Alembic: add support for reading override layers

Override layers are a standard feature of Alembic, where archives can override
data from other archives, provided that the hierarchies match.

This is useful for modifying a UV map, updating an animation, or even creating
some sort of LOD system where low resolution meshes are swapped by high resolution
versions.

It is possible to add UV maps and vertex colors using this system, however, they
will only appear in the spreadsheet editor when viewing evaluated data, as the UV
map and Vertex color UI only show data present on the original mesh.

Implementation wise, this adds a `CacheFileLayer` data structure to the `CacheFile`
DNA, as well as some operators and UI to present and manage the layers. For both
the Alembic importer and the Cycles procedural, the main change is creating an
archive from a list of filepaths, instead of a single one.

After importing the base file through the regular import operator, layers can be added
to or removed from the `CacheFile` via the UI list under the `Override Layers` panel
located in the Mesh Sequence Cache modifier. Layers can also be moved around or
hidden.

See differential page for tests files and demos.

Reviewed by: brecht, sybren

Differential Revision: https://developer.blender.org/D13603

1 files changed, 166 insertions, 2 deletions

diff --git a/source/blender/editors/io/io_cache.c b/source/blender/editors/io/io_cache.c
index bf20c1f6438..4f71a804986 100644
--- a/source/blender/editors/io/io_cache.c
+++ b/source/blender/editors/io/io_cache.c
@@ -26,6 +26,7 @@
 #include "DNA_cachefile_types.h"
 #include "DNA_space_types.h"
 
+#include "BLI_listbase.h"
 #include "BLI_path_util.h"
 #include "BLI_string.h"
 
@@ -36,6 +37,7 @@
 #include "BKE_report.h"
 
 #include "RNA_access.h"
+#include "RNA_define.h"
 
 #include "DEG_depsgraph.h"
 
@@ -46,6 +48,12 @@
 
 #include "io_cache.h"
 
+static void reload_cachefile(bContext *C, CacheFile *cache_file)
+{
+  Depsgraph *depsgraph = CTX_data_ensure_evaluated_depsgraph(C);
+  BKE_cachefile_reload(depsgraph, cache_file);
+}
+
 static void cachefile_init(bContext *C, wmOperator *op)
 {
   PropertyPointerRNA *pprop;
@@ -146,8 +154,7 @@ static int cachefile_reload_exec(bContext *C, wmOperator *UNUSED(op))
     return OPERATOR_CANCELLED;
   }
 
-  Depsgraph *depsgraph = CTX_data_ensure_evaluated_depsgraph(C);
-  BKE_cachefile_reload(depsgraph, cache_file);
+  reload_cachefile(C, cache_file);
 
