test2/source/blender/blenkernel/intern/attribute_access.cc

/*
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

#include <utility>

#include "BKE_attribute_access.hh"
#include "BKE_attribute_math.hh"
#include "BKE_customdata.h"
#include "BKE_deform.h"
#include "BKE_geometry_set.hh"
#include "BKE_mesh.h"
#include "BKE_pointcloud.h"

#include "DNA_mesh_types.h"
#include "DNA_meshdata_types.h"
#include "DNA_pointcloud_types.h"

#include "BLI_color.hh"
#include "BLI_float2.hh"
#include "BLI_span.hh"

#include "CLG_log.h"

#include "NOD_type_conversions.hh"

#include "attribute_access_intern.hh"

static CLG_LogRef LOG = {"bke.attribute_access"};

using blender::float3;
using blender::Set;
using blender::StringRef;
using blender::StringRefNull;
using blender::fn::GMutableSpan;

namespace blender::bke {

const blender::fn::CPPType *custom_data_type_to_cpp_type(const CustomDataType type)
{
  switch (type) {
    case CD_PROP_FLOAT:
      return &CPPType::get<float>();
    case CD_PROP_FLOAT2:
      return &CPPType::get<float2>();
    case CD_PROP_FLOAT3:
      return &CPPType::get<float3>();
    case CD_PROP_INT32:
      return &CPPType::get<int>();
    case CD_PROP_COLOR:
      return &CPPType::get<Color4f>();
    case CD_PROP_BOOL:
      return &CPPType::get<bool>();
    default:
      return nullptr;
  }
  return nullptr;
}

CustomDataType cpp_type_to_custom_data_type(const blender::fn::CPPType &type)
{
  if (type.is<float>()) {
    return CD_PROP_FLOAT;
  }
  if (type.is<float2>()) {
    return CD_PROP_FLOAT2;
  }
  if (type.is<float3>()) {
    return CD_PROP_FLOAT3;
  }
  if (type.is<int>()) {
    return CD_PROP_INT32;
  }
  if (type.is<Color4f>()) {
    return CD_PROP_COLOR;
  }
  if (type.is<bool>()) {
    return CD_PROP_BOOL;
  }
  return static_cast<CustomDataType>(-1);
}

static int attribute_data_type_complexity(const CustomDataType data_type)
{
  switch (data_type) {
    case CD_PROP_BOOL:
      return 0;
    case CD_PROP_INT32:
      return 1;
    case CD_PROP_FLOAT:
      return 2;
    case CD_PROP_FLOAT2:
      return 3;
    case CD_PROP_FLOAT3:
      return 4;
    case CD_PROP_COLOR:
      return 5;
#if 0 /* These attribute types are not supported yet. */
    case CD_MLOOPCOL:
      return 3;
    case CD_PROP_STRING:
      return 6;
#endif
    default:
      /* Only accept "generic" custom data types used by the attribute system. */
      BLI_assert_unreachable();
      return 0;
  }
}

CustomDataType attribute_data_type_highest_complexity(Span<CustomDataType> data_types)
{
  int highest_complexity = INT_MIN;
  CustomDataType most_complex_type = CD_PROP_COLOR;

  for (const CustomDataType data_type : data_types) {
    const int complexity = attribute_data_type_complexity(data_type);
    if (complexity > highest_complexity) {
      highest_complexity = complexity;
      most_complex_type = data_type;
    }
  }

  return most_complex_type;
}

/**
 * \note Generally the order should mirror the order of the domains
 * established in each component's ComponentAttributeProviders.
 */
static int attribute_domain_priority(const AttributeDomain domain)
{
  switch (domain) {
#if 0
    case ATTR_DOMAIN_CURVE:
      return 0;
#endif
    case ATTR_DOMAIN_FACE:
      return 1;
    case ATTR_DOMAIN_EDGE:
      return 2;
    case ATTR_DOMAIN_POINT:
      return 3;
    case ATTR_DOMAIN_CORNER:
      return 4;
    default:
      /* Domain not supported in nodes yet. */
      BLI_assert_unreachable();
      return 0;
  }
}

