On the Line – Rocket Through - Cocos2d-x by Example Beginner's Guide - page 177

Time for action - adding the main loop
Let's implement our main update method.
1. In GameLayer.cpp , inside the update method, add the following lines:
if (!_running || _state != kGamePlay) return;
if (_lineContainer->getLineType() != LINE_NONE) {
_lineContainer->setTip (_rocket->getPosition() );
}
if (_rocket->collidedWithSides()) {
_lineContainer->setLineType ( LINE_NONE );
}
_rocket->update(dt);
//update jet particle so it follows rocket
if (!_jet->isActive()) _jet->resetSystem();
_jet->setRotation(_rocket->getRotation());
_jet->setPosition(_rocket->getPosition());
We check to see if we are not currently on pause. Then, if there is a line for our
ship that we need to show in _lineContainer , we update the line's tip point
with the _rocket current position.
We run collision checks between _rocket and the screen sides, update the
_rocket sprite, and position and rotate our _jet particle system to align it with
the _rocket sprite.
2. Next we update _comet (its countdown, initial position, movement, and collision
with _rocket if _comet is visible):
_cometTimer += dt;
float newY;
if (_cometTimer > _cometInterval) {
_cometTimer = 0;
if (_comet->isVisible() == false) {
_comet->setPositionX(0);