Class basic_continuous_loader
Synopsis
#include <src/entt/entity/snapshot.hpp>
template<typename Entity>
class basic_continuous_loader
Description
Utility class for continuous loading.
A continuous loader is designed to load data from a source registry to a (possibly) non-empty destination. The loader can accommodate in a registry more than one snapshot in a sort of continuous loading that updates the destination one step at a time.
Identifiers that entities originally had are not transferred to the target. Instead, the loader maps remote identifiers to local ones while restoring a snapshot.
An example of use is the implementation of a client-server applications with the requirement of transferring somehow parts of the representation side to side.
- Template Parameters
Entity- A valid entity type (see entt_traits for more details).
Methods
| basic_continuous_loader overload | Constructs an instance that is bound to a given registry. | |
| basic_continuous_loader overload | Default move constructor. | |
| component | Restores components and assigns them to the right entities. | |
| contains | Tests if a loader knows about a given entity. | |
| entities | Restores entities that were in use during serialization. | |
| map | Returns the identifier to which an entity refers. | |
| operator= | Default move assignment operator. | |
| orphans | Destroys those entities that have no components. | |
| shrink | Helps to purge entities that no longer have a conterpart. |
Source
Lines 303-566 in src/entt/entity/snapshot.hpp.
template<typename Entity>
class basic_continuous_loader {
using traits_type = entt_traits<Entity>;
void destroy(Entity entt) {
if(const auto it = remloc.find(entt); it == remloc.cend()) {
const auto local = reg->create();
remloc.emplace(entt, std::make_pair(local, true));
reg->destroy(local);
}
}
void restore(Entity entt) {
const auto it = remloc.find(entt);
if(it == remloc.cend()) {
const auto local = reg->create();
remloc.emplace(entt, std::make_pair(local, true));
} else {
if(!reg->valid(remloc[entt].first)) {
remloc[entt].first = reg->create();
}
// set the dirty flag
remloc[entt].second = true;
}
}
template<typename Container>
auto update(int, Container &container)
-> decltype(typename Container::mapped_type{}, void()) {
// map like container
Container other;
for(auto &&pair: container) {
using first_type = std::remove_const_t<typename std::decay_t<decltype(pair)>::first_type>;
using second_type = typename std::decay_t<decltype(pair)>::second_type;
if constexpr(std::is_same_v<first_type, entity_type> && std::is_same_v<second_type, entity_type>) {
other.emplace(map(pair.first), map(pair.second));
} else if constexpr(std::is_same_v<first_type, entity_type>) {
other.emplace(map(pair.first), std::move(pair.second));
} else {
static_assert(std::is_same_v<second_type, entity_type>, "Neither the key nor the value are of entity type");
other.emplace(std::move(pair.first), map(pair.second));
}
}
std::swap(container, other);
}
template<typename Container>
auto update(char, Container &container)
-> decltype(typename Container::value_type{}, void()) {
// vector like container
static_assert(std::is_same_v<typename Container::value_type, entity_type>, "Invalid value type");
for(auto &&entt: container) {
entt = map(entt);
}
}
template<typename Other, typename Type, typename Member>
void update([[maybe_unused]] Other &instance, [[maybe_unused]] Member Type:: *member) {
if constexpr(!std::is_same_v<Other, Type>) {
return;
} else if constexpr(std::is_same_v<Member, entity_type>) {
instance.*member = map(instance.*member);
} else {
// maybe a container? let's try...