/**
 * Domains with a higher "information density" have a higher priority, in order
 * to choose a domain that will not lose data through domain conversion.
 */
AttributeDomain attribute_domain_highest_priority(Span<AttributeDomain> domains)
{
  int highest_priority = INT_MIN;
  AttributeDomain highest_priority_domain = ATTR_DOMAIN_CORNER;

  for (const AttributeDomain domain : domains) {
    const int priority = attribute_domain_priority(domain);
    if (priority > highest_priority) {
      highest_priority = priority;
      highest_priority_domain = domain;
    }
  }

  return highest_priority_domain;
}

void OutputAttribute::save()
{
  if (optional_span_varray_.has_value()) {
    optional_span_varray_->save();
  }
  if (save_) {
    save_(*this);
  }
}

GVArrayPtr BuiltinCustomDataLayerProvider::try_get_for_read(
    const GeometryComponent &component) const
{
  const CustomData *custom_data = custom_data_access_.get_const_custom_data(component);
  if (custom_data == nullptr) {
    return {};
  }

  const int domain_size = component.attribute_domain_size(domain_);
  const void *data = CustomData_get_layer(custom_data, stored_type_);
  if (data == nullptr) {
    return {};
  }
  return as_read_attribute_(data, domain_size);
}

GVMutableArrayPtr BuiltinCustomDataLayerProvider::try_get_for_write(
    GeometryComponent &component) const
{
  if (writable_ != Writable) {
    return {};
  }
  CustomData *custom_data = custom_data_access_.get_custom_data(component);
  if (custom_data == nullptr) {
    return {};
  }
  const int domain_size = component.attribute_domain_size(domain_);
  void *data = CustomData_get_layer(custom_data, stored_type_);
  if (data == nullptr) {
    return {};
  }
  void *new_data = CustomData_duplicate_referenced_layer(custom_data, stored_type_, domain_size);
  if (data != new_data) {
    custom_data_access_.update_custom_data_pointers(component);
    data = new_data;
  }
  if (update_on_write_ != nullptr) {
    update_on_write_(component);
  }
  return as_write_attribute_(data, domain_size);
}

bool BuiltinCustomDataLayerProvider::try_delete(GeometryComponent &component) const
{
  if (deletable_ != Deletable) {
    return false;
  }
  CustomData *custom_data = custom_data_access_.get_custom_data(component);
  if (custom_data == nullptr) {
    return {};
  }

  const int domain_size = component.attribute_domain_size(domain_);
  const int layer_index = CustomData_get_layer_index(custom_data, stored_type_);
  const bool delete_success = CustomData_free_layer(
      custom_data, stored_type_, domain_size, layer_index);
  if (delete_success) {
    custom_data_access_.update_custom_data_pointers(component);
  }
  return delete_success;
}

bool BuiltinCustomDataLayerProvider::try_create(GeometryComponent &component) const
{
  if (createable_ != Creatable) {
    return false;
  }
  CustomData *custom_data = custom_data_access_.get_custom_data(component);
  if (custom_data == nullptr) {
    return false;
  }
  if (CustomData_get_layer(custom_data, stored_type_) != nullptr) {
    /* Exists already. */
    return false;
  }
  const int domain_size = component.attribute_domain_size(domain_);
  const void *data = CustomData_add_layer(
      custom_data, stored_type_, CD_DEFAULT, nullptr, domain_size);
  const bool success = data != nullptr;
  if (success) {
    custom_data_access_.update_custom_data_pointers(component);
  }
  return success;
}

bool BuiltinCustomDataLayerProvider::exists(const GeometryComponent &component) const
{
  const CustomData *custom_data = custom_data_access_.get_const_custom_data(component);
  if (custom_data == nullptr) {
    return false;
  }
  const void *data = CustomData_get_layer(custom_data, stored_type_);
  return data != nullptr;
}

