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

1 files changed, 6 insertions, 2 deletions

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);