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iOS Build a Game with Sprite Kit Physics and Collision Contact Detection using SKPhysicsContactDelegate

Posted by Kelvin Atawura
.a{fill-rule:evenodd;}techdegree
Kelvin Atawura
Front End Web Development Techdegree Student 19,022 Points

skphysics

l tried creating the game differently. l have the enemies coming in from the right hand side and the hero on the right left corner with the machine. the idea is the enemies get hit by the projectile and hero gain points or the enemies get the machine and the hero loses point. my codes are as follows

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

    if (contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask) {
        firstBody = contact.bodyA;
        secondBody = contact.bodyB;
    } else {
        firstBody = contact.bodyA;
        secondBody = contact.bodyB;
    }

    if ( firstBody.categoryBitMask == RLCollisionCategoryEnemy && secondBody.categoryBitMask == RLCollisionCategoryProjectile ) {

        RLDogNode *dog = (RLDogNode *)firstBody.node;
        RLProjectileNode *projectile = (RLProjectileNode *)secondBody.node;
        [dog removeFromParent];
        [projectile removeFromParent];

    } else if (firstBody.categoryBitMask == RLCollisionCategoryEnemy && secondBody.categoryBitMask == RLCollisionCategoryMachine) {

        RLDogNode *dog = (RLDogNode*)firstBody.node;
        RLMachineNode *machine = (RLMachineNode *)secondBody.node;
        [dog removeFromParent];
        [machine removeFromParent];
    }



projectile physics
- (void) setupPhysicsBody {
    self.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:self.frame.size];
    self.physicsBody.affectedByGravity = NO;
    self.physicsBody.categoryBitMask = RLCollisionCategoryProjectile;
    self.physicsBody.collisionBitMask = 0;
    self.physicsBody.contactTestBitMask = RLCollisionCategoryEnemy;

}
machine physics
- (void) setupPhysicsBody {
    self.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:self.frame.size];
    self.physicsBody.affectedByGravity = NO;
    self.physicsBody.categoryBitMask = RLCollisionCategoryMachine;
    self.physicsBody.collisionBitMask = 0;
    self.physicsBody.contactTestBitMask = RLCollisionCategoryEnemy;

}

dog physics
- (void) setupPhysicsBody {
    self.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:self.frame.size];
    self.physicsBody.affectedByGravity = NO;
    self.physicsBody.velocity = CGVectorMake(-50, 0);
    self.physicsBody.categoryBitMask = RLCollisionCategoryEnemy;
    self.physicsBody.collisionBitMask = 0;
    self.physicsBody.contactTestBitMask = RLCollisionCategoryProjectile | RLCollisionCategoryMachine; 

}

and this code in the util.h file`typedef NS_OPTIONS(uint32_t, RLCollisionCategory) {
    RLCollisionCategoryEnemy        = 1 << 0, 
    RLCollisionCategoryProjectile   = 1 << 1,   
    RLCollisionCategoryDebris       = 1 << 2,   
    RLCollisionCategoryMachine      = 1 << 3   
};

so far l have hack my way for the projectile to get the enemies for them to disappear but they get throughout pass the machine without disappearing. is there anything am doing here? if yeah? please let me know Amit Bijlani

2 Answers

Michael Blazek
Michael Blazek
162 Points
Michael Blazek
Michael Blazek
162 Points

If I understand correctly, you should not be calling 

[machine removeFromParent];

So i would remove that line. You mentioned an error, but what is the error your getting?

Kelvin Atawura
.a{fill-rule:evenodd;}techdegree
Kelvin Atawura
Front End Web Development Techdegree Student 19,022 Points

The complier points at the machine pointer and then says unused variable

Michael Blazek
Michael Blazek
162 Points

That is just a warning that you declared a variable and did not use it in the scope of the block of code it was declared in. If you removed this line as well you would not get the warning:

RLMachineNode *machine = (RLMachineNode *)secondBody.node;
Kelvin Atawura
.a{fill-rule:evenodd;}techdegree
Kelvin Atawura
Front End Web Development Techdegree Student 19,022 Points

thanks that did work. one more question Micheal. how can i set it just at that point of contact the enemy disappears at now their body get pass the machine have way before they disappear

Michael Blazek
Michael Blazek
162 Points

Kelvin, it could have to do with the physics boxes you have set up on the objects. Seems like you changed the layout of the game, a ss of the new layout may help. If you can annotate what is going wrong that may help as well.

Kelvin Atawura
seal-mask
.a{fill-rule:evenodd;}techdegree
Kelvin Atawura
Front End Web Development Techdegree Student 19,022 Points
Kelvin Atawura
.a{fill-rule:evenodd;}techdegree
Kelvin Atawura
Front End Web Development Techdegree Student 19,022 Points

i havce been able to crack i get logs when they neck of the dog gets in contact with the machine. only problem now is they dog is removed from the parent since am using this code

else if (firstBody.categoryBitMask == RLCollisionCategoryEnemy && secondBody.categoryBitMask == RLCollisionCategoryMachine) {

        RLDogNode *dog = (RLDogNode*)firstBody.node;
        RLMachineNode *machine = (RLMachineNode *)secondBody.node;
        [dog removeFromParent];
        [machine removeFromParent];


    }

i tried removing the last line so that the machine doesn't move. but was ended up with an error. how can i resolve the please?
@[Amit Bijlani](https://teamtreehouse.com/amit)