Class basic_snapshot
Synopsis
#include <src/entt/entity/snapshot.hpp>
template<typename Entity>
class basic_snapshot
Description
Utility class to create snapshots from a registry.
A snapshot can be either a dump of the entire registry or a narrower selection of components of interest.
This type can be used in both cases if provided with a correctly configured output archive.
- Template Parameters
Entity- A valid entity type (see entt_traits for more details).
Methods
| basic_snapshot overload | Constructs an instance that is bound to a given registry. | |
| basic_snapshot overload | Default move constructor. | |
| component overload | Puts aside the given components. | |
| component overload | Puts aside the given components for the entities in a range. | |
| entities | Puts aside all the entities from the underlying registry. | |
| operator= | Default move assignment operator. |
Source
Lines 31-148 in src/entt/entity/snapshot.hpp.
template<typename Entity>
class basic_snapshot {
using entity_traits = entt_traits<Entity>;
template<typename Component, typename Archive, typename It>
void get(Archive &archive, std::size_t sz, It first, It last) const {
const auto view = reg->template view<std::add_const_t<Component>>();
archive(typename entity_traits::entity_type(sz));
while(first != last) {
const auto entt = *(first++);
if(reg->template all_of<Component>(entt)) {
std::apply(archive, std::tuple_cat(std::make_tuple(entt), view.get(entt)));
}
}
}
template<typename... Component, typename Archive, typename It, std::size_t... Index>
void component(Archive &archive, It first, It last, std::index_sequence<Index...>) const {
std::array<std::size_t, sizeof...(Index)> size{};
auto begin = first;
while(begin != last) {
const auto entt = *(begin++);
((reg->template all_of<Component>(entt) ? ++size[Index] : 0u), ...);
}
(get<Component>(archive, size[Index], first, last), ...);
}
public:
/*! @brief Underlying entity identifier. */
using entity_type = Entity;
/**
* @brief Constructs an instance that is bound to a given registry.
* @param source A valid reference to a registry.
*/
basic_snapshot(const basic_registry<entity_type> &source) ENTT_NOEXCEPT
: reg{&source} {}
/*! @brief Default move constructor. */
basic_snapshot(basic_snapshot &&) ENTT_NOEXCEPT = default;
/*! @brief Default move assignment operator. @return This snapshot. */
basic_snapshot &operator=(basic_snapshot &&) ENTT_NOEXCEPT = default;
/**
* @brief Puts aside all the entities from the underlying registry.
*
* Entities are serialized along with their versions. Destroyed entities are
* taken in consideration as well by this function.
*
* @tparam Archive Type of output archive.
* @param archive A valid reference to an output archive.
* @return An object of this type to continue creating the snapshot.
*/
template<typename Archive>
const basic_snapshot &entities(Archive &archive) const {
const auto sz = reg->size();
archive(typename entity_traits::entity_type(sz + 1u));
archive(reg->released());
for(auto first = reg->data(), last = first + sz; first != last; ++first) {
archive(*first);
}
return *this;
}
/**
* @brief Puts aside the given components.
*
* Each instance is serialized together with the entity to which it belongs.
* Entities are serialized along with their versions.
*
* @tparam Component Types of components to serialize.
* @tparam Archive Type of output archive.
* @param archive A valid reference to an output archive.
* @return An object of this type to continue creating the snapshot.
*/
template<typename... Component, typename Archive>
const basic_snapshot &component(Archive &archive) const {
if constexpr(sizeof...(Component) == 1u) {
const auto view = reg->template view<const Component...>();
(component<Component>(archive, view.rbegin(), view.rend()), ...);
return *this;
} else {
(component<Component>(archive), ...);
return *this;
}
}
/**
* @brief Puts aside the given components for the entities in a range.
*
* Each instance is serialized together with the entity to which it belongs.
* Entities are serialized along with their versions.
*
* @tparam Component Types of components to serialize.
* @tparam Archive Type of output archive.
* @tparam It Type of input iterator.
* @param archive A valid reference to an output archive.
* @param first An iterator to the first element of the range to serialize.
* @param last An iterator past the last element of the range to serialize.
* @return An object of this type to continue creating the snapshot.
*/
template<typename... Component, typename Archive, typename It>
const basic_snapshot &component(Archive &archive, It first, It last) const {
component<Component...>(archive, first, last, std::index_sequence_for<Component...>{});
return *this;
}
private:
const basic_registry<entity_type> *reg;
};