ReadAttributeLookup CustomDataAttributeProvider::try_get_for_read(
    const GeometryComponent &component, const StringRef attribute_name) const
{
  const CustomData *custom_data = custom_data_access_.get_const_custom_data(component);
  if (custom_data == nullptr) {
    return {};
  }
  const int domain_size = component.attribute_domain_size(domain_);
  for (const CustomDataLayer &layer : Span(custom_data->layers, custom_data->totlayer)) {
    if (layer.name != attribute_name) {
      continue;
    }
    const CustomDataType data_type = (CustomDataType)layer.type;
    switch (data_type) {
      case CD_PROP_FLOAT:
        return this->layer_to_read_attribute<float>(layer, domain_size);
      case CD_PROP_FLOAT2:
        return this->layer_to_read_attribute<float2>(layer, domain_size);
      case CD_PROP_FLOAT3:
        return this->layer_to_read_attribute<float3>(layer, domain_size);
      case CD_PROP_INT32:
        return this->layer_to_read_attribute<int>(layer, domain_size);
      case CD_PROP_COLOR:
        return this->layer_to_read_attribute<Color4f>(layer, domain_size);
      case CD_PROP_BOOL:
        return this->layer_to_read_attribute<bool>(layer, domain_size);
      default:
        break;
    }
  }
  return {};
}

WriteAttributeLookup CustomDataAttributeProvider::try_get_for_write(
    GeometryComponent &component, const StringRef attribute_name) const
{
  CustomData *custom_data = custom_data_access_.get_custom_data(component);
  if (custom_data == nullptr) {
    return {};
  }
  const int domain_size = component.attribute_domain_size(domain_);
  for (CustomDataLayer &layer : MutableSpan(custom_data->layers, custom_data->totlayer)) {
    if (layer.name != attribute_name) {
      continue;
    }
    CustomData_duplicate_referenced_layer_named(custom_data, layer.type, layer.name, domain_size);
    const CustomDataType data_type = (CustomDataType)layer.type;
    switch (data_type) {
      case CD_PROP_FLOAT:
        return this->layer_to_write_attribute<float>(layer, domain_size);
      case CD_PROP_FLOAT2:
        return this->layer_to_write_attribute<float2>(layer, domain_size);
      case CD_PROP_FLOAT3:
        return this->layer_to_write_attribute<float3>(layer, domain_size);
      case CD_PROP_INT32:
        return this->layer_to_write_attribute<int>(layer, domain_size);
      case CD_PROP_COLOR:
        return this->layer_to_write_attribute<Color4f>(layer, domain_size);
      case CD_PROP_BOOL:
        return this->layer_to_write_attribute<bool>(layer, domain_size);
      default:
        break;
    }
  }
  return {};
}

bool CustomDataAttributeProvider::try_delete(GeometryComponent &component,
                                             const StringRef attribute_name) const
{
  CustomData *custom_data = custom_data_access_.get_custom_data(component);
  if (custom_data == nullptr) {
    return false;
  }
  const int domain_size = component.attribute_domain_size(domain_);
  for (const int i : IndexRange(custom_data->totlayer)) {
    const CustomDataLayer &layer = custom_data->layers[i];
    if (this->type_is_supported((CustomDataType)layer.type) && layer.name == attribute_name) {
      CustomData_free_layer(custom_data, layer.type, domain_size, i);
      return true;
    }
  }
  return false;
}

