USD: add volume/VDB export

Add support for volume (OpenVDB) USD export:

- Allows to export both static and animated volumes.
- Supports volumes that have OpenVDB data from files or are generated in
  Blender with 'Mesh to Volume' modifier.
- For volumes that have generated data in Blender it also exports
  corresponding .vdb files. Those files are saved in a new folder named
  "volumes".
- Slightly changes the USD export UI panel. "Relative Texture Paths"
  becomes "Relative Paths" (and has separate UI box) as the
  functionality will now apply to both textures and volumes. Disabling
  of this option due to "Materials" checkbox being turned off has been
  removed.

Reviewed By: sybren, makowalski

Differential Revision: https://developer.blender.org/D14193

Manifest Task: T95407

3 files changed, 8 insertions, 5 deletions

diff --git a/source/blender/io/common/IO_abstract_hierarchy_iterator.h b/source/blender/io/common/IO_abstract_hierarchy_iterator.h
index 3c6b6cc631e..3371501db95 100644
--- a/source/blender/io/common/IO_abstract_hierarchy_iterator.h
+++ b/source/blender/io/common/IO_abstract_hierarchy_iterator.h
@@ -30,6 +30,7 @@
 struct Depsgraph;
 struct DupliObject;
 struct ID;
+struct Main;
 struct Object;
 struct ParticleSystem;
 
@@ -204,12 +205,13 @@ class AbstractHierarchyIterator {
  protected:
   ExportGraph export_graph_;
   ExportPathMap duplisource_export_path_;
+  Main *bmain_;
   Depsgraph *depsgraph_;
   WriterMap writers_;
   ExportSubset export_subset_;
 
  public:
-  explicit AbstractHierarchyIterator(Depsgraph *depsgraph);
+  explicit AbstractHierarchyIterator(Main *bmain, Depsgraph *depsgraph);
   virtual ~AbstractHierarchyIterator();
 
   /* Iterate over the depsgraph, create writers, and tell the writers to write.
diff --git a/source/blender/io/common/intern/abstract_hierarchy_iterator.cc b/source/blender/io/common/intern/abstract_hierarchy_iterator.cc
index f0501d4cf62..82bb1c57833 100644
--- a/source/blender/io/common/intern/abstract_hierarchy_iterator.cc
+++ b/source/blender/io/common/intern/abstract_hierarchy_iterator.cc
@@ -161,8 +161,8 @@ bool AbstractHierarchyWriter::check_has_deforming_physics(const HierarchyContext
   return rbo != nullptr && rbo->type == RBO_TYPE_ACTIVE && (rbo->flag & RBO_FLAG_USE_DEFORM) != 0;
 }
 
-AbstractHierarchyIterator::AbstractHierarchyIterator(Depsgraph *depsgraph)
-    : depsgraph_(depsgraph), export_subset_({true, true})
+AbstractHierarchyIterator::AbstractHierarchyIterator(Main *bmain, Depsgraph *depsgraph)
+    : bmain_(bmain), depsgraph_(depsgraph), export_subset_({true, true})
 {
 }
 
diff --git a/source/blender/io/common/intern/abstract_hierarchy_iterator_test.cc b/source/blender/io/common/intern/abstract_hierarchy_iterator_test.cc
index 52cae89c2e8..81a3546259e 100644
--- a/source/blender/io/common/intern/abstract_hierarchy_iterator_test.cc
+++ b/source/blender/io/common/intern/abstract_hierarchy_iterator_test.cc
@@ -54,7 +54,8 @@ class TestingHierarchyIterator : public AbstractHierarchyIterator {
   used_writers hair_writers;
   used_writers particle_writers;
 
-  explicit TestingHierarchyIterator(Depsgraph *depsgraph) : AbstractHierarchyIterator(depsgraph)
+  explicit TestingHierarchyIterator(Main *bmain, Depsgraph *depsgraph)
+      : AbstractHierarchyIterator(bmain, depsgraph)
   {
   }
   ~TestingHierarchyIterator() override
@@ -105,7 +106,7 @@ class AbstractHierarchyIteratorTest : public BlendfileLoadingBaseTest {
   /* Create a test iterator. */
   void iterator_create()
   {
-    iterator = new TestingHierarchyIterator(depsgraph);
+    iterator = new TestingHierarchyIterator(bfile->main, depsgraph);
   }
   /* Free the test iterator if it is not nullptr. */
   void iterator_free()