bool
PxrUsdKatana_AreRelTargetsFromBaseMaterial(const UsdRelationship &rel)
{
    // Find the strongest opinion about the relationship targets.
    SdfRelationshipSpecHandle strongestRelSpec;
    SdfPropertySpecHandleVector propStack = rel.GetPropertyStack();
    for (const SdfPropertySpecHandle &prop: propStack) {
        if (SdfRelationshipSpecHandle relSpec =
            TfDynamic_cast<SdfRelationshipSpecHandle>(prop)) {
            if (relSpec->HasTargetPathList()) {
                strongestRelSpec = relSpec;
                break;
            }
        }
    }
    // Find which prim node introduced that opinion.
    if (strongestRelSpec) {
        for(const PcpNodeRef &node:
            rel.GetPrim().GetPrimIndex().GetNodeRange()) {
            if (node.GetPath() == strongestRelSpec->GetPath().GetPrimPath() &&
                node.GetLayerStack()->HasLayer(strongestRelSpec->GetLayer())) {
                return _NodeRepresentsLiveBaseMaterial(node);
            }
        }
    }
    return false;
}

void
UsdRiStatementsAPI::SetCoordinateSystem(const std::string &coordSysName)
{
    UsdAttribute attr = GetPrim().CreateAttribute(_tokens->coordsys, 
                                                  SdfValueTypeNames->String, 
                                                  /* custom = */ false);
    if (TF_VERIFY(attr)) {
        attr.Set(coordSysName);

        UsdPrim currPrim = GetPrim();
        while (currPrim && currPrim.GetPath() != SdfPath::AbsoluteRootPath()) {
            if (currPrim.IsModel() && !currPrim.IsGroup() &&
                currPrim.GetPath() != SdfPath::AbsoluteRootPath()) {
                UsdRelationship rel =
                    currPrim.CreateRelationship(_tokens->modelCoordsys,
                                                /* custom = */ false);
                if (TF_VERIFY(rel)) {
                    // Order should not matter, since these are a set,
                    // but historically we have appended these.
                    rel.AddTarget(GetPrim().GetPath());
                }
                break;
            }

            currPrim = currPrim.GetParent();
        }
    }
}

UsdRelationship
UsdPrim::CreateRelationship(const TfToken& name, bool custom) const
{
    UsdRelationship rel = GetRelationship(name);
    rel._Create(custom);
    return rel;
}

UsdVolVolume::FieldMap
UsdVolVolume::GetFieldPaths() const
{
    std::map<TfToken, SdfPath> fieldMap;
    const UsdPrim &prim = GetPrim();

    if (prim) {
        std::vector<UsdProperty> fieldProps =
            prim.GetPropertiesInNamespace(_tokens->fieldPrefix);
        for (const UsdProperty &fieldProp : fieldProps) {
            UsdRelationship fieldRel = fieldProp.As<UsdRelationship>();
            SdfPathVector targets;

            // All relationships starting with "field:" should point to
            // UsdVolFieldBase primitives.
            if (fieldRel && fieldRel.GetForwardedTargets(&targets)) {
                if (targets.size() == 1 && 
                    targets.front().IsPrimPath()) {
                    fieldMap.emplace(fieldRel.GetBaseName(), targets.front());
                }
            }
        }
    }

    return fieldMap;
}

static string
__repr__(const UsdRelationship &self)
{
    if (self) {
        return TfStringPrintf("%s.GetRelationship(%s)",
                              TfPyRepr(self.GetPrim()).c_str(),
                              TfPyRepr(self.GetName()).c_str());
    } else {
        return "invalid " + self.GetDescription();
    }
}

bool 
UsdGeomCollectionAPI::IsEmpty() const
{
    UsdRelationship targetsRel = _GetTargetsRel();
    if (targetsRel) {
        SdfPathVector targets;
        targetsRel.GetTargets(&targets);
        return targets.empty();
    }
    return true;
}

