linkEntity(entity) {
        if (!this.isEntityLinked(entity)) {
            this._entities.push(entity);
        }
    }
/**
     * Add an entity into the engine
     * only linked entities are thinked and rendered
     * @param entity {Entity}
     */
Add an entity into the engine
only linked entities are thinked and rendered
@param entity {Entity}
Add an entity into the engine only linked entities are thinked and rendered @param entity { Entity }
linkEntity(entity) {
        if (!this.isEntityLinked(entity)) {
            this._entities.push(entity);
        }
    }
linkEntity ( entity ) { if ( ! this . isEntityLinked ( entity ) ) { this . _entities . push ( entity ) ; } }
Add an entity into the engine
 only linked entities are thinked and rendered
 @param entity {Entity}
Add an entity into the engine only linked entities are thinked and rendered @param entity { Entity }