update(0, instance.*member);
}
}
template<typename Component>
void remove_if_exists() {
for(auto &&ref: remloc) {
const auto local = ref.second.first;
if(reg->valid(local)) {
reg->template remove<Component>(local);
}
}
}
template<typename Other, typename Archive, typename... Type, typename... Member>
void assign(Archive &archive, [[maybe_unused]] Member Type:: *... member) {
typename traits_type::entity_type length{};
archive(length);
entity_type entt{};
if constexpr(std::tuple_size_v<decltype(reg->template view<Other>().get({}))> == 0) {
while(length--) {
archive(entt);
restore(entt);
reg->template emplace_or_replace<Other>(map(entt));
}
} else {
Other instance{};
while(length--) {
archive(entt, instance);
(update(instance, member), ...);
restore(entt);
reg->template emplace_or_replace<Other>(map(entt), std::move(instance));
}
}
}
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_continuous_loader(basic_registry<entity_type> &source) ENTT_NOEXCEPT
: reg{&source}
{}
/*! @brief Default move constructor. */
basic_continuous_loader(basic_continuous_loader &&) = default;
/*! @brief Default move assignment operator. @return This loader. */
basic_continuous_loader & operator=(basic_continuous_loader &&) = default;
/**
* @brief Restores entities that were in use during serialization.
*
* This function restores the entities that were in use during serialization
* and creates local counterparts for them if required.
*
* @tparam Archive Type of input archive.
* @param archive A valid reference to an input archive.
* @return A non-const reference to this loader.
*/
template<typename Archive>
basic_continuous_loader & entities(Archive &archive) {
typename traits_type::entity_type length{};
entity_type entt{};
archive(length);
for(decltype(length) pos{}; pos < length; ++pos) {
archive(entt);
if(const auto entity = traits_type::to_entity(entt); entity == pos) {
restore(entt);
} else {
destroy(entt);
}
}
// discards the head of the list of destroyed entities
archive(entt);
return *this;
}
/**
* @brief Restores components and assigns them to the right entities.
*
* The template parameter list must be exactly the same used during
* serialization. In the event that the entity to which the component is
* assigned doesn't exist yet, the loader will take care to create a local
* counterpart for it.<br/>
* Members can be either data members of type entity_type or containers of
* entities. In both cases, the loader will visit them and update the
* entities by replacing each one with its local counterpart.
*
* @tparam Component Type of component to restore.
* @tparam Archive Type of input archive.
* @tparam Type Types of components to update with local counterparts.
* @tparam Member Types of members to update with their local counterparts.
* @param archive A valid reference to an input archive.
* @param member Members to update with their local counterparts.
* @return A non-const reference to this loader.
*/
template<typename... Component, typename Archive, typename... Type, typename... Member>
basic_continuous_loader & component(Archive &archive, Member Type:: *... member) {
(remove_if_exists<Component>(), ...);
(assign<Component>(archive, member...), ...);
return *this;
}
/**
* @brief Helps to purge entities that no longer have a conterpart.
*
* Users should invoke this member function after restoring each snapshot,
* unless they know exactly what they are doing.
*
* @return A non-const reference to this loader.
*/
basic_continuous_loader & shrink() {
auto it = remloc.begin();
while(it != remloc.cend()) {
const auto local = it->second.first;
bool &dirty = it->second.second;
if(dirty) {
dirty = false;
++it;
} else {
if(reg->valid(local)) {
reg->destroy(local);
}
it = remloc.erase(it);
}
}
return *this;
}
/**
* @brief Destroys those entities that have no components.
*
* In case all the entities were serialized but only part of the components
* was saved, it could happen that some of the entities have no components
* once restored.<br/>
* This functions helps to identify and destroy those entities.
*
* @return A non-const reference to this loader.
*/
basic_continuous_loader & orphans() {
reg->orphans([this](const auto entt) {
reg->release(entt);
});
return *this;
}
/**
* @brief Tests if a loader knows about a given entity.
* @param entt An entity identifier.
* @return True if `entity` is managed by the loader, false otherwise.
*/
[[nodiscard]] bool contains(entity_type entt) const ENTT_NOEXCEPT {
return (remloc.find(entt) != remloc.cend());
}
/**
* @brief Returns the identifier to which an entity refers.
* @param entt An entity identifier.
* @return The local identifier if any, the null entity otherwise.
*/
[[nodiscard]] entity_type map(entity_type entt) const ENTT_NOEXCEPT {
const auto it = remloc.find(entt);
entity_type other = null;
if(it != remloc.cend()) {
other = it->second.first;
}
return other;
}
private:
std::unordered_map<entity_type, std::pair<entity_type, bool>> remloc;
basic_registry<entity_type> *reg;
};