bool
UsdVolVolume::CreateFieldRelationship(const TfToken &name,
	const SdfPath &fieldPath) const
{
    if (!fieldPath.IsPrimPath() && !fieldPath.IsPrimPropertyPath()){
        return false;
    }
    UsdRelationship fieldRel =
	GetPrim().CreateRelationship(_MakeNamespaced(name), /*custom*/true);

    if (fieldRel) {
	return fieldRel.SetTargets({fieldPath});
    }

    return false;
}

static SdfPathVector
_GetForwardedTargets(const UsdRelationship &self,
                     bool forwardToObjectsInMasters)
{
    SdfPathVector result;
    self.GetForwardedTargets(&result, forwardToObjectsInMasters);
    return result;
}

PXR_NAMESPACE_OPEN_SCOPE


// TODO: We should centralize this logic in a UsdImaging ShaderAdapter.

/*static*/
UsdPrim
UsdImaging_MaterialStrategy::GetTargetedShader(UsdPrim const& materialPrim,
                                        UsdRelationship const& materialRel)
{
    SdfPathVector targets;
    if (!materialRel.GetForwardedTargets(&targets))
        return UsdPrim();

    if (targets.size() != 1) {
        // XXX: This should really be a validation error once USD gets that
        // feature.
        TF_WARN("We expect only one target on relationship %s of prim <%s>, "
                "but got %zu.",
                materialRel.GetName().GetText(),
                materialPrim.GetPath().GetText(),
                targets.size());
        return UsdPrim();
    }

    if (!targets[0].IsPrimPath()) {
        // XXX: This should really be a validation error once USD gets that
        // feature.
        TF_WARN("We expect the target of the relationship %s of prim <%s> "
                "to be a prim, instead it is <%s>.",
                materialRel.GetName().GetText(),
                materialPrim.GetPath().GetText(),
                targets[0].GetText());
        return UsdPrim();
    }

    return materialPrim.GetStage()->GetPrimAtPath(targets[0]);
}

//.........这里部分代码省略.........
        //
        bool isPruned = (!pruneMaskValues.empty() and
                         pruneMaskValues[i] == false);
        if (isPruned)
        {
            omitList.push_back(i);
        }

        const SdfPath &protoPath = protoPaths[index];

        // Compute the full (Katana) path to this prototype.
        //
        std::string fullProtoPath;
        std::map<SdfPath, std::string>::const_iterator pptkpIt =
                protoPathsToKatPaths.find(protoPath);
        if (pptkpIt != protoPathsToKatPaths.end())
        {
            fullProtoPath = pptkpIt->second;
        }
        else
        {
            _PathToPrimMap::const_iterator pcIt = primCache.find(protoPath);
            const UsdPrim &protoPrim = pcIt->second;
            if (!protoPrim) {
                continue;
            }

            // Determine where (what path) to start building the prototype prim
            // such that its material bindings will be preserved. This could be
            // the prototype path itself or an ancestor path.
            //
            SdfPathVector commonPrefixes;

            UsdRelationship materialBindingsRel =
                    UsdShadeMaterial::GetBindingRel(protoPrim);

            auto assetAPI = UsdModelAPI(protoPrim);
            std::string assetName;
            bool isReferencedModelPrim =
                    assetAPI.IsModel() and assetAPI.GetAssetName(&assetName);

            if (!materialBindingsRel or isReferencedModelPrim)
            {
                // The prim has no material bindings or is a referenced model
                // prim (meaning that materials are defined below it); start
                // building at the prototype path.
                //
                commonPrefixes.push_back(protoPath);
            }
            else
            {
                SdfPathVector materialPaths;
                materialBindingsRel.GetForwardedTargets(&materialPaths);
                for (auto materialPath : materialPaths)
                {
                    const SdfPath &commonPrefix =
                            protoPath.GetCommonPrefix(materialPath);
                    if (commonPrefix.GetString() == "/")
                    {
                        // XXX Unhandled case.
                        // The prototype prim and its material are not under the
                        // same parent; start building at the prototype path
                        // (although it is likely that bindings will be broken).
                        //
                        commonPrefixes.push_back(protoPath);
                    }

bool
PxrUsdTranslators_InstancerWriter::writeInstancerAttrs(
        const UsdTimeCode& usdTime,
        const UsdGeomPointInstancer& instancer)
{
    MStatus status = MS::kSuccess;
    MFnDagNode dagNode(GetDagPath(), &status);
    CHECK_MSTATUS_AND_RETURN(status, false);

