usd_writer_armature.cc

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
#include "usd_writer_armature.hh"
#include "usd_armature_utils.hh"
 
#include "BKE_action.hh"
 
#include "DNA_armature_types.h"
 
#include <pxr/base/gf/matrix4d.h>
#include <pxr/base/gf/matrix4f.h>
#include <pxr/usd/usdGeom/primvarsAPI.h>
#include <pxr/usd/usdSkel/animation.h>
#include <pxr/usd/usdSkel/bindingAPI.h>
#include <pxr/usd/usdSkel/skeleton.h>
 
#include "CLG_log.h"
static CLG_LogRef LOG = {"io.usd"};
 
namespace usdtokens {
static const pxr::TfToken Anim("Anim", pxr::TfToken::Immortal);
}  // namespace usdtokens
 
static pxr::GfMatrix4d parent_relative_pose_mat(const bPoseChannel *pchan)
{
  /* Note that the float matrix will be returned as GfMatrix4d, because
   * USD requires doubles. */
  const pxr::GfMatrix4f pose_mat(pchan->pose_mat);
 
  if (pchan->parent) {
    const pxr::GfMatrix4f parent_pose_mat(pchan->parent->pose_mat);
    const pxr::GfMatrix4f xf = pose_mat * parent_pose_mat.GetInverse();
    return pxr::GfMatrix4d(xf);
  }
 
  /* No parent, so return the pose matrix directly. */
  return pxr::GfMatrix4d(pose_mat);
}
 
/* Initialize the given skeleton and animation from
 * the given armature object. */
static void initialize(const Object *obj,
                       pxr::UsdSkelSkeleton &skel,
                       pxr::UsdSkelAnimation &skel_anim,
                       const blender::Map<blender::StringRef, const Bone *> *deform_bones,
                       bool allow_unicode)
{
  using namespace blender::io::usd;
 
  pxr::VtTokenArray joints;
  pxr::VtArray<float> bone_lengths;
  pxr::VtArray<pxr::GfMatrix4d> bind_xforms;
  pxr::VtArray<pxr::GfMatrix4d> rest_xforms;
 
  /* Function to collect the bind and rest transforms from each bone. */
  auto visitor = [&](const Bone *bone) {
    if (!bone) {
      return;
    }
 
    if (deform_bones && !deform_bones->contains(bone->name)) {
      /* If deform_map is passed in, assume we're going deform-only.
       * Bones not found in the map should be skipped. */
      return;
    }
 
    /* Store Blender bone lengths to facilitate better round-tripping. */
    bone_lengths.push_back(bone->length);
 
    joints.push_back(build_usd_joint_path(bone, allow_unicode));
    const pxr::GfMatrix4f arm_mat(bone->arm_mat);
    bind_xforms.push_back(pxr::GfMatrix4d(arm_mat));
 
    /* Set the rest transform to the parent-relative pose matrix, or the parent-relative
     * armature matrix, if no pose channel exists. */
    if (const bPoseChannel *pchan = BKE_pose_channel_find_name(obj->pose, bone->name)) {
      rest_xforms.push_back(parent_relative_pose_mat(pchan));
    }
    else if (bone->parent) {
      pxr::GfMatrix4f parent_arm_mat(bone->parent->arm_mat);
      const pxr::GfMatrix4f rest_mat = arm_mat * parent_arm_mat.GetInverse();
      rest_xforms.push_back(pxr::GfMatrix4d(rest_mat));
    }
    else {
      rest_xforms.push_back(pxr::GfMatrix4d(arm_mat));
    }
  };
 
  visit_bones(obj, visitor);
  skel.GetJointsAttr().Set(joints);
  skel.GetBindTransformsAttr().Set(bind_xforms);
  skel.GetRestTransformsAttr().Set(rest_xforms);
 
  const pxr::UsdPrim skel_prim = skel.GetPrim();
 
