Learning Cocos2D: Simple Collision Detection and Enemy AI

This chapter is from the book

Learning Cocos2D: A Hands-On Guide to Building iOS Games with Cocos2D, Box2D, and Chipmunk

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This chapter is from the book

This chapter is from the book 

Learning Cocos2D: A Hands-On Guide to Building iOS Games with Cocos2D, Box2D, and Chipmunk

Learn More Buy

Final Steps

The final step for this chapter is to make some changes to the GameplayLayer class so it loads the RadarDish and Viking onto the layer. Once these changes are made to the GameplayLayer files, you will have a working and playable version of Space Viking in your hands.

The GameplayLayer Class

The GameplayLayer class has a few changes to the header file. There is an additional import for the CommonProtocols.h file and the vikingSprite has been removed; instead there is a CCSpriteBatchNode called sceneSpriteBatchNode. Move your GameplayLayer.h and GameplayLayer.m files into the Layers Group folder in Xcode and ensure that your GameplayLayer.h header file has the same contents as Listing 4.10.

Listing 4.10. GameplayLayer.h header file

//  GameplayLayer.h
//  SpaceViking

#import <Foundation/Foundation.h>
#import "cocos2d.h"
#import "SneakyJoystick.h"
#import "SneakyButton.h"
#import "SneakyButtonSkinnedBase.h"
#import "SneakyJoystickSkinnedBase.h"
#import "Constants.h"
#import "CommonProtocols.h"
#import "RadarDish.h"
#import "Viking.h"

@interface GameplayLayer : CCLayer <GameplayLayerDelegate> {
    CCSprite *vikingSprite;
    SneakyJoystick *leftJoystick;
    SneakyButton *jumpButton;
    SneakyButton *attackButton;
    CCSpriteBatchNode *sceneSpriteBatchNode;
}

@end

The initJoystickAndButtons method of GameplayLayer stays the same as in Chapter 3. The rest of the GameplayLayer class requires changes to use the new CCSpriteBatchNode instance. Listings 4.11, 4.12, 4.13, and 4.14 cover the code for GameplayLayer.m. Replace the code in your GameplayLayer.m implementation file with the code in the next four listings.

Listing 4.11. GameplayLayer.m implementation file (part 1 of 4)

//  GameplayLayer.m
//  SpaceViking

#import "GameplayLayer.h"
@implementation GameplayLayer
- (void) dealloc {
    [leftJoystick release];
    [jumpButton release];
    [attackButton release];
    [super dealloc];
}

-(void)initJoystickAndButtons {
    CGSize screenSize = [CCDirector sharedDirector].winSize;       // 1
    // 2
    CGRect joystickBaseDimensions = CGRectMake(0, 0, 128.0f, 128.0f);
    CGRect jumpButtonDimensions = CGRectMake(0, 0, 64.0f, 64.0f);
    CGRect attackButtonDimensions = CGRectMake(0, 0, 64.0f, 64.0f);
    // 3
    CGPoint joystickBasePosition;
    CGPoint jumpButtonPosition;
    CGPoint attackButtonPosition;
    // 4
    if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
        // The device is an iPad running iPhone 3.2 or later.
        CCLOG(@"Positioning Joystick and Buttons for iPad");
        joystickBasePosition = ccp(screenSize.width*0.0625f,
                                   screenSize.height*0.052f);

        jumpButtonPosition = ccp(screenSize.width*0.946f,
                                screenSize.height*0.052f);

        attackButtonPosition = ccp(screenSize.width*0.947f,
                                   screenSize.height*0.169f);
    } else {
        // The device is an iPhone or iPod touch.
       CCLOG(@"Positioning Joystick and Buttons for iPhone");

        joystickBasePosition = ccp(screenSize.width*0.07f,
                                   screenSize.height*0.11f);

        jumpButtonPosition = ccp(screenSize.width*0.93f,
                                 screenSize.height*0.11f);

        attackButtonPosition = ccp(screenSize.width*0.93f,
                                   screenSize.height*0.35f);
    }

    SneakyJoystickSkinnedBase *joystickBase =
    [[[SneakyJoystickSkinnedBase alloc] init] autorelease];
    joystickBase.position = joystickBasePosition;
    joystickBase.backgroundSprite =
    [CCSprite spriteWithFile:@"dpadDown.png"];
    joystickBase.thumbSprite =
    [CCSprite spriteWithFile:@"joystickDown.png"];
    joystickBase.joystick = [[SneakyJoystick alloc]
                             initWithRect:joystickBaseDimensions];
    leftJoystick = [joystickBase.joystick retain];
    [self addChild:joystickBase];