    // Note: In this function, we don't read instances using the provided
    // MFnInstancer API. One reason is that it breaks up prototypes into their
    // constituent shapes, and there's no way to figure out which hierarchy
    // they came from. Another reason is that it only provides computed matrices
    // and not separate position, rotation, scale attrs.

    const SdfPath prototypesGroupPath =
            instancer.GetPrim().GetPath().AppendChild(_tokens->Prototypes);

    // At the default time, setup all the prototype instances.
    if (usdTime.IsDefault()) {
        const MPlug inputHierarchy = dagNode.findPlug("inputHierarchy", true,
                &status);
        CHECK_MSTATUS_AND_RETURN(status, false);

        // Note that the "Prototypes" prim needs to be a model group to ensure
        // contiguous model hierarchy.
        const UsdPrim prototypesGroupPrim = GetUsdStage()->DefinePrim(
                prototypesGroupPath);
        UsdModelAPI(prototypesGroupPrim).SetKind(KindTokens->group);
        _modelPaths.push_back(prototypesGroupPath);

        UsdRelationship prototypesRel = instancer.CreatePrototypesRel();

        const unsigned int numElements = inputHierarchy.numElements();
        for (unsigned int i = 0; i < numElements; ++i) {
            const MPlug plug = inputHierarchy[i];
            const MPlug source(UsdMayaUtil::GetConnected(plug));
            if (source.isNull()) {
                TF_WARN("Cannot read prototype: the source plug %s was null",
                        plug.name().asChar());
                return false;
            }

            MFnDagNode sourceNode(source.node(), &status);
            CHECK_MSTATUS_AND_RETURN(status, false);

            MDagPath prototypeDagPath;
            sourceNode.getPath(prototypeDagPath);

            // Prototype names are guaranteed unique by virtue of having a
            // unique numerical suffix _# indicating the prototype index.
            const TfToken prototypeName(
                    TfStringPrintf("%s_%d", sourceNode.name().asChar(), i));
            const SdfPath prototypeUsdPath = prototypesGroupPrim.GetPath()
                    .AppendChild(prototypeName);
            UsdPrim prototypePrim = GetUsdStage()->DefinePrim(
                    prototypeUsdPath);
            _modelPaths.push_back(prototypeUsdPath);

            // Try to be conservative and only create an intermediary xformOp
            // with the instancerTranslate if we can ensure that we don't need
            // to compensate for the translation on the prototype root.
            //
            // XXX: instancerTranslate does not behave well when added to a
            // reference that has an existing transform on the far side of the
            // reference. However, its behavior at least matches the
            // behavior in UsdMayaTranslatorModelAssembly. If we fix the
            // behavior there, we need to make sure that this is also
            // fixed to match.
            bool instancerTranslateAnimated = false;
            if (_NeedsExtraInstancerTranslate(
                    prototypeDagPath, &instancerTranslateAnimated)) {
                UsdGeomXformable xformable(prototypePrim);
                UsdGeomXformOp newOp = xformable.AddTranslateOp(
                        UsdGeomXformOp::PrecisionDouble,
                        _tokens->instancerTranslate);
                _instancerTranslateOps.push_back(
                        {prototypeDagPath, newOp, instancerTranslateAnimated});
            }

