Volumes: add volume.grids.frame_filepath to get the current frame filepath

This can be used by external renderers that can load OpenVDB files.

source/blender/blenkernel/BKE_volume.h

@@ -85,6 +85,7 @@ bool BKE_volume_is_loaded(const struct Volume *volume);
 
 int BKE_volume_num_grids(const struct Volume *volume);
 const char *BKE_volume_grids_error_msg(const struct Volume *volume);
+const char *BKE_volume_grids_frame_filepath(const struct Volume *volume);
 VolumeGrid *BKE_volume_grid_get(const struct Volume *volume, int grid_index);
 VolumeGrid *BKE_volume_grid_active_get(const struct Volume *volume);
 VolumeGrid *BKE_volume_grid_find(const struct Volume *volume, const char *name);

source/blender/blenkernel/intern/volume.cc

@@ -901,6 +901,16 @@ const char *BKE_volume_grids_error_msg(const Volume *volume)
 #endif
 }
 
+const char *BKE_volume_grids_frame_filepath(const Volume *volume)
+{
+#ifdef WITH_OPENVDB
+  return volume->runtime.grids->filepath;
+#else
+  UNUSED_VARS(volume);
+  return "";
+#endif
+}
+
 VolumeGrid *BKE_volume_grid_get(const Volume *volume, int grid_index)
 {
 #ifdef WITH_OPENVDB

source/blender/makesrna/intern/rna_volume.c

@@ -194,6 +194,19 @@ static int rna_VolumeGrids_error_message_length(PointerRNA *ptr)
   return strlen(BKE_volume_grids_error_msg(volume));
 }
 
+/* Frame Filepath */
+static void rna_VolumeGrids_frame_filepath_get(PointerRNA *ptr, char *value)
+{
+  Volume *volume = (Volume *)ptr->data;
+  strcpy(value, BKE_volume_grids_frame_filepath(volume));
+}
+
+static int rna_VolumeGrids_frame_filepath_length(PointerRNA *ptr)
+{
+  Volume *volume = (Volume *)ptr->data;
+  return strlen(BKE_volume_grids_frame_filepath(volume));
+}
+
 #else
 
 static void rna_def_volume_grid(BlenderRNA *brna)
@@ -308,6 +321,16 @@ static void rna_def_volume_grids(BlenderRNA *brna, PropertyRNA *cprop)
                            "Frame number that volume grids will be loaded at, based on scene time "
                            "and volume parameters");
 
+  prop = RNA_def_property(srna, "frame_filepath", PROP_STRING, PROP_FILEPATH);
+  RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+  RNA_def_property_string_funcs(
+      prop, "rna_VolumeGrids_frame_filepath_get", "rna_VolumeGrids_frame_filepath_length", NULL);
+
+  RNA_def_property_ui_text(prop,
+                           "Frame File Path",
+                           "Volume file used for loading the volume at the current frame. Empty "
+                           "if the volume has not be loaded or the frame only exists in memory");
+
   /* API */
   FunctionRNA *func;
   PropertyRNA *parm;
@@ -446,7 +469,7 @@ static void rna_def_volume(BlenderRNA *brna)
   /* File */
   prop = RNA_def_property(srna, "filepath", PROP_STRING, PROP_FILEPATH);
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
-  RNA_def_property_ui_text(prop, "File Path", "Volume sample file used by this Volume data-block");
+  RNA_def_property_ui_text(prop, "File Path", "Volume file used by this Volume data-block");
   RNA_def_property_update(prop, 0, "rna_Volume_update_filepath");
 
   prop = RNA_def_property(srna, "packed_file", PROP_POINTER, PROP_NONE);