   return OPERATOR_FINISHED;
 }
@@ -164,3 +171,160 @@ void CACHEFILE_OT_reload(wmOperatorType *ot)
   /* flags */
   ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
 }
+
+/* ***************************** Add Layer Operator **************************** */
+
+static int cachefile_layer_open_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+  if (!RNA_struct_property_is_set(op->ptr, "filepath")) {
+    char filepath[FILE_MAX];
+    Main *bmain = CTX_data_main(C);
+
+    BLI_strncpy(filepath, BKE_main_blendfile_path(bmain), sizeof(filepath));
+    BLI_path_extension_replace(filepath, sizeof(filepath), ".abc");
+    RNA_string_set(op->ptr, "filepath", filepath);
+  }
+
+  /* There is no more CacheFile set when returning from the file selector, so store it here. */
+  op->customdata = CTX_data_edit_cachefile(C);
+
+  WM_event_add_fileselect(C, op);
+
+  return OPERATOR_RUNNING_MODAL;
+
+  UNUSED_VARS(event);
+}
+
+static int cachefile_layer_add_exec(bContext *C, wmOperator *op)
+{
+  if (!RNA_struct_property_is_set(op->ptr, "filepath")) {
+    BKE_report(op->reports, RPT_ERROR, "No filename given");
+    return OPERATOR_CANCELLED;
+  }
+
+  CacheFile *cache_file = op->customdata;
+
+  if (!cache_file) {
+    return OPERATOR_CANCELLED;
+  }
+
+  char filename[FILE_MAX];
+  RNA_string_get(op->ptr, "filepath", filename);
+
+  CacheFileLayer *layer = BKE_cachefile_add_layer(cache_file, filename);
+
+  if (!layer) {
+    WM_report(RPT_ERROR, "Could not add a layer to the cache file");
+    return OPERATOR_CANCELLED;
+  }
+
+  reload_cachefile(C, cache_file);
+  WM_main_add_notifier(NC_OBJECT | ND_DRAW, NULL);
+  return OPERATOR_FINISHED;
+}
+
+void CACHEFILE_OT_layer_add(wmOperatorType *ot)
+{
+  ot->name = "Add layer";
+  ot->description = "Add an override layer to the archive";
+  ot->idname = "CACHEFILE_OT_layer_add";
+
+  /* api callbacks */
+  ot->invoke = cachefile_layer_open_invoke;
+  ot->exec = cachefile_layer_add_exec;
+
+  WM_operator_properties_filesel(ot,
+                                 FILE_TYPE_ALEMBIC | FILE_TYPE_FOLDER,
+                                 FILE_BLENDER,
+                                 FILE_OPENFILE,
+                                 WM_FILESEL_FILEPATH | WM_FILESEL_RELPATH,
+                                 FILE_DEFAULTDISPLAY,
+                                 FILE_SORT_DEFAULT);
+}
+
+/* ***************************** Remove Layer Operator **************************** */
+
+static int cachefile_layer_remove_exec(bContext *C, wmOperator *UNUSED(op))
+{
+  CacheFile *cache_file = CTX_data_edit_cachefile(C);
+
+  if (!cache_file) {
+    return OPERATOR_CANCELLED;
+  }
+
+  CacheFileLayer *layer = BKE_cachefile_get_active_layer(cache_file);
+  BKE_cachefile_remove_layer(cache_file, layer);
+
+  reload_cachefile(C, cache_file);
+  WM_main_add_notifier(NC_OBJECT | ND_DRAW, NULL);
+  return OPERATOR_FINISHED;
+}
+
+void CACHEFILE_OT_layer_remove(wmOperatorType *ot)
+{
+  ot->name = "Add layer";
+  ot->description = "Remove an override layer to the archive";
+  ot->idname = "CACHEFILE_OT_layer_remove";
+
+  /* api callbacks */
+  ot->exec = cachefile_layer_remove_exec;
+
+  /* flags */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
+}
+
+/* ***************************** Move Layer Operator **************************** */
+
+static int cachefile_layer_move_exec(bContext *C, wmOperator *op)
+{
+  CacheFile *cache_file = CTX_data_edit_cachefile(C);
+
+  if (!cache_file) {
+    return OPERATOR_CANCELLED;
+  }
+
+  CacheFileLayer *layer = BKE_cachefile_get_active_layer(cache_file);
+
+  if (!layer) {
+    return OPERATOR_CANCELLED;
+  }
+
+  const int dir = RNA_enum_get(op->ptr, "direction");
+
+  if (BLI_listbase_link_move(&cache_file->layers, layer, dir)) {
+    cache_file->active_layer = BLI_findindex(&cache_file->layers, layer) + 1;
+    /* Only reload if something moved, might be expensive. */
+    reload_cachefile(C, cache_file);
+    WM_main_add_notifier(NC_OBJECT | ND_DRAW, NULL);
+  }
+
+  return OPERATOR_FINISHED;
+}
+
+void CACHEFILE_OT_layer_move(wmOperatorType *ot)
+{
+  static const EnumPropertyItem layer_slot_move[] = {
+      {-1, "UP", 0, "Up", ""},
+      {1, "DOWN", 0, "Down", ""},
+      {0, NULL, 0, NULL, NULL},
+  };
+
+  ot->name = "Move layer";
+  ot->description =
+      "Move layer in the list, layers further down the list will overwrite data from the layers "
+      "higher up";
+  ot->idname = "CACHEFILE_OT_layer_move";
+
+  /* api callbacks */
+  ot->exec = cachefile_layer_move_exec;
+
+  /* flags */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
+
+  RNA_def_enum(ot->srna,
+               "direction",
+               layer_slot_move,
+               0,
+               "Direction",
+               "Direction to move the active vertex group towards");
+}