BKE_cachefiles_exit(void);
@@ -60,6 +61,15 @@ void BKE_cachefile_reader_open(struct CacheFile *cache_file,
                                const char *object_path);
 void BKE_cachefile_reader_free(struct CacheFile *cache_file, struct CacheReader **reader);
 
+/* Determine whether the CacheFile should use a render engine procedural. If so, data is not read
+ * from the file and bouding boxes are used to represent the objects in the Scene. Render engines
+ * will receive the bounding box as a placeholder but can instead load the data directly if they
+ * support it.
+ */
+bool BKE_cache_file_uses_render_procedural(const struct CacheFile *cache_file,
+                                           struct Scene *scene,
+                                           const int dag_eval_mode);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/source/blender/blenkernel/BKE_modifier.h b/source/blender/blenkernel/BKE_modifier.h
index 0b4e1191956..c5f309570cd 100644
--- a/source/blender/blenkernel/BKE_modifier.h
+++ b/source/blender/blenkernel/BKE_modifier.h
@@ -319,8 +319,10 @@ typedef struct ModifierTypeInfo {
    * changes.
    *
    * This function is optional (assumes false if not present).
+   *
+   * The dag_eval_mode should be of type eEvaluationMode.
    */
-  bool (*dependsOnTime)(struct ModifierData *md);
+  bool (*dependsOnTime)(struct Scene *scene, struct ModifierData *md, const int dag_eval_mode);
 
   /**
    * True when a deform modifier uses normals, the requiredDataMask
@@ -425,7 +427,9 @@ void BKE_modifier_copydata(struct ModifierData *md, struct ModifierData *target)
 void BKE_modifier_copydata_ex(struct ModifierData *md,
                               struct ModifierData *target,
                               const int flag);
-bool BKE_modifier_depends_ontime(struct ModifierData *md);
+bool BKE_modifier_depends_ontime(struct Scene *scene,
+                                 struct ModifierData *md,
+                                 int dag_eval_mode);
 bool BKE_modifier_supports_mapping(struct ModifierData *md);
 bool BKE_modifier_supports_cage(struct Scene *scene, struct ModifierData *md);
 bool BKE_modifier_couldbe_cage(struct Scene *scene, struct ModifierData *md);
diff --git a/source/blender/blenkernel/BKE_object.h b/source/blender/blenkernel/BKE_object.h
index 4724e6dfab6..a823602e341 100644
--- a/source/blender/blenkernel/BKE_object.h
+++ b/source/blender/blenkernel/BKE_object.h
@@ -401,7 +401,10 @@ void BKE_object_groups_clear(struct Main *bmain, struct Scene *scene, struct Obj
 
 struct KDTree_3d *BKE_object_as_kdtree(struct Object *ob, int *r_tot);
 
-bool BKE_object_modifier_use_time(struct Object *ob, struct ModifierData *md);
+bool BKE_object_modifier_use_time(struct Scene *scene,
+                                  struct Object *ob,
+                                  struct ModifierData *md,
+                                  int dag_eval_mode);
 
 bool BKE_object_modifier_update_subframe(struct Depsgraph *depsgraph,
                                          struct Scene *scene,
diff --git a/source/blender/blenkernel/BKE_scene.h b/source/blender/blenkernel/BKE_scene.h
index 6d58e165ea3..83ce5e72794 100644
--- a/source/blender/blenkernel/BKE_scene.h
+++ b/source/blender/blenkernel/BKE_scene.h
@@ -174,6 +174,10 @@ bool BKE_scene_uses_blender_eevee(const struct Scene *scene);
 bool BKE_scene_uses_blender_workbench(const struct Scene *scene);
 bool BKE_scene_uses_cycles(const struct Scene *scene);
 
+/* Return whether the Cycles experimental feature is enabled. It is invalid to call without first
+ * ensuring that Cycles is the active render engine (e.g. with BKE_scene_uses_cycles). */
+bool BKE_scene_uses_cycles_experimental_features(struct Scene *scene);
+
 void BKE_scene_copy_data_eevee(struct Scene *sce_dst, const struct Scene *sce_src);
 
 void BKE_scene_disable_color_management(struct Scene *scene);
diff --git a/source/blender/blenkernel/intern/cachefile.c b/source/blender/blenkernel/intern/cachefile.c
index 75180de94d8..8dd28c889f5 100644
--- a/source/blender/blenkernel/intern/cachefile.c
+++ b/source/blender/blenkernel/intern/cachefile.c
@@ -49,6 +49,8 @@
 
 #include "DEG_depsgraph_query.h"
 
+#include "RE_engine.h"
+
 #include "BLO_read_write.h"
 