    SneakyButtonSkinnedBase *jumpButtonBase =
    [[[SneakyButtonSkinnedBase alloc] init] autorelease];
    jumpButtonBase.position = jumpButtonPosition;
    jumpButtonBase.defaultSprite =
    [CCSprite spriteWithFile:@"jumpUp.png"];
    jumpButtonBase.activatedSprite =
    [CCSprite spriteWithFile:@"jumpDown.png"];
    jumpButtonBase.pressSprite =
    [CCSprite spriteWithFile:@"jumpDown.png"];
    jumpButtonBase.button = [[SneakyButton alloc]
                             initWithRect:jumpButtonDimensions];
    jumpButton = [jumpButtonBase.button retain];
    jumpButton.isToggleable = NO;
    [self addChild:jumpButtonBase];

    SneakyButtonSkinnedBase *attackButtonBase = [[[SneakyButtonSkinnedBase
alloc] init] autorelease];
    attackButtonBase.position = attackButtonPosition;
    attackButtonBase.defaultSprite = [CCSprite spriteWithFile:
@"handUp.png"];
    attackButtonBase.activatedSprite = [CCSprite
spriteWithFile:@"handDown.png"];
    attackButtonBase.pressSprite = [CCSprite spriteWithFile:
@"handDown.png"];
    attackButtonBase.button = [[SneakyButton alloc] initWithRect:
attackButtonDimensions];
    attackButton = [attackButtonBase.button retain];
    attackButton.isToggleable = NO;
    [self addChild:attackButtonBase];
}

The initJoystick method remains unchanged from previous chapters. The directional pad (DPad) as well as the jump and attack buttons are set up and added to the GameplayLayer. The high z values ensure that the joystick controls appear on top of all the other graphical elements in the GameplayLayer.

Listing 4.12. GameplayLayer.m implementation file (part 2 of 4)

#pragma mark –
#pragma mark Update Method
-(void) update:(ccTime)deltaTime {
    CCArray *listOfGameObjects =
            [sceneSpriteBatchNode children];                     // 1
    for (GameCharacter *tempChar in listOfGameObjects) {         // 2
        [tempChar updateStateWithDeltaTime:deltaTime andListOfGameObjects:
                     listOfGameObjects];                         // 3
    }
}

The update method is the run loop for the entire GameplayLayer. The CCSpriteBatchNode object contains a list of all of the CCSprites for which it will handle the rendering, batching their OpenGL ES draw calls. The update method does the following:

1. Gets the list of all of the children CCSprites rendered by the CCSpriteBatchNode. In Space Viking this is a list of all of the GameCharacters, including the Viking and his enemies.
2. Iterates through each of the Game Characters, calls their updateStateWithDeltaTime method, and passes a pointer to the list of all Game Characters. If you look back at the updateStateWithDeltaTime code in Viking.m, you can see the list of Game Characters used to check for power-ups and phaser blasts. Power-ups and aliens with phaser beams are covered in the next chapter.
3. Calls the updateStateWithDeltaTime method on each of the Game Characters. This call allows for all of the characters to update their individual states to determine if they are colliding with any other objects in the game.

The next section of code in GameplayLayer.m (Listing 4.13) contains the methods for creating the enemies and a placeholder for creating the phaser blast.

Listing 4.13. GameplayLayer.m implementation file (part 3 of 4)

#pragma mark -
-(void)createObjectOfType:(GameObjectType)objectType
              withHealth:(int)initialHealth
              atLocation:(CGPoint)spawnLocation
              withZValue:(int)ZValue {

    if (objectType == kEnemyTypeRadarDish) {
        CCLOG(@"Creating the Radar Enemy");
        RadarDish *radarDish = [[RadarDish alloc] initWithSpriteFrameName:
@"radar_1.png"];
        [radarDish setCharacterHealth:initialHealth];
        [radarDish setPosition:spawnLocation];
        [sceneSpriteBatchNode addChild:radarDish
                              z:ZValue
                              tag:kRadarDishTagValue];
        [radarDish release];
    }

}

-(void)createPhaserWithDirection:(PhaserDirection)phaserDirection
andPosition:(CGPoint)spawnPosition {
    CCLOG(@"Placeholder for Chapter 5, see below");
    return;
}

The createObjectOfType method sets up the RadarDish object using the CCSpriteBatchNode and adds it to the layer. This method is expanded upon in Chapter 5, "More Actions, Effects, and Cocos2D Scheduler," to include the other enemies in the Space Viking world.