bool CustomDataAttributeProvider::try_create(GeometryComponent &component,
                                             const StringRef attribute_name,
                                             const AttributeDomain domain,
                                             const CustomDataType data_type) const
{
  if (domain_ != domain) {
    return false;
  }
  if (!this->type_is_supported(data_type)) {
    return false;
  }
  CustomData *custom_data = custom_data_access_.get_custom_data(component);
  if (custom_data == nullptr) {
    return false;
  }
  for (const CustomDataLayer &layer : Span(custom_data->layers, custom_data->totlayer)) {
    if (layer.name == attribute_name) {
      return false;
    }
  }
  const int domain_size = component.attribute_domain_size(domain_);
  char attribute_name_c[MAX_NAME];
  attribute_name.copy(attribute_name_c);
  CustomData_add_layer_named(
      custom_data, data_type, CD_DEFAULT, nullptr, domain_size, attribute_name_c);
  return true;
}

bool CustomDataAttributeProvider::foreach_attribute(const GeometryComponent &component,
                                                    const AttributeForeachCallback callback) const
{
  const CustomData *custom_data = custom_data_access_.get_const_custom_data(component);
  if (custom_data == nullptr) {
    return true;
  }
  for (const CustomDataLayer &layer : Span(custom_data->layers, custom_data->totlayer)) {
    const CustomDataType data_type = (CustomDataType)layer.type;
    if (this->type_is_supported(data_type)) {
      AttributeMetaData meta_data{domain_, data_type};
      if (!callback(layer.name, meta_data)) {
        return false;
      }
    }
  }
  return true;
}

ReadAttributeLookup NamedLegacyCustomDataProvider::try_get_for_read(
    const GeometryComponent &component, const StringRef attribute_name) const
{
  const CustomData *custom_data = custom_data_access_.get_const_custom_data(component);
  if (custom_data == nullptr) {
    return {};
  }
  for (const CustomDataLayer &layer : Span(custom_data->layers, custom_data->totlayer)) {
    if (layer.type == stored_type_) {
      if (layer.name == attribute_name) {
        const int domain_size = component.attribute_domain_size(domain_);
        return {as_read_attribute_(layer.data, domain_size), domain_};
      }
    }
  }
  return {};
}

WriteAttributeLookup NamedLegacyCustomDataProvider::try_get_for_write(
    GeometryComponent &component, const StringRef attribute_name) const
{
  CustomData *custom_data = custom_data_access_.get_custom_data(component);
  if (custom_data == nullptr) {
    return {};
  }
  for (CustomDataLayer &layer : MutableSpan(custom_data->layers, custom_data->totlayer)) {
    if (layer.type == stored_type_) {
      if (layer.name == attribute_name) {
        const int domain_size = component.attribute_domain_size(domain_);
        void *data_old = layer.data;
        void *data_new = CustomData_duplicate_referenced_layer_named(
            custom_data, stored_type_, layer.name, domain_size);
        if (data_old != data_new) {
          custom_data_access_.update_custom_data_pointers(component);
        }
        return {as_write_attribute_(layer.data, domain_size), domain_};
      }
    }
  }
  return {};
}

bool NamedLegacyCustomDataProvider::try_delete(GeometryComponent &component,
                                               const StringRef attribute_name) const
{
  CustomData *custom_data = custom_data_access_.get_custom_data(component);
  if (custom_data == nullptr) {
    return false;
  }
  for (const int i : IndexRange(custom_data->totlayer)) {
    const CustomDataLayer &layer = custom_data->layers[i];
    if (layer.type == stored_type_) {
      if (layer.name == attribute_name) {
        const int domain_size = component.attribute_domain_size(domain_);
        CustomData_free_layer(custom_data, stored_type_, domain_size, i);
        custom_data_access_.update_custom_data_pointers(component);
        return true;
      }
    }
  }
  return false;
}

bool NamedLegacyCustomDataProvider::foreach_attribute(
    const GeometryComponent &component, const AttributeForeachCallback callback) const
{
  const CustomData *custom_data = custom_data_access_.get_const_custom_data(component);
  if (custom_data == nullptr) {
    return true;
  }
  for (const CustomDataLayer &layer : Span(custom_data->layers, custom_data->totlayer)) {
    if (layer.type == stored_type_) {
      AttributeMetaData meta_data{domain_, attribute_type_};
      if (!callback(layer.name, meta_data)) {
        return false;
      }
    }
  }
  return true;
}

void NamedLegacyCustomDataProvider::foreach_domain(
    const FunctionRef<void(AttributeDomain)> callback) const
{
  callback(domain_);
}