 #ifdef WITH_ALEMBIC
@@ -409,3 +411,19 @@ float BKE_cachefile_time_offset(const CacheFile *cache_file, const float time, c
   const float frame = (cache_file->override_frame ? cache_file->frame : time);
   return cache_file->is_sequence ? frame : frame / fps - time_offset;
 }
+
+bool BKE_cache_file_uses_render_procedural(const CacheFile *cache_file,
+                                           Scene *scene,
+                                           const int dag_eval_mode)
+{
+  RenderEngineType *render_engine_type = RE_engines_find(scene->r.engine);
+
+  if (cache_file->type != CACHEFILE_TYPE_ALEMBIC ||
+      !RE_engine_supports_alembic_procedural(render_engine_type, scene)) {
+    return false;
+  }
+
+  /* The render time procedural is only enabled during viewport rendering. */
+  const bool is_final_render = (eEvaluationMode)dag_eval_mode == DAG_EVAL_RENDER;
+  return cache_file->use_render_procedural && !is_final_render;
+}
diff --git a/source/blender/blenkernel/intern/constraint.c b/source/blender/blenkernel/intern/constraint.c
index 4b26022039e..30aa22387d0 100644
--- a/source/blender/blenkernel/intern/constraint.c
+++ b/source/blender/blenkernel/intern/constraint.c
@@ -5430,6 +5430,11 @@ static void transformcache_evaluate(bConstraint *con, bConstraintOb *cob, ListBa
     return;
   }
 
+  /* Do not process data if using a render time procedural. */
+  if (BKE_cache_file_uses_render_procedural(cache_file, scene, DEG_get_mode(cob->depsgraph))) {
+    return;
+  }
+
   const float frame = DEG_get_ctime(cob->depsgraph);
   const float time = BKE_cachefile_time_offset(cache_file, frame, FPS);
 
diff --git a/source/blender/blenkernel/intern/modifier.c b/source/blender/blenkernel/intern/modifier.c
index 2088c4268e6..821ca7b98b3 100644
--- a/source/blender/blenkernel/intern/modifier.c
+++ b/source/blender/blenkernel/intern/modifier.c
@@ -249,11 +249,11 @@ bool BKE_modifier_unique_name(ListBase *modifiers, ModifierData *md)
   return false;
 }
 
-bool BKE_modifier_depends_ontime(ModifierData *md)
+bool BKE_modifier_depends_ontime(Scene *scene, ModifierData *md, const int dag_eval_mode)
 {
   const ModifierTypeInfo *mti = BKE_modifier_get_info(md->type);
 
-  return mti->dependsOnTime && mti->dependsOnTime(md);
+  return mti->dependsOnTime && mti->dependsOnTime(scene, md, dag_eval_mode);
 }
 
 bool BKE_modifier_supports_mapping(ModifierData *md)
diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index 23b9dca8371..86db4b6ace8 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -5411,9 +5411,12 @@ KDTree_3d *BKE_object_as_kdtree(Object *ob, int *r_tot)
   return tree;
 }
 
-bool BKE_object_modifier_use_time(Object *ob, ModifierData *md)
+bool BKE_object_modifier_use_time(Scene *scene,
+                                  Object *ob,
+                                  ModifierData *md,
+                                  const int dag_eval_mode)
 {
-  if (BKE_modifier_depends_ontime(md)) {
+  if (BKE_modifier_depends_ontime(scene, md, dag_eval_mode)) {
     return true;
   }
 
diff --git a/source/blender/blenkernel/intern/scene.c b/source/blender/blenkernel/intern/scene.c
index 5ecd9b7283e..3fe00adc4d5 100644
--- a/source/blender/blenkernel/intern/scene.c
+++ b/source/blender/blenkernel/intern/scene.c
@@ -109,6 +109,8 @@
 
 #include "RE_engine.h"
 
+#include "RNA_access.h"
+
 #include "SEQ_edit.h"
 #include "SEQ_iterator.h"
 #include "SEQ_modifier.h"
@@ -2938,6 +2940,22 @@ bool BKE_scene_uses_cycles(const Scene *scene)
   return STREQ(scene->r.engine, RE_engine_id_CYCLES);
 }
 
+/* This enumeration has to match the one defined in the Cycles addon. */
+typedef enum eCyclesFeatureSet {
+  CYCLES_FEATURES_SUPPORTED = 0,
+  CYCLES_FEATURES_EXPERIMENTAL = 1,
+} eCyclesFeatureSet;
+
+/* We cannot use const as RNA_id_pointer_create is not using a const ID. */
+bool BKE_scene_uses_cycles_experimental_features(Scene *scene)
+{
+  BLI_assert(BKE_scene_uses_cycles(scene));
+  PointerRNA scene_ptr;
+  RNA_id_pointer_create(&scene->id, &scene_ptr);
+  PointerRNA cycles_ptr = RNA_pointer_get(&scene_ptr, "cycles");
+  return RNA_enum_get(&cycles_ptr, "feature_set") == CYCLES_FEATURES_EXPERIMENTAL;
+}
+
 void BKE_scene_base_flag_to_objects(ViewLayer *view_layer)
 {
   Base *base = view_layer->object_bases.first;