  /* Store the custom bone lengths as just a regular Primvar attached to the Skeleton. */
  const pxr::UsdGeomPrimvarsAPI pv_api = pxr::UsdGeomPrimvarsAPI(skel_prim);
  pxr::UsdGeomPrimvar pv_lengths = pv_api.CreatePrimvar(
      BlenderBoneLengths, pxr::SdfValueTypeNames->FloatArray, pxr::UsdGeomTokens->uniform);
  pv_lengths.Set(bone_lengths);
 
  pxr::UsdSkelBindingAPI usd_skel_api = pxr::UsdSkelBindingAPI::Apply(skel_prim);
 
  if (skel_anim) {
    usd_skel_api.CreateAnimationSourceRel().SetTargets(
        pxr::SdfPathVector({pxr::SdfPath(usdtokens::Anim)}));
    create_pose_joints(skel_anim, *obj, deform_bones, allow_unicode);
  }
}
 
/* Add skeleton transform samples from the armature pose channels. */
static void add_anim_sample(pxr::UsdSkelAnimation &skel_anim,
                            const Object *obj,
                            const pxr::UsdTimeCode time,
                            const blender::Map<blender::StringRef, const Bone *> *deform_map)
{
  if (!(skel_anim && obj && obj->pose)) {
    return;
  }
 
  pxr::VtArray<pxr::GfMatrix4d> xforms;
 
  const bPose *pose = obj->pose;
 
  LISTBASE_FOREACH (const bPoseChannel *, pchan, &pose->chanbase) {
 
    BLI_assert(pchan->bone);
 
    if (deform_map && !deform_map->contains(pchan->bone->name)) {
      /* If deform_map is passed in, assume we're going deform-only.
       * Bones not found in the map should be skipped. */
      continue;
    }
 
    xforms.push_back(parent_relative_pose_mat(pchan));
  }
 
  skel_anim.SetTransforms(xforms, time);
}
 
namespace blender::io::usd {
 
USDArmatureWriter::USDArmatureWriter(const USDExporterContext &ctx) : USDAbstractWriter(ctx) {}
 
void USDArmatureWriter::do_write(HierarchyContext &context)
{
  if (!(context.object && context.object->type == OB_ARMATURE && context.object->data)) {
    BLI_assert_unreachable();
    return;
  }
 
  /* Create the skeleton. */
  pxr::UsdStageRefPtr stage = usd_export_context_.stage;
  pxr::UsdSkelSkeleton skel = pxr::UsdSkelSkeleton::Define(stage, usd_export_context_.usd_path);
 
  if (!skel) {
    CLOG_WARN(&LOG,
              "Couldn't define UsdSkelSkeleton %s",
              usd_export_context_.usd_path.GetString().c_str());
    return;
  }
 
  pxr::UsdSkelAnimation skel_anim;
 
  if (usd_export_context_.export_params.export_animation) {
    /* Create the skeleton animation primitive as a child of the skeleton. */
    pxr::SdfPath anim_path = usd_export_context_.usd_path.AppendChild(usdtokens::Anim);
    skel_anim = pxr::UsdSkelAnimation::Define(stage, anim_path);
 
    if (!skel_anim) {
      CLOG_WARN(&LOG, "Couldn't define UsdSkelAnimation %s", anim_path.GetString().c_str());
      return;
    }
  }
 
  const bool allow_unicode = usd_export_context_.export_params.allow_unicode;
  Map<StringRef, const Bone *> *deform_map = usd_export_context_.export_params.only_deform_bones ?
                                                 &deform_map_ :
                                                 nullptr;
 
  if (!this->frame_has_been_written_) {
    init_deform_bones_map(context.object, deform_map);
    initialize(context.object, skel, skel_anim, deform_map, allow_unicode);
  }
 
  if (usd_export_context_.export_params.export_animation) {
    add_anim_sample(skel_anim, context.object, get_export_time_code(), deform_map);
  }
}
 
bool USDArmatureWriter::check_is_animated(const HierarchyContext &context) const
{
  const Object *obj = context.object;
 
  if (!(obj && obj->type == OB_ARMATURE)) {
    return false;
  }
 
  return obj->adt != nullptr;
}
 
}  // namespace blender::io::usd