Alembic: integrate cache file into the dependency graph

* The cache file datablock is now evaluated as part of the dependency graph,
  creating/freeing the Alembic file handle matching the current frame.
  Modifiers and constraints depend on this evaluation.
* Cache file handles and readers now only exist on COW datablocks, never the
  original ones.
* Object data paths are flushed back to the original for the user interface.
* The cache file keeps a list of all readers associated with its handle, and
  automatically frees them when the handle is freed. This kind of sharing of
  data across datablocks is weak but we have no better mechanism for it.

Fix T62720: Alembic sequences not working and crashing

Differential Revision: https://developer.blender.org/D4774

1 files changed, 16 insertions, 12 deletions

diff --git a/source/blender/modifiers/intern/MOD_meshsequencecache.c b/source/blender/modifiers/intern/MOD_meshsequencecache.c
index 7710082150b..760830ffb24 100644
--- a/source/blender/modifiers/intern/MOD_meshsequencecache.c
+++ b/source/blender/modifiers/intern/MOD_meshsequencecache.c
@@ -18,6 +18,11 @@
  * \ingroup modifiers
  */
 
+#include <string.h>
+
+#include "BLI_utildefines.h"
+#include "BLI_string.h"
+
 #include "DNA_cachefile_types.h"
 #include "DNA_mesh_types.h"
 #include "DNA_meshdata_types.h"
@@ -47,6 +52,9 @@ static void initData(ModifierData *md)
   mcmd->cache_file = NULL;
   mcmd->object_path[0] = '\0';
   mcmd->read_flag = MOD_MESHSEQ_READ_ALL;
+
+  mcmd->reader = NULL;
+  mcmd->reader_object_path[0] = '\0';
 }
 
 static void copyData(const ModifierData *md, ModifierData *target, const int flag)
@@ -59,6 +67,7 @@ static void copyData(const ModifierData *md, ModifierData *target, const int fla
   modifier_copyData_generic(md, target, flag);
 
   tmcmd->reader = NULL;
+  tmcmd->reader_object_path[0] = '\0';
 }
 
 static void freeData(ModifierData *md)
@@ -66,10 +75,8 @@ static void freeData(ModifierData *md)
   MeshSeqCacheModifierData *mcmd = (MeshSeqCacheModifierData *)md;
 
   if (mcmd->reader) {
-#ifdef WITH_ALEMBIC
-    CacheReader_free(mcmd->reader);
-#endif
-    mcmd->reader = NULL;
+    mcmd->reader_object_path[0] = '\0';
+    BKE_cachefile_reader_free(mcmd->cache_file, &mcmd->reader);
   }
 }
 
@@ -93,17 +100,14 @@ static Mesh *applyModifier(ModifierData *md, const ModifierEvalContext *ctx, Mes
   Mesh *org_mesh = mesh;
 
   Scene *scene = DEG_get_evaluated_scene(ctx->depsgraph);
+  CacheFile *cache_file = mcmd->cache_file;
   const float frame = DEG_get_ctime(ctx->depsgraph);
-  const float time = BKE_cachefile_time_offset(mcmd->cache_file, frame, FPS);
+  const float time = BKE_cachefile_time_offset(cache_file, frame, FPS);
   const char *err_str = NULL;
 
-  CacheFile *cache_file = (CacheFile *)DEG_get_original_id(&mcmd->cache_file->id);
-
-  BKE_cachefile_ensure_handle(G.main, cache_file);
-
-  if (!mcmd->reader) {
-    mcmd->reader = CacheReader_open_alembic_object(
-        cache_file->handle, NULL, ctx->object, mcmd->object_path);
+  if (!mcmd->reader || !STREQ(mcmd->reader_object_path, mcmd->object_path)) {
+    STRNCPY(mcmd->reader_object_path, mcmd->object_path);
+    BKE_cachefile_reader_open(cache_file, &mcmd->reader, ctx->object, mcmd->object_path);
     if (!mcmd->reader) {
       modifier_setError(md, "Could not create Alembic reader for file %s", cache_file->filepath);
       return mesh;