New functionality to export armatures and shape keys as USD
skeletons and blend shapes.

- Added Armature and Shape Key USD export options.
- Added USDArmatureWriter class.
- Extended USDMeshWriter to write skinned meshes for binding
with skeletons and 'neutral' meshes with blend shape targets.
- Added ModifierDisabler class to Temporarily disable armature
modifiers on mesh objects, so that meshes can be exported in
their rest position
- Added USDHierarchyIterator::process_usd_skel() function to
finish processing skeleton and blend shape export after the
writer instances completed writing.

@@ -0,0 +14,4 @@
+#include "WM_api.hh"
+
+/* Recursively invoke the 'visitor' function on the given bone and its children. */
+static void visit_bones(const Bone *bone, std::function<void(const Bone *)> visitor)

@@ -0,0 +22,4 @@
+
+  visitor(bone);
+
+  for (Bone *child = (Bone *)bone->childbase.first; child; child = child->next) {

@@ -0,0 +29,4 @@
+
+/* Return the armature modifier on the given object.  Return null if no
+ * armature modifier can be found. */
+static ArmatureModifierData *get_armature_modifier(const Object *obj)

@@ -0,0 +59,4 @@
+  return BKE_modifier_is_enabled(scene, mod, mode) ? mod : nullptr;
+}
+
+namespace blender::io::usd {

@@ -0,0 +74,4 @@
+  }
+}
+
+void get_armature_bone_names(const Object *ob_arm, std::vector<std::string> &r_names)

@@ -0,0 +77,4 @@
+void get_armature_bone_names(const Object *ob_arm, std::vector<std::string> &r_names)
+{
+  auto visitor = [&r_names](const Bone *bone) {
+    if (bone) {

@@ -0,0 +147,4 @@
+    return false;
+  }
+
+  bArmature *arm = (bArmature *)arm_mod->object->data;

@@ -0,0 +78,4 @@
+ * Attempt to add the given name to the 'names' set as a unique entry, modifying
+ * the name with a numerical suffix if necessary, and return the unique name that
+ * was added to the set. */
+std::string add_unique_name(std::set<std::string> &names, const std::string &name)

@@ -0,0 +188,4 @@
+
+const Key *get_mesh_shape_key(const Object *obj)
+{
+  if (!obj || !obj->data || obj->type != OB_MESH) {

@@ -0,0 +239,4 @@
+    }
+
+    if (kb == basis_key) {
+      // Skip the basis.

@@ -0,0 +401,4 @@
+    return;
+  }
+
+  std::vector<BlendShapeMergeInfo> merge_info;

@@ -0,0 +534,4 @@
+  }
+
+  /* Make a copy of the mesh so we can update the verts to the basis shape. */
+  Mesh *temp_mesh = reinterpret_cast<Mesh *>(

@@ -1038,0 +1241,4 @@
+                         const pxr::UsdSkelBindingAPI &skel_api,
+                         const std::vector<std::string> &bone_names)
+{
+  if (!mesh || !skel_api) {

@@ -1038,0 +1252,4 @@
+  std::vector<int> joint_index;
+
+  /* Build the index mapping. */
+  for (const bDeformGroup *def = (const bDeformGroup *)mesh->vertex_group_names.first; def;

@@ -1038,0 +1271,4 @@
+    return;
+  }
+
+  const blender::Span<MDeformVert> dverts = mesh->deform_verts();

@@ -1038,0 +1295,4 @@
+  /* Record number of out of bounds vert group indices, for error reporting. */
+  int num_out_of_bounds = 0;
+
+  for (const int i : dverts.index_range()) {

@@ -1038,0 +1304,4 @@
+    for (int j = 0; j < element_size; ++j, ++offset) {
+
+      if (offset >= joint_indices.size()) {
+        printf("Programmer error: out of bounds joint indices array offset.\n");

@@ -1038,0 +1315,4 @@
+      int def_nr = static_cast<int>(vert.dw[j].def_nr);
+
+      /* This out of bounds check is necessary because MDeformVert.totweight can be
+       * larger than the number of bDeformGroup structs in Object.defbase. It appears to be

@@ -0,0 +16,4 @@
+namespace blender::io::usd {
+
+/* Recursively invoke the 'visitor' function on the given bone and its children. */
+static void visit_bones(const Bone *bone, blender::FunctionRef<void(const Bone *)> visitor)

@@ -0,0 +62,4 @@
+static const ArmatureModifierData *get_armature_modifier(const Object *obj,
+                                                         const Depsgraph *depsgraph)
+{
+  BLI_assert(obj);

@@ -0,0 +130,4 @@
+                                    const char *name,
+                                    const Depsgraph *depsgraph)
+{
+  if (!obj || !name) {

@@ -0,0 +153,4 @@
+  return mods.size() == 1 && mods.first()->type == eModifierType_Armature;
+}
+
+Vector<ModifierData *> get_enabled_modifiers(const Object *obj, const Depsgraph *depsgraph)

@@ -0,0 +273,4 @@
+      /* Subtract the key positions from the
+       * basis positions to get the offsets. */
+      sub_v3_v3v3(offsets[i].data(), fp[i], basis_fp[i]);
+      indices[i] = i;

