gohan/entity.go

package gohan

import (
	"sync"
	"time"
)

// Entity is an entity identifier.
type Entity int

var entityMutex sync.Mutex

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

// RemoveEntity 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 (w *World) RemoveEntity(entity Entity) bool {
	entityMutex.Lock()
	defer entityMutex.Unlock()

	for i, e := range w.allEntities {
		if e == entity {
			w.allEntities = append(w.allEntities[:i], w.allEntities[i+1:]...)

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

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

var numEntities int
var numEntitiesT time.Time

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