            // Two notes:
            // (1) We don't un-instance here, because it's OK for the prototype
            // to just be a reference to an instance master if the prototype
            // participates in Maya native instancing.
            // (2) The prototype root must be visible to match Maya's behavior,
            // which always vis'es the prototype root, even if it is marked
            // hidden.
            _writeJobCtx.CreatePrimWriterHierarchy(
                    prototypeDagPath,
                    prototypeUsdPath,
                    /*forceUninstance*/ false,
                    /*exportRootVisibility*/ false,
                    &_prototypeWriters);
            prototypesRel.AddTarget(prototypeUsdPath);
        }

        _numPrototypes = numElements;
    }

    // If there aren't any prototypes, fail and don't export on subsequent
//.........这里部分代码省略.........

 void _Visit(UsdRelationship const &rel) {
     SdfPathVector targets;
     rel._GetForwardedTargets(&targets,
                              /*includeForwardingRels=*/true);
     _VisitImpl(targets);
 }

bool
UsdGeomPointInstancer::ComputeInstanceTransformsAtTime(
    VtArray<GfMatrix4d>* xforms,
    const UsdTimeCode time,
    const UsdTimeCode baseTime,
    const ProtoXformInclusion doProtoXforms,
    const MaskApplication applyMask) const
{
    // XXX: Need to add handling of velocities/angularVelocities and baseTime.
    (void)baseTime;

    if (!xforms) {
        TF_WARN("%s -- null container passed to ComputeInstanceTransformsAtTime()",
                GetPrim().GetPath().GetText());
        return false;
    }

    VtIntArray protoIndices;
    if (!GetProtoIndicesAttr().Get(&protoIndices, time)) {
        TF_WARN("%s -- no prototype indices",
                GetPrim().GetPath().GetText());
        return false;
    }

    if (protoIndices.empty()) {
        xforms->clear();
        return true;
    }

    VtVec3fArray positions;
    if (!GetPositionsAttr().Get(&positions, time)) {
        TF_WARN("%s -- no positions",
                GetPrim().GetPath().GetText());
        return false;
    }

    if (positions.size() != protoIndices.size()) {
        TF_WARN("%s -- positions.size() [%zu] != protoIndices.size() [%zu]",
                GetPrim().GetPath().GetText(),
                positions.size(),
                protoIndices.size());
        return false;
    }

    VtVec3fArray scales;
    GetScalesAttr().Get(&scales, time);
    if (!scales.empty() && scales.size() != protoIndices.size()) {
        TF_WARN("%s -- scales.size() [%zu] != protoIndices.size() [%zu]",
                GetPrim().GetPath().GetText(),
                scales.size(),
                protoIndices.size());
        return false;
    }

    VtQuathArray orientations;
    GetOrientationsAttr().Get(&orientations, time);
    if (!orientations.empty() && orientations.size() != protoIndices.size()) {
        TF_WARN("%s -- orientations.size() [%zu] != protoIndices.size() [%zu]",
                GetPrim().GetPath().GetText(),
                orientations.size(),
                protoIndices.size());
        return false;
    }

    // If we're going to include the prototype transforms, verify that we have
    // prototypes and that all of the protoIndices are in bounds.
    SdfPathVector protoPaths;
    if (doProtoXforms == IncludeProtoXform) {
        const UsdRelationship prototypes = GetPrototypesRel();
        if (!prototypes.GetTargets(&protoPaths) || protoPaths.empty()) {
            TF_WARN("%s -- no prototypes",
                    GetPrim().GetPath().GetText());
            return false;
        }

        TF_FOR_ALL(iter, protoIndices) {
            const int protoIndex = *iter;
            if (protoIndex < 0 || static_cast<size_t>(protoIndex) >= protoPaths.size()) {
                TF_WARN("%s -- invalid prototype index: %d. Should be in [0, %zu)",
                        GetPrim().GetPath().GetText(),
                        protoIndex,
                        protoPaths.size());
                return false;
            }
        }
    }

    // Compute the mask only if applyMask says we should, otherwise we leave
    // mask empty so that its application below is a no-op.
    std::vector<bool> mask;
    if (applyMask == ApplyMask) {
        mask = ComputeMaskAtTime(time);
        if (!mask.empty() && mask.size() != protoIndices.size()) {
            TF_WARN("%s -- mask.size() [%zu] != protoIndices.size() [%zu]",
                    GetPrim().GetPath().GetText(),
                    mask.size(),
                    protoIndices.size());
            return false;
        }
    }
//.........这里部分代码省略.........

