gohan/entity.go

package gohan

import (
	"time"
)

// Entity is an entity identifier.
type Entity int

// NewEntity returns a new (or previously removed and cleared) Entity. Because
// Gohan reuses removed Entity IDs, a previously removed ID may be returned.
func NewEntity() Entity {
	w.entityMutex.Lock()
	defer w.entityMutex.Unlock()

	if len(w.availableEntities) > 0 {
		id := w.availableEntities[0]
		w.availableEntities = w.availableEntities[1:]
		w.allEntities = append(w.allEntities, id)
		return id
	}

	w.maxEntityID++
	w.allEntities = append(w.allEntities, w.maxEntityID)
	w.components = append(w.components, make([]interface{}, w.maxComponentID+1))

	for i := range w.systems {
		w.systemComponents[i] = append(w.systemComponents[i], make([]interface{}, w.maxComponentID+1))
	}
	return w.maxEntityID
}

// Remove removes the provided Entity's components, causing it to no
// longer be handled by any system.  Because Gohan reuses removed EntityIDs,
// applications must also remove any internal references to the removed Entity.
func (entity Entity) Remove() bool {
	w.entityMutex.Lock()
	defer w.entityMutex.Unlock()

	for i, e := range w.allEntities {
		if e == entity {
			w.allEntities = _removeAt(w.allEntities, i)

			// Remove components.
			for i := range w.components[entity] {
				w.components[entity][i] = nil
			}

			w.removedEntities = append(w.removedEntities, entity)
			return true
		}
	}
	return false
}

// AllEntities returns a slice of all active entities. To retrieve only the
// number of currently active entities, use CurrentEntities.
func AllEntities() []Entity {
	w.entityMutex.Lock()
	defer w.entityMutex.Unlock()
	allEntities := make([]Entity, len(w.allEntities))
	copy(allEntities, w.allEntities)
	return allEntities
}

var numEntities int
var numEntitiesT time.Time

// CurrentEntities returns the number of currently active entities.
func CurrentEntities() int {
	if time.Since(numEntitiesT) >= w.cacheTime {
		numEntities = len(w.allEntities)
		numEntitiesT = time.Now()
	}
	return numEntities
}

func _removeAt(v []Entity, i int) []Entity {
	v[i] = v[len(v)-1]
	return v[:len(v)-1]
}