Shooting Lasers

Let’s give our spaceship the ability to shoot. To do this, we will create an array of blue laser sprites. On every touch event, we will pick a sprite from the array and animate it across the screen. We will use Cocos2d-x sprite move actions to achieve this.

10. In HelloWorldScene.h:

(a) Define the following constant:

#define MAX_PLAYER_PROJECTILES 10 //Max Number of Player Lasers

(b) Under private declarations add:

//Keep track of current Player projectile
int _playerProjectileCount;

//Player Laser sprites
cocos2d::CCSprite* _playerProjectiles[MAX_PLAYER_PROJECTILES];

//Handle touch events
void ccTouchesBegan(cocos2d::CCSet *touches, cocos2d::CCEvent *event);

//Standard sprite action finished Handler
void spriteMoveFinished(CCNode *sender);

11. In HelloWorldScene.cpp

(a) Under HelloWorld::init() right before the schedule updateGame call add:

		//Initialize Player projectile count
		_playerProjectileCount = 0;

		//Initialize Player projectile sprites
		for (int i = 0; i < MAX_PLAYER_PROJECTILES; ++i) {
			_playerProjectiles[i] = CCSprite::createWithSpriteFrameName(
					"playerlaser.png");
			_playerProjectiles[i]->setScale(SPRITE_SCALE_FACTOR);
			_playerProjectiles[i]->setVisible(false);
			_playerProjectiles[i]->setPosition(ccp(_player->getPositionX(),_player->getPositionY()+(_player->getScaleY()*_player->getContentSize().height)));
			this->addChild(_playerProjectiles[i]);
		}

		//Enable touch events
		this->setTouchEnabled(true);

(b) Implement the touch event handler by adding the HelloWorld::ccTouchesBegan(cocos2d::CCSet *touches, cocos2d::CCEvent *event ) method:

void HelloWorld::ccTouchesBegan(cocos2d::CCSet *touches,cocos2d::CCEvent *event) {
	//We can choose one of the touches to work with
	CCTouch* touch = (CCTouch*) (touches->anyObject());
	CCPoint location = touch->getLocation();

	//Pick laser sprite from the projectile array and run an action on it
	_playerProjectiles[_playerProjectileCount]->stopAllActions();
	_playerProjectiles[_playerProjectileCount]->setPosition(ccp(_player->getPositionX(),_player->getPositionY()+(_player->getScaleY()*_player->getContentSize().height)));
	_playerProjectiles[_playerProjectileCount]->setVisible(true);

	//Create a move action that is 0.4s long and moves the projectile starting from the player position to the top of the screen
	_playerProjectiles[_playerProjectileCount]->runAction(CCSequence::create(CCMoveTo::create(0.4f,ccp(_player->getPositionX(),_winHeight)),CCCallFuncN::create(this,callfuncN_selector(HelloWorld::spriteMoveFinished)),NULL));
	++_playerProjectileCount;

	//If reached the maximum number of sprites reset the the count to recycle the sprites
	if (_playerProjectileCount >= MAX_PLAYER_PROJECTILES) {
		_playerProjectileCount = 0;
	}
	CocosDenshion::SimpleAudioEngine::sharedEngine()->playEffect("shoot.wav");
}

(c) Implement the standard sprite move finished handler method HelloWorld::spriteMoveFinished(CCNode* sender) to hide the sprite once the move action finishes:

void HelloWorld::spriteMoveFinished(CCNode* sender) {
	sender->setVisible(false);
}

In the code above, we first initialized a set of laser projectile sprites that player spaceship can shoot. Next, we added the call to setTouchEnabled(…) method which tells Cocos2d-x to start sending touch events to our game. To handle touch events, we override the ccTouchesBegan(…) method. Every time a touch event happens, we take the next available sprite from the laser projectile array and create a Cocos2d-x move action for it. The move action simply scrolls the laser vertically across the screen until the laser is off the screen. We also play a shooting sound effect along with the move action. Finally, we implement the spriteMoveFinished(…) method which hides the laser sprite once it’s off the screen i.e. the move action finishes.

Build/deploy the project and you should be able to shoot lasers by tapping on the screen.

You can download the completed source code for this step from here.