ios - Sprite Kit Collision Detection

Question

Hi I am trying to setup collision detection in my game and I want to add collision detection so when the balloons hit the spikes they pop. I have looked at Ray Wenderliches tutorial but I couldn't figure it out because it didn't apply to my case. Any ideas how to set it up for my case?

The spikes are at the top of the screen and the balloons spawn at the bottom.

Answer 1

The basics for setting upp collision between 2 objects is to first setting upp constant that represent the different objects that can collide. I usually make a constants.h file where i keep all the variables that will be used thru out the game/application.

Declare following in either a constants.h file or just declare them as global variables in the class:

static const int balloonHitCategory = 1;
static const int spikeHitCategory = 2;

What you want to do now is set up the physics for both your balloon and spikes

SKSpriteNode *ballooon = [SKSpriteNode spriteNodeWithImageNamed:@"yourimagefilename"];
ballooon.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:yourSize];

ballooon.physicsBody.categoryBitMask = balloonHitCategory;
ballooon.physicsBody.contactTestBitMask = spikeHitCategory;
ballooon.physicsBody.collisionBitMask =  spikeHitCategory;

you should set your size and set your images for both of the spritenodes

SKSpriteNode *spikes = [SKSpriteNode spriteNodeWithImageNamed:@"yourimagefilename"];
spikes.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(yourSizeX, yourSizeY)];

spikes.physicsBody.categoryBitMask = spikeHitCategory;
spikes.physicsBody.contactTestBitMask = balloonHitCategory;
spikes.physicsBody.collisionBitMask =  balloonHitCategory;

for collision set up the following method:

-(void)didBeginContact:(SKPhysicsContact *)contact
{
    SKPhysicsBody *firstBody, *secondBody;

    firstBody = contact.bodyA;
    secondBody = contact.bodyB;

   if(firstBody.categoryBitMask == spikeHitCategory || secondBody.categoryBitMask == spikeHitCategory)
   {

       NSLog(@"balloon hit the spikes");
       //setup your methods and other things here 

   }
}

Before the collision will work you should also add the . In your scenes .h file add .

@interface myScene : SKScene <SKPhysicsContactDelegate>

@end

and in the .m file in the init function add:

-(id)initWithSize:(CGSize)size {    
    if (self = [super initWithSize:size]) {
    self.physicsWorld.contactDelegate = self;

    }
return self;
}

For more about collision handling check out apple documentation and adventure game example: https://developer.apple.com/library/ios/documentation/GraphicsAnimation/Conceptual/CodeExplainedAdventure/HandlingCollisions/HandlingCollisions.html#//apple_ref/doc/uid/TP40013140-CH5-SW1