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 | Constructs an instance that is bound to a given registry. | |
| component | Puts aside the given components. | |
| entities | Puts aside all the entities from the underlying registry. | |
| operator= | Default move assignment operator. |
Source
Lines 30-149 in src/entt/entity/snapshot.hpp.
template<typename Entity>
class basic_snapshot {
/*! @brief A registry is allowed to create snapshots. */
friend class basic_registry<Entity>;
using traits_type = entt_traits<Entity>;
template<typename Component, typename Archive, typename It>
void get(Archive &archive, std::size_t sz, It first, It last) const {
archive(typename traits_type::entity_type(sz));
while(first != last) {
const auto entt = *(first++);
if(reg->template has<Component>(entt)) {
if constexpr(std::is_empty_v<Component>) {
archive(entt);
} else {
archive(entt, reg->template get<Component>(entt));
}
}
}
}
template<typename... Component, typename Archive, typename It, std::size_t... Indexes>
void component(Archive &archive, It first, It last, std::index_sequence<Indexes...>) const {
std::array<std::size_t, sizeof...(Indexes)> size{};
auto begin = first;
while(begin != last) {
const auto entt = *(begin++);
((reg->template has<Component>(entt) ? ++size[Indexes] : size[Indexes]), ...);
}
(get<Component>(archive, size[Indexes], 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 &&) = default;
/*! @brief Default move assignment operator. @return This snapshot. */
basic_snapshot & operator=(basic_snapshot &&) = 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();
auto first = reg->data();
const auto last = first + sz;
archive(typename traits_type::entity_type(sz));
while(first != last) {
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 {
(component<Component>(archive, reg->template data<Component>(), reg->template data<Component>() + reg->template size<Component>()), ...);
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;
};