}  // namespace blender::bke

/* -------------------------------------------------------------------- */
/** \name Geometry Component
 * \{ */

const blender::bke::ComponentAttributeProviders *GeometryComponent::get_attribute_providers() const
{
  return nullptr;
}

bool GeometryComponent::attribute_domain_supported(const AttributeDomain domain) const
{
  using namespace blender::bke;
  const ComponentAttributeProviders *providers = this->get_attribute_providers();
  if (providers == nullptr) {
    return false;
  }
  return providers->supported_domains().contains(domain);
}

int GeometryComponent::attribute_domain_size(const AttributeDomain UNUSED(domain)) const
{
  return 0;
}

bool GeometryComponent::attribute_is_builtin(const blender::StringRef attribute_name) const
{
  using namespace blender::bke;
  const ComponentAttributeProviders *providers = this->get_attribute_providers();
  if (providers == nullptr) {
    return false;
  }
  return providers->builtin_attribute_providers().contains_as(attribute_name);
}

blender::bke::ReadAttributeLookup GeometryComponent::attribute_try_get_for_read(
    const StringRef attribute_name) const
{
  using namespace blender::bke;
  const ComponentAttributeProviders *providers = this->get_attribute_providers();
  if (providers == nullptr) {
    return {};
  }
  const BuiltinAttributeProvider *builtin_provider =
      providers->builtin_attribute_providers().lookup_default_as(attribute_name, nullptr);
  if (builtin_provider != nullptr) {
    return {builtin_provider->try_get_for_read(*this), builtin_provider->domain()};
  }
  for (const DynamicAttributesProvider *dynamic_provider :
       providers->dynamic_attribute_providers()) {
    ReadAttributeLookup attribute = dynamic_provider->try_get_for_read(*this, attribute_name);
    if (attribute) {
      return attribute;
    }
  }
  return {};
}

std::unique_ptr<blender::fn::GVArray> GeometryComponent::attribute_try_adapt_domain(
    std::unique_ptr<blender::fn::GVArray> varray,
    const AttributeDomain from_domain,
    const AttributeDomain to_domain) const
{
  if (from_domain == to_domain) {
    return varray;
  }
  return {};
}

blender::bke::WriteAttributeLookup GeometryComponent::attribute_try_get_for_write(
    const StringRef attribute_name)
{
  using namespace blender::bke;
  const ComponentAttributeProviders *providers = this->get_attribute_providers();
  if (providers == nullptr) {
    return {};
  }
  const BuiltinAttributeProvider *builtin_provider =
      providers->builtin_attribute_providers().lookup_default_as(attribute_name, nullptr);
  if (builtin_provider != nullptr) {
    return {builtin_provider->try_get_for_write(*this), builtin_provider->domain()};
  }
  for (const DynamicAttributesProvider *dynamic_provider :
       providers->dynamic_attribute_providers()) {
    WriteAttributeLookup attribute = dynamic_provider->try_get_for_write(*this, attribute_name);
    if (attribute) {
      return attribute;
    }
  }
  return {};
}

bool GeometryComponent::attribute_try_delete(const StringRef attribute_name)
{
  using namespace blender::bke;
  const ComponentAttributeProviders *providers = this->get_attribute_providers();
  if (providers == nullptr) {
    return {};
  }
  const BuiltinAttributeProvider *builtin_provider =
      providers->builtin_attribute_providers().lookup_default_as(attribute_name, nullptr);
  if (builtin_provider != nullptr) {
    return builtin_provider->try_delete(*this);
  }
  bool success = false;
  for (const DynamicAttributesProvider *dynamic_provider :
       providers->dynamic_attribute_providers()) {
    success = dynamic_provider->try_delete(*this, attribute_name) || success;
  }
  return success;
}

