[Bf-blender-cvs] [85172cb5e10] universal-scene-description: USD Export: Armature export improvements.

[Michael Kowalski]

Commit: 85172cb5e10a86994bfa1fea846e49b21a91d643
Author: Michael Kowalski
Date:   Mon Nov 8 16:38:11 2021 -0500
Branches: universal-scene-description
https://developer.blender.org/rB85172cb5e10a86994bfa1fea846e49b21a91d643

USD Export:  Armature export improvements.

Now including the root prim in the skinned mesh
skeleton relationship path.  Also, added logic to
avoid nesting SkelRoot prims in the USD, as such
nesting causes skeleton binding to fail as well
as crashes in Create.

Now iterating over the deform groups of the
evaluated mesh when setting joint weights
and indices, to ensure the vertex group
data is valid.

===================================================================

M	source/blender/io/usd/intern/usd_writer_skel_root.cc
M	source/blender/io/usd/intern/usd_writer_skel_root.h
M	source/blender/io/usd/intern/usd_writer_skinned_mesh.cc

===================================================================

diff --git a/source/blender/io/usd/intern/usd_writer_skel_root.cc b/source/blender/io/usd/intern/usd_writer_skel_root.cc
index e31bab08ba2..82a291f5dc6 100644
--- a/source/blender/io/usd/intern/usd_writer_skel_root.cc
+++ b/source/blender/io/usd/intern/usd_writer_skel_root.cc
@@ -22,12 +22,47 @@
 
 namespace blender::io::usd {
 
+bool USDSkelRootWriter::is_under_skel_root() const
+{
+  pxr::SdfPath parent_path(usd_export_context_.usd_path);
+
+  parent_path = parent_path.GetParentPath();
+
+  if (parent_path.IsEmpty()) {
+    return false;
+  }
+
+  pxr::UsdPrim prim = usd_export_context_.stage->GetPrimAtPath(parent_path);
+
+  while (prim.IsValid()) {
+    if (prim.IsA<pxr::UsdSkelRoot>()) {
+      return true;
+    }
+    prim = prim.GetParent();
+  }
+
+  return false;
+}
+
 pxr::UsdGeomXformable USDSkelRootWriter::create_xformable() const
 {
-  pxr::UsdSkelRoot root =
+  /* Create a UsdSkelRoot primitive, unless this prim is already
+    beneath a UsdSkelRoot, in which case create an Xform. */
+
+  pxr::UsdGeomXformable root;
+
+  if (is_under_skel_root()) {
+    root =
+      (usd_export_context_.export_params.export_as_overs) ?
+      pxr::UsdGeomXform(usd_export_context_.stage->OverridePrim(usd_export_context_.usd_path)) :
+      pxr::UsdGeomXform::Define(usd_export_context_.stage, usd_export_context_.usd_path);
+  }
+  else {
+    root =
       (usd_export_context_.export_params.export_as_overs) ?
-          pxr::UsdSkelRoot(usd_export_context_.stage->OverridePrim(usd_export_context_.usd_path)) :
-          pxr::UsdSkelRoot::Define(usd_export_context_.stage, usd_export_context_.usd_path);
+      pxr::UsdSkelRoot(usd_export_context_.stage->OverridePrim(usd_export_context_.usd_path)) :
+      pxr::UsdSkelRoot::Define(usd_export_context_.stage, usd_export_context_.usd_path);
+  }
 
   return root;
 }
diff --git a/source/blender/io/usd/intern/usd_writer_skel_root.h b/source/blender/io/usd/intern/usd_writer_skel_root.h
index 4c61599715f..7a33721a79e 100644
--- a/source/blender/io/usd/intern/usd_writer_skel_root.h
+++ b/source/blender/io/usd/intern/usd_writer_skel_root.h
@@ -34,6 +34,10 @@ class USDSkelRootWriter : public USDTransformWriter {
  protected:
   /* Override to create UsdSkelRoot prim. */
   pxr::UsdGeomXformable create_xformable() const override;
+
+  /* Rturns true if the prim to be created is
+   * already unde a USD SkeRoot. */
+  bool is_under_skel_root() const;
 };
 
 }  // namespace blender::io::usd
diff --git a/source/blender/io/usd/intern/usd_writer_skinned_mesh.cc b/source/blender/io/usd/intern/usd_writer_skinned_mesh.cc
index 3f1b6c831a3..738f02ff272 100644
--- a/source/blender/io/usd/intern/usd_writer_skinned_mesh.cc
+++ b/source/blender/io/usd/intern/usd_writer_skinned_mesh.cc
@@ -136,6 +136,10 @@ void USDSkinnedMeshWriter::do_write(HierarchyContext &context)
     return;
   }
 
+  if (strlen(usd_export_context_.export_params.root_prim_path) != 0) {
+    skel_path = std::string(usd_export_context_.export_params.root_prim_path) + skel_path;
+  }
+
   usd_skel_api.CreateSkeletonRel().SetTargets(pxr::SdfPathVector({pxr::SdfPath(skel_path)}));
 
   if (pxr::UsdAttribute geom_bind_attr = usd_skel_api.CreateGeomBindTransformAttr()) {
@@ -186,7 +190,7 @@ void USDSkinnedMeshWriter::write_weights(const Object *ob,
 
   std::vector<int> group_to_bone_idx;
 
-  for (bDeformGroup *def = (bDeformGroup *)ob->defbase.first; def; def = def->next) {
+  for (const bDeformGroup *def = (const bDeformGroup *)mesh->vertex_group_names.first; def; def = def->next) {
 
     int bone_idx = -1;
     /* For now, n-squared search is acceptable. */