static FnKat::Attribute
_GetMaterialAssignAttr(
        const UsdPrim& prim,
        const PxrUsdKatanaUsdInPrivateData& data)
{
    if (not prim or prim.GetPath() == SdfPath::AbsoluteRootPath()) {
        // Special-case to pre-empt coding errors.
        return FnKat::Attribute();
    }

    UsdRelationship usdRel = UsdShadeLook::GetBindingRel(prim);
    if (usdRel) {
        // USD shading binding
        SdfPathVector targetPaths;
        usdRel.GetForwardedTargets(&targetPaths);
        if (targetPaths.size() > 0) {
            if (not targetPaths[0].IsPrimPath()) {
                FnLogWarn("Target path " << prim.GetPath().GetString() <<
                          " is not a prim");
                return FnKat::Attribute();
            }

            // This is a copy as it could be modified below.
            SdfPath targetPath = targetPaths[0];
            UsdPrim targetPrim = data.GetUsdInArgs()->GetStage()->GetPrimAtPath(targetPath);
            // If the target is inside a master, then it needs to be re-targeted 
            // to the instance.
            // 
            // XXX remove this special awareness once GetMasterWithContext is
            //     is available as the provided prim will automatically
            //     retarget (or provide enough context to retarget without
            //     tracking manually).
            if (targetPrim and targetPrim.IsInMaster()) {
                if (not data.GetInstancePath().IsEmpty() and 
                        not data.GetMasterPath().IsEmpty()) {

                    // Check if the source and the target of the relationship 
                    // belong to the same master.
                    // If they do, we have the context necessary to do the 
                    // re-mapping.
                    if (data.GetMasterPath().GetCommonPrefix(targetPath).
                            GetPathElementCount() > 0) {
                        targetPath = data.GetInstancePath().AppendPath(
                            targetPath.ReplacePrefix(targetPath.GetPrefixes()[0],
                                SdfPath::ReflexiveRelativePath()));
                    } else {
                        // Warn saying the target of relationship isn't within 
                        // the same master as the source.
                        FnLogWarn("Target path " << prim.GetPath().GetString() 
                            << " isn't within the master " << data.GetMasterPath());
                        return FnKat::Attribute();
                    }
                } else {
                    // XXX
                    // When loading beneath a master via an isolatePath
                    // opArg, we can encounter targets which are within masters
                    // but not within the context of a material.
                    // While that would be an error according to the below
                    // warning, it produces the expected results.
                    // This case can occur when expanding pointinstancers as
                    // the sources are made via execution of PxrUsdIn again
                    // at the sub-trees.
                    
                    
                    // Warn saying target of relationship is in a master, 
                    // but the associated instance path is unknown!
                    // FnLogWarn("Target path " << prim.GetPath().GetString() 
                    //         << " is within a master, but the associated "
                    //         "instancePath is unknown.");
                    // return FnKat::Attribute();
                }
            }

            // Convert the target path to the equivalent katana location.
            // XXX: Looks may have an atypical USD->Katana 
            // path mapping
            std::string location =
                PxrUsdKatanaUtils::ConvertUsdLookPathToKatLocation(targetPath, data);
                
            // XXX Looks containing only display terminals are causing issues
            //     with katana material manipulation workflows.
            //     For now: exclude any material assign which doesn't include
            //     /Looks/ in the path
            if (location.find(UsdKatanaTokens->katanaLooksScopePathSubstring)
                    == std::string::npos)
            {
                return FnKat::Attribute();
            }
                
                
            // location = TfStringReplace(location, "/Looks/", "/Materials/");
            // XXX handle multiple assignments
            return FnKat::StringAttribute(location);
        }
    }

    return FnKat::Attribute();
}