bool GeometryComponent::attribute_try_create(const StringRef attribute_name,
                                             const AttributeDomain domain,
                                             const CustomDataType data_type)
{
  using namespace blender::bke;
  if (attribute_name.is_empty()) {
    return false;
  }
  const ComponentAttributeProviders *providers = this->get_attribute_providers();
  if (providers == nullptr) {
    return false;
  }
  const BuiltinAttributeProvider *builtin_provider =
      providers->builtin_attribute_providers().lookup_default_as(attribute_name, nullptr);
  if (builtin_provider != nullptr) {
    if (builtin_provider->domain() != domain) {
      return false;
    }
    if (builtin_provider->data_type() != data_type) {
      return false;
    }
    return builtin_provider->try_create(*this);
  }
  for (const DynamicAttributesProvider *dynamic_provider :
       providers->dynamic_attribute_providers()) {
    if (dynamic_provider->try_create(*this, attribute_name, domain, data_type)) {
      return true;
    }
  }
  return false;
}

bool GeometryComponent::attribute_try_create_builtin(const blender::StringRef attribute_name)
{
  using namespace blender::bke;
  if (attribute_name.is_empty()) {
    return false;
  }
  const ComponentAttributeProviders *providers = this->get_attribute_providers();
  if (providers == nullptr) {
    return false;
  }
  const BuiltinAttributeProvider *builtin_provider =
      providers->builtin_attribute_providers().lookup_default_as(attribute_name, nullptr);
  if (builtin_provider == nullptr) {
    return false;
  }
  return builtin_provider->try_create(*this);
}

Set<std::string> GeometryComponent::attribute_names() const
{
  Set<std::string> attributes;
  this->attribute_foreach([&](StringRefNull name, const AttributeMetaData &UNUSED(meta_data)) {
    attributes.add(name);
    return true;
  });
  return attributes;
}

/**
 * \return False if the callback explicitly returned false at any point, otherwise true,
 * meaning the callback made it all the way through.
 */
bool GeometryComponent::attribute_foreach(const AttributeForeachCallback callback) const
{
  using namespace blender::bke;
  const ComponentAttributeProviders *providers = this->get_attribute_providers();
  if (providers == nullptr) {
    return true;
  }

  /* Keep track handled attribute names to make sure that we do not return the same name twice. */
  Set<std::string> handled_attribute_names;

  for (const BuiltinAttributeProvider *provider :
       providers->builtin_attribute_providers().values()) {
    if (provider->exists(*this)) {
      AttributeMetaData meta_data{provider->domain(), provider->data_type()};
      if (!callback(provider->name(), meta_data)) {
        return false;
      }
      handled_attribute_names.add_new(provider->name());
    }
  }
  for (const DynamicAttributesProvider *provider : providers->dynamic_attribute_providers()) {
    const bool continue_loop = provider->foreach_attribute(
        *this, [&](StringRefNull name, const AttributeMetaData &meta_data) {
          if (handled_attribute_names.add(name)) {
            return callback(name, meta_data);
          }
          return true;
        });
    if (!continue_loop) {
      return false;
    }
  }

  return true;
}

bool GeometryComponent::attribute_exists(const blender::StringRef attribute_name) const
{
  blender::bke::ReadAttributeLookup attribute = this->attribute_try_get_for_read(attribute_name);
  if (attribute) {
    return true;
  }
  return false;
}

static std::unique_ptr<blender::fn::GVArray> try_adapt_data_type(
    std::unique_ptr<blender::fn::GVArray> varray, const blender::fn::CPPType &to_type)
{
  const blender::nodes::DataTypeConversions &conversions =
      blender::nodes::get_implicit_type_conversions();
  return conversions.try_convert(std::move(varray), to_type);
}

