Geometry Nodes: Handle multiple grids in the volume to mesh node

In future use cases, a volume can contain many grids that represent the
density information. In this case, it's better if the volume to mesh node
creates a mesh based on all of the grids in the volume.

This is also a benefit to share-ability, since one doesn't have to
specify the grid name in the node. Instead, in the future we can have
a way to split particular grids into separate volumes, if only one
grid should be considered.

The code changes are relatively simple:
 - Move the old volume to mesh node to the legacy folder.
 - Run the volume to mesh node on all instance geometry, like elsewhere.
 - Make the blenkernel's volume to mesh API a bit more specific.

Differential Revision: https://developer.blender.org/D12997

1 files changed, 17 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/volume.cc b/source/blender/blenkernel/intern/volume.cc
index 7e7a40d8e9b..a72b5268e1d 100644
--- a/source/blender/blenkernel/intern/volume.cc
+++ b/source/blender/blenkernel/intern/volume.cc
@@ -36,6 +36,7 @@
 #include "BLI_math.h"
 #include "BLI_path_util.h"
 #include "BLI_string.h"
+#include "BLI_string_ref.hh"
 #include "BLI_task.hh"
 #include "BLI_utildefines.h"
 
@@ -71,6 +72,7 @@ static CLG_LogRef LOG = {"bke.volume"};
 using blender::float3;
 using blender::float4x4;
 using blender::IndexRange;
+using blender::StringRef;
 
 #ifdef WITH_OPENVDB
 #  include <atomic>
@@ -1451,6 +1453,21 @@ VolumeGrid *BKE_volume_grid_add(Volume *volume, const char *name, VolumeGridType
 #endif
 }
 
+#ifdef WITH_OPENVDB
+VolumeGrid *BKE_volume_grid_add_vdb(Volume &volume,
+                                    const StringRef name,
+                                    openvdb::GridBase::Ptr vdb_grid)
+{
+  VolumeGridVector &grids = *volume.runtime.grids;
+  BLI_assert(BKE_volume_grid_find_for_read(&volume, name.data()) == nullptr);
+  BLI_assert(BKE_volume_grid_type_openvdb(*vdb_grid) != VOLUME_GRID_UNKNOWN);
+
+  vdb_grid->setName(name);
+  grids.emplace_back(vdb_grid);
+  return &grids.back();
+}
+#endif
+
 void BKE_volume_grid_remove(Volume *volume, VolumeGrid *grid)
 {
 #ifdef WITH_OPENVDB