@@ -0,0 +407,4 @@
+
+  Vector<BlendShapeMergeInfo> merge_info;
+
+  /* We are merging blend shape names and weighs from multiple

@@ -0,0 +521,4 @@
+
+  /* If we're exporting blend shapes, we export the unmodified mesh with
+   * the verts in the basis key positions. */
+  Mesh *mesh = BKE_object_get_pre_modified_mesh(obj);

@@ -0,0 +3,4 @@
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include <map>

@@ -8,2 +8,4 @@
 #include "usd_exporter_context.h"
+#include "usd_skel_convert.h"
 
+#include <map>

@@ -1009,1 +1063,4 @@
     if (!BKE_object_defgroup_find_name(mesh_obj, joint_name.c_str())) {
+      /* If there is an attribute with the same name, remove it. */
+      bke::AttributeIDRef attr_id(joint_name);
+      if (attributes.contains(attr_id)) {

@@ -1038,0 +1174,4 @@
+void shape_key_export_chaser(pxr::UsdStageRefPtr stage,
+                             const ObjExportMap &shape_key_mesh_export_map)
+{
+  std::map<pxr::SdfPath, pxr::SdfPathSet> skel_to_mesh;

@@ -0,0 +5,4 @@
+
+#include "usd_writer_abstract.h"
+
+#include <string>

@@ -108,0 +132,4 @@
+             usd_export_context_.export_params.export_shapekeys) &&
+            attribute_id.name().rfind("skel:") == 0)
+        {
+          /* If we're exporting armatures ot shape keys to UsdSkel, we skip any

@@ -714,0 +902,4 @@
+
+Mesh *USDMeshWriter::get_export_mesh(Object *object_eval, bool &r_needsfree)
+{
+  if (write_blend_shapes_) {

@@ -47,6 +47,9 @@ struct USDExportParams {
   bool export_normals = true;
   bool export_mesh_colors = true;
   bool export_materials = true;
+  bool export_armatures;

@@ -338,0 +359,4 @@
+                  "skinned meshes");
+
+  RNA_def_boolean(ot->srna,
+                  "use_deform",

@@ -0,0 +175,4 @@
+    }
+
+    const bool deform = !(bone->flag & BONE_NO_DEFORM);
+    if (deform && deform_map) {

@@ -0,0 +184,4 @@
+
+  /* Get deform parents */
+  for (const auto &item : deform_map->items()) {
+    if (item.value) {

@@ -0,0 +186,4 @@
+  for (const auto &item : deform_map->items()) {
+    if (item.value) {
+      const Bone *parent = item.value->parent;
+      while (parent) {

@@ -0,0 +108,4 @@
+  pxr::UsdSkelBindingAPI skel_api = pxr::UsdSkelBindingAPI::Apply(mesh_prim);
+
+  if (!skel_api) {
+    CLOG_WARN(&LOG,

@@ -0,0 +513,4 @@
+      pxr::VtFloatArray src_weights;
+      if (info.src_weights_attr.Get(&src_weights, time)) {
+        if (!info.anim_map.Remap(src_weights, &dst_weights)) {
+          std::cerr << "WARNING: Failed remapping blend shape weights." << std::endl;

@@ -0,0 +109,4 @@
+
+    if (pxr::UsdGeomXform xf = get_xform_ancestor(prim, skel.GetPrim())) {
+      /* We found a common Xform ancestor, so we set its type to UsdSkelRoot. */
+      BKE_reportf(reports,

@@ -0,0 +113,4 @@
+  LISTBASE_FOREACH (const bPoseChannel *, pchan, &pose->chanbase) {
+
+    if (!pchan->bone) {
+      printf("WARNING: pchan %s is missing bone.\n", pchan->name);

@@ -0,0 +173,4 @@
+    return;
+  }
+
+  Map<const char *, const Bone *> *use_deform = usd_export_context_.export_params.use_deform ?

@@ -0,0 +70,4 @@
+
+  bArmature *armature = (bArmature *)ob_arm->data;
+
+  for (Bone *bone = (Bone *)armature->bonebase.first; bone; bone = bone->next) {

@@ -0,0 +79,4 @@
+                             const bool use_deform,
+                             Vector<std::string> &r_names)
+{
+  Map<const char *, const Bone *> deform_map;

@@ -0,0 +112,4 @@
+                        const Object *obj,
+                        const Map<const char *, const Bone *> *deform_map)
+{
+  if (!(skel_anim && obj && obj->pose)) {

@@ -0,0 +346,4 @@
+  pxr::VtTokenArray blendshape_names;
+
+  LISTBASE_FOREACH (KeyBlock *, kb, &key->block) {
+    if (!kb) {

@@ -51,0 +61,4 @@
+static const pxr::TfToken Anim("Anim", pxr::TfToken::Immortal);
+static const pxr::TfToken joint1("joint1", pxr::TfToken::Immortal);
+static const pxr::TfToken Skel("Skel", pxr::TfToken::Immortal);
+}  // namespace usdtokens

@@ -830,0 +947,4 @@
+      free_export_mesh(mesh);
+    }
+  }
+  catch (...) {