std::unique_ptr<blender::fn::GVArray> GeometryComponent::attribute_try_get_for_read(
    const StringRef attribute_name,
    const AttributeDomain domain,
    const CustomDataType data_type) const
{
  blender::bke::ReadAttributeLookup attribute = this->attribute_try_get_for_read(attribute_name);
  if (!attribute) {
    return {};
  }

  std::unique_ptr<blender::fn::GVArray> varray = std::move(attribute.varray);
  if (domain != ATTR_DOMAIN_AUTO && attribute.domain != domain) {
    varray = this->attribute_try_adapt_domain(std::move(varray), attribute.domain, domain);
    if (!varray) {
      return {};
    }
  }

  const blender::fn::CPPType *cpp_type = blender::bke::custom_data_type_to_cpp_type(data_type);
  BLI_assert(cpp_type != nullptr);
  if (varray->type() != *cpp_type) {
    varray = try_adapt_data_type(std::move(varray), *cpp_type);
    if (!varray) {
      return {};
    }
  }

  return varray;
}

std::unique_ptr<blender::bke::GVArray> GeometryComponent::attribute_try_get_for_read(
    const StringRef attribute_name, const AttributeDomain domain) const
{
  if (!this->attribute_domain_supported(domain)) {
    return {};
  }

  blender::bke::ReadAttributeLookup attribute = this->attribute_try_get_for_read(attribute_name);
  if (!attribute) {
    return {};
  }

  if (attribute.domain != domain) {
    return this->attribute_try_adapt_domain(std::move(attribute.varray), attribute.domain, domain);
  }

  return std::move(attribute.varray);
}

std::unique_ptr<blender::bke::GVArray> GeometryComponent::attribute_get_for_read(
    const StringRef attribute_name,
    const AttributeDomain domain,
    const CustomDataType data_type,
    const void *default_value) const
{
  std::unique_ptr<blender::bke::GVArray> varray = this->attribute_try_get_for_read(
      attribute_name, domain, data_type);
  if (varray) {
    return varray;
  }
  const blender::fn::CPPType *type = blender::bke::custom_data_type_to_cpp_type(data_type);
  if (default_value == nullptr) {
    default_value = type->default_value();
  }
  const int domain_size = this->attribute_domain_size(domain);
  return std::make_unique<blender::fn::GVArray_For_SingleValue>(*type, domain_size, default_value);
}

class GVMutableAttribute_For_OutputAttribute
    : public blender::fn::GVMutableArray_For_GMutableSpan {
 public:
  GeometryComponent *component;
  std::string final_name;

  GVMutableAttribute_For_OutputAttribute(GMutableSpan data,
                                         GeometryComponent &component,
                                         std::string final_name)
      : blender::fn::GVMutableArray_For_GMutableSpan(data),
        component(&component),
        final_name(std::move(final_name))
  {
  }

  ~GVMutableAttribute_For_OutputAttribute() override
  {
    type_->destruct_n(data_, size_);
    MEM_freeN(data_);
  }
};

static void save_output_attribute(blender::bke::OutputAttribute &output_attribute)
{
  using namespace blender;
  using namespace blender::fn;
  using namespace blender::bke;

  GVMutableAttribute_For_OutputAttribute &varray =
      dynamic_cast<GVMutableAttribute_For_OutputAttribute &>(output_attribute.varray());

  GeometryComponent &component = *varray.component;
  const StringRefNull name = varray.final_name;
  const AttributeDomain domain = output_attribute.domain();
  const CustomDataType data_type = output_attribute.custom_data_type();
  const CPPType &cpp_type = output_attribute.cpp_type();

  component.attribute_try_delete(name);
  if (!component.attribute_try_create(varray.final_name, domain, data_type)) {
    CLOG_WARN(&LOG,
              "Could not create the '%s' attribute with type '%s'.",
              name.c_str(),
              cpp_type.name().c_str());
    return;
  }
  WriteAttributeLookup write_attribute = component.attribute_try_get_for_write(name);
  BUFFER_FOR_CPP_TYPE_VALUE(varray.type(), buffer);
  for (const int i : IndexRange(varray.size())) {
    varray.get(i, buffer);
    write_attribute.varray->set_by_relocate(i, buffer);
  }
}

