.net barcode generator suite 4: Your First Game in Objective-C

Creator Data Matrix 2d barcode in Objective-C 4: Your First Game

CHAPTER 4: Your First Game
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A boundary check prevents the player sprite from leaving the screen. Once again we have to take the player texture s contentSize into account, since the player position is at the center of the sprite image but we don t want either side of the image to be off the screen. For this, we calculate the imageWidthHalved and then use it to check if the newly updated player position is within the left and right border limits. The code may be a bit verbose at this point, but that makes it easier to understand. And that s it for with the player accelerometer input logic. NOTE: The contentSize width is not divided by two but rather multiplied by 0.5 in order to calculate imageWidthHalved. This is a conscious choice and leads to the same results because any division can be rewritten as a multiplication. The update method is called in every frame, and every piece of code that runs in every frame should be running at top speed. And since the ARM CPUs of the iOS devices don t support division operations in hardware, multiplications are generally a bit faster. It s not going to be noticeable in this case, but it s a good habit to get into since, unlike other (premature) optimizations, it doesn t make the code harder to read or maintain.
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This game isn t any good until we add something for the player to avoid. The DoodleDrop04 project introduces an abomination of nature: a six-legged man-spider. Who wouldn t want to avoid that As with the player sprite, you should add the spider.png to the Resources group. Then the GameScene.h file gets three new member variables added to its interface. A spiders CCArray whose class reference is shown in Listing 4 9, and the spiderMoveDuration and numSpidersMoved, which are used in Listing 4 12:
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@interface GameScene : CCLayer { CCSprite* player; CGPoint playerVelocity; CCArray* spiders; float spiderMoveDuration; int numSpidersMoved; }
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And in the GameScene init method add the call to the initSpiders method discussed next, right after scheduleUpdate:
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-(id) init { if ((self = [super init])) {
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CHAPTER 4: Your First Game
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[self scheduleUpdate]; [self initSpiders]; } return self; }
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After that a fair bit of code is added to the GameScene class, beginning with the initSpiders method in Listing 4 8, which is creating the spider sprites.
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Listing 4 8. For Easier Access, Spider Sprites Are Initialized and Added to a CCArray. -(void) initSpiders { CGSize screenSize = [[CCDirector sharedDirector] winSize]; // using a temporary spider sprite is the easiest way to get the image's size CCSprite* tempSpider = [CCSprite spriteWithFile:@"spider.png"]; float imageWidth = [tempSpider texture].contentSize.width; // Use as many spiders as can fit next to each other over the whole screen width. int numSpiders = screenSize.width / imageWidth; // Initialize the spiders array using alloc. spiders = [[CCArray alloc] initWithCapacity:numSpiders]; for (int i = 0; i < numSpiders; i++) { CCSprite* spider = [CCSprite spriteWithFile:@"spider.png"]; [self addChild:spider z:0 tag:2]; // Also add the spider to the spiders array. [spiders addObject:spider]; } // call the method to reposition all spiders [self resetSpiders]; }
There are a few things to note. I create a tempSpider CCSprite only to find out the sprite s image width, which is then used to decide how many spider sprites can fit next to each other. The easiest way to get an image s dimensions is by simply creating a temporary CCSprite. Note that I did not add the tempSpider as child to any other node. This means that its memory will be released automatically. This is in contrast to the spiders array I m using to hold references to the spider sprites. This array must be created using alloc; otherwise, its memory would be released and subsequent access to the sprites array would crash the app with an EXC_BAD_ACCESS error. And since I took control over managing the sprites array memory, I must not forget to release the spiders array in the dealloc method, as shown here:
-(void) dealloc { CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self); // The spiders array must be released, it was created using [CCArray alloc] [spiders release]; spiders = nil;
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