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169 lines
4.5 KiB
169 lines
4.5 KiB
#ifndef ENTT_ENTITY_ENTITY_HPP
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#define ENTT_ENTITY_ENTITY_HPP
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#include "../config/config.h"
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namespace entt {
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/**
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* @brief Entity traits.
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*
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* Primary template isn't defined on purpose. All the specializations give a
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* compile-time error unless the template parameter is an accepted entity type.
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*/
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template<typename>
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struct entt_traits;
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/**
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* @brief Entity traits for a 16 bits entity identifier.
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*
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* A 16 bits entity identifier guarantees:
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*
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* * 12 bits for the entity number (up to 4k entities).
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* * 4 bit for the version (resets in [0-15]).
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*/
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template<>
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struct entt_traits<std::uint16_t> {
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/*! @brief Underlying entity type. */
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using entity_type = std::uint16_t;
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/*! @brief Underlying version type. */
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using version_type = std::uint8_t;
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/*! @brief Difference type. */
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using difference_type = std::int32_t;
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/*! @brief Mask to use to get the entity number out of an identifier. */
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static constexpr std::uint16_t entity_mask = 0xFFF;
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/*! @brief Mask to use to get the version out of an identifier. */
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static constexpr std::uint16_t version_mask = 0xF;
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/*! @brief Extent of the entity number within an identifier. */
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static constexpr auto entity_shift = 12;
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};
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/**
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* @brief Entity traits for a 32 bits entity identifier.
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*
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* A 32 bits entity identifier guarantees:
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*
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* * 20 bits for the entity number (suitable for almost all the games).
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* * 12 bit for the version (resets in [0-4095]).
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*/
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template<>
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struct entt_traits<std::uint32_t> {
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/*! @brief Underlying entity type. */
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using entity_type = std::uint32_t;
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/*! @brief Underlying version type. */
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using version_type = std::uint16_t;
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/*! @brief Difference type. */
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using difference_type = std::int64_t;
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/*! @brief Mask to use to get the entity number out of an identifier. */
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static constexpr std::uint32_t entity_mask = 0xFFFFF;
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/*! @brief Mask to use to get the version out of an identifier. */
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static constexpr std::uint32_t version_mask = 0xFFF;
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/*! @brief Extent of the entity number within an identifier. */
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static constexpr auto entity_shift = 20;
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};
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/**
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* @brief Entity traits for a 64 bits entity identifier.
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*
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* A 64 bits entity identifier guarantees:
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*
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* * 32 bits for the entity number (an indecently large number).
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* * 32 bit for the version (an indecently large number).
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*/
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template<>
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struct entt_traits<std::uint64_t> {
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/*! @brief Underlying entity type. */
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using entity_type = std::uint64_t;
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/*! @brief Underlying version type. */
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using version_type = std::uint32_t;
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/*! @brief Difference type. */
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using difference_type = std::int64_t;
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/*! @brief Mask to use to get the entity number out of an identifier. */
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static constexpr std::uint64_t entity_mask = 0xFFFFFFFF;
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/*! @brief Mask to use to get the version out of an identifier. */
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static constexpr std::uint64_t version_mask = 0xFFFFFFFF;
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/*! @brief Extent of the entity number within an identifier. */
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static constexpr auto entity_shift = 32;
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};
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/**
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* @cond TURN_OFF_DOXYGEN
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* Internal details not to be documented.
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*/
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namespace internal {
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struct null {
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template<typename Entity>
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constexpr operator Entity() const ENTT_NOEXCEPT {
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using traits_type = entt_traits<Entity>;
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return traits_type::entity_mask | (traits_type::version_mask << traits_type::entity_shift);
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}
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constexpr bool operator==(null) const ENTT_NOEXCEPT {
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return true;
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}
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constexpr bool operator!=(null) const ENTT_NOEXCEPT {
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return false;
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}
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template<typename Entity>
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constexpr bool operator==(const Entity entity) const ENTT_NOEXCEPT {
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return entity == static_cast<Entity>(*this);
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}
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template<typename Entity>
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constexpr bool operator!=(const Entity entity) const ENTT_NOEXCEPT {
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return entity != static_cast<Entity>(*this);
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}
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};
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template<typename Entity>
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constexpr bool operator==(const Entity entity, null other) ENTT_NOEXCEPT {
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return other == entity;
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}
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template<typename Entity>
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constexpr bool operator!=(const Entity entity, null other) ENTT_NOEXCEPT {
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return other != entity;
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}
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}
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/**
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* Internal details not to be documented.
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* @endcond TURN_OFF_DOXYGEN
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*/
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/**
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* @brief Null entity.
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*
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* There exist implicit conversions from this variable to entity identifiers of
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* any allowed type. Similarly, there exist comparision operators between the
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* null entity and any other entity identifier.
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*/
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constexpr auto null = internal::null{};
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}
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#endif // ENTT_ENTITY_ENTITY_HPP
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