static blender::bke::OutputAttribute create_output_attribute(
    GeometryComponent &component,
    const blender::StringRef attribute_name,
    const AttributeDomain domain,
    const CustomDataType data_type,
    const bool ignore_old_values,
    const void *default_value)
{
  using namespace blender;
  using namespace blender::fn;
  using namespace blender::bke;

  if (attribute_name.is_empty()) {
    return {};
  }

  const CPPType *cpp_type = custom_data_type_to_cpp_type(data_type);
  BLI_assert(cpp_type != nullptr);
  const nodes::DataTypeConversions &conversions = nodes::get_implicit_type_conversions();

  if (component.attribute_is_builtin(attribute_name)) {
    WriteAttributeLookup attribute = component.attribute_try_get_for_write(attribute_name);
    if (!attribute) {
      component.attribute_try_create_builtin(attribute_name);
      attribute = component.attribute_try_get_for_write(attribute_name);
      if (!attribute) {
        /* Builtin attribute does not exist and can't be created. */
        return {};
      }
    }
    if (attribute.domain != domain) {
      /* Builtin attribute is on different domain. */
      return {};
    }
    GVMutableArrayPtr varray = std::move(attribute.varray);
    if (varray->type() == *cpp_type) {
      /* Builtin attribute matches exactly. */
      return OutputAttribute(std::move(varray), domain, {}, ignore_old_values);
    }
    /* Builtin attribute is on the same domain but has a different data type. */
    varray = conversions.try_convert(std::move(varray), *cpp_type);
    return OutputAttribute(std::move(varray), domain, {}, ignore_old_values);
  }

  WriteAttributeLookup attribute = component.attribute_try_get_for_write(attribute_name);
  if (!attribute) {
    component.attribute_try_create(attribute_name, domain, data_type);
    attribute = component.attribute_try_get_for_write(attribute_name);
    if (!attribute) {
      /* Can't create the attribute. */
      return {};
    }
  }
  if (attribute.domain == domain && attribute.varray->type() == *cpp_type) {
    /* Existing generic attribute matches exactly. */
    return OutputAttribute(std::move(attribute.varray), domain, {}, ignore_old_values);
  }

  const int domain_size = component.attribute_domain_size(domain);
  /* Allocate a new array that lives next to the existing attribute. It will overwrite the existing
   * attribute after processing is done. */
  void *data = MEM_mallocN_aligned(
      cpp_type->size() * domain_size, cpp_type->alignment(), __func__);
  if (ignore_old_values) {
    /* This does nothing for trivially constructible types, but is necessary for correctness. */
    cpp_type->construct_default_n(data, domain);
  }
  else {
    /* Fill the temporary array with values from the existing attribute. */
    GVArrayPtr old_varray = component.attribute_get_for_read(
        attribute_name, domain, data_type, default_value);
    old_varray->materialize_to_uninitialized(IndexRange(domain_size), data);
  }
  GVMutableArrayPtr varray = std::make_unique<GVMutableAttribute_For_OutputAttribute>(
      GMutableSpan{*cpp_type, data, domain_size}, component, attribute_name);

  return OutputAttribute(std::move(varray), domain, save_output_attribute, true);
}

blender::bke::OutputAttribute GeometryComponent::attribute_try_get_for_output(
    const StringRef attribute_name,
    const AttributeDomain domain,
    const CustomDataType data_type,
    const void *default_value)
{
  return create_output_attribute(*this, attribute_name, domain, data_type, false, default_value);
}

blender::bke::OutputAttribute GeometryComponent::attribute_try_get_for_output_only(
    const blender::StringRef attribute_name,
    const AttributeDomain domain,
    const CustomDataType data_type)
{
  return create_output_attribute(*this, attribute_name, domain, data_type, true, nullptr);
}