The last code listing for GameplayLayer.m covers the init method. Copy the contents of Listing 4.14 into your GameplayLayer.m file.

Listing 4.14. GameplayLayer.m implementation file (part 4 of 4)

-(id)init {
    self = [super init];
    if (self != nil) {
        CGSize screenSize = [CCDirector sharedDirector].winSize;
        // enable touches
        self.isTouchEnabled = YES;

        srandom(time(NULL)); // Seeds the random number generator

    if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
        [[CCSpriteFrameCache sharedSpriteFrameCache]
          addSpriteFramesWithFile:@"scene1atlas.plist"];           // 1
        sceneSpriteBatchNode =
         [CCSpriteBatchNode batchNodeWithFile:@"scene1atlas.png"]; // 2
    } else {
        [[CCSpriteFrameCache sharedSpriteFrameCache]
          addSpriteFramesWithFile:@"scene1atlasiPhone.plist"];     // 1
        sceneSpriteBatchNode =
         [CCSpriteBatchNode
          batchNodeWithFile:@"scene1atlasiPhone.png"];             // 2
    }
        [self addChild:sceneSpriteBatchNode z:0];                  // 3
        [self initJoystickAndButtons];                             // 4
        Viking *viking = [[Viking alloc]
            initWithSpriteFrame:[[CCSpriteFrameCache
                sharedSpriteFrameCache]
                spriteFrameByName:@"sv_anim_1.png"]];              // 5
        [viking setJoystick:leftJoystick];
        [viking setJumpButton:jumpButton];
        [viking setAttackButton:attackButton];
        [viking setPosition:ccp(screenSize.width * 0.35f,
                                screenSize.height * 0.14f)];
        [viking setCharacterHealth:100];

        [sceneSpriteBatchNode
            addChild:viking
                   z:kVikingSpriteZValue
                 tag:kVikingSpriteTagValue];                       // 6

        [self createObjectOfType:kEnemyTypeRadarDish
                      withHealth:100
                      atLocation:ccp(screenSize.width * 0.878f,
                                     screenSize.height * 0.13f)
                      withZValue:10];                              // 7


        [self scheduleUpdate];                                     // 8
    }
    return self;
}
@end

Some key lines have been added since Chapter 2; they support the use of the CCSpriteBatchNode class and texture atlas:

1. Adds all of the frame dimensions specified in scene1atlas.plist to the Cocos2D Sprite Frame Cache. This will allow any CCSprite to be created by referencing one of the frames/images in the texture atlas. This line is also key in loading up the animations, since they reference spriteFrames loaded by the CCSpriteFrameCache here.
2. Initializes the CCSpriteBatchNode with the texture atlas image. The image scene1atlas.png becomes the master texture used by all of the CCSprites under the CCSpriteBatchNode. In Space Viking these are all of the GameObjects in the game, from the Viking to the Mallet power-up and the enemies.
3. Adds the CCSpriteBatchNode to the layer so it and all of its children (the GameObjects) are rendered onscreen.
4. Initializes the Joystick DPad and buttons.
5. Creates the Viking character using the already cached sprite frame of the Viking standing.
6. Adds the Viking to the CCSpriteBatchNode. The CCSpriteBatchNode does all of the rendering for the GameObjects. Therefore, the objects have to be added to the CCSpriteBatchNode and not to the layer. It is important to remember that the objects drawn from the texture atlas are added to the CCSpriteBatchNode and only the CCSpriteBatchNode is added to the CCLayer.
7. Adds the RadarDish to the CCSpriteBatchNode. The RadarDish health is set to 100 and the location as 87% of the screen width to the right (900 pixels from the left of the screen on the iPad) and 13% of the screen height (100 pixels from the bottom). The percentages are used instead of hard point values so that the same game will work on the iPhone, iPhone 4, and iPad. Although the screen width and height ratios between the iPhones and iPad are a little different, they are close enough to work for the placement of objects in Space Viking.
8. Sets up a scheduler call that will fire the update method in GameplayLayer.m on every frame.

Now that you have added code to handle the RadarDish, the Viking, and the texture atlas, it is time to test out Space Viking. If you select Run from Xcode, you should see the Space Viking game in the iPad Simulator, as shown in Figure 4.3.

Figure 4.3 Space Viking with the RadarDish in place