Why are my SKPhysicsJoints not working?

Question

I have a SKSpriteNode fish and an extended SKSpriteNode class hook; I'm trying to join these together when they come in contact, and later have them move together. I am using this code :

[fish removeAllActions];
NSLog(@"Fish anchor is is (%f,%f)", fish.anchorPoint.x, fish.anchorPoint.y);

CGPoint hp = CGPointMake(self.hook.frame.size.width/2, 0);

fish.anchorPoint = CGPointMake(1, .5);

CGPoint hookPoint = [self.scene convertPoint:hp fromNode:self.hook];
NSLog(@"Current fish position  is (%f,%f)", fish.position.x, fish.position.y);

NSLog(@"Hook point is (%f,%f)", hookPoint.x, hookPoint.y);

SKAction *moveAction = [SKAction moveTo:hookPoint duration:.1];

SKAction * flip;
if (fish.direction)  //if going to the right, then turn -90 degrees
    flip = [SKAction  rotateToAngle:M_PI_4 duration:.1 ];
else
    flip = [SKAction  rotateToAngle:(-M_PI_2) duration:.1 ];

//[fish runAction:moveAction];
[fish runAction:[SKAction sequence:@[moveAction, flip]]];

SKPhysicsJointFixed *joint =
            [SKPhysicsJointFixed jointWithBodyA:self.hook.physicsBody
                                          bodyB:fish.physicsBody
                                         anchor:hookPoint];



[self.physicsWorld addJoint:joint];
NSLog(@"Joined");

I have the fish designed as such :

self.anchorPoint = CGPointMake(1, .05);
[self setFishSize:[self getRandomSize]];
self.xScale *= .3;
self.yScale *= .3;    
self.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:self.frame.size]; // 1
self.physicsBody.collisionBitMask = 0;
self.physicsBody.contactTestBitMask = hookCategory;
self.physicsBody.categoryBitMask = fishCategory;
self.physicsBody.usesPreciseCollisionDetection = true;

and the hook as such :

    _hook = [SKSpriteNode spriteNodeWithImageNamed:@"hook"];
    _hook.anchorPoint = CGPointMake(.5, 0);


    _hook.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:_hook.frame.size];

    _hook.position = CGPointMake(100, self.frame.size.height - self.hook.size.height/2);
    _hook.physicsBody.dynamic = YES;
    _hook.physicsBody.categoryBitMask = hookCategory;
    _hook.physicsBody.contactTestBitMask = fishCategory;
    _hook.physicsBody.collisionBitMask = 0;
    _hook.physicsBody.usesPreciseCollisionDetection = YES;
    _hook.physicsBody.affectedByGravity = false;
    _hook.physicsBody.allowsRotation = false;
    self.physicsWorld.gravity = CGVectorMake(0,0);
    self.physicsWorld.contactDelegate = self;

and yet when they are joined, and I move the hook, the fish does not come along. Are there any glaring mistakes I'm making?

Any help greatly appreciated.

score 1 · Answer 1 · answered Nov 12 '13 at 22:14

1

You should have the joint formation in an action block, I suggest something like this,

 SKPhysicsJointFixed *joint = [SKPhysicsJointFixed jointWithBodyA:self.hook.physicsBody bodyB:fish.physicsBody anchor:hookPoint];

 SKAction *createJoint = [SKAction runBlock:^{   
 [self.physicsWorld addJoint:joint];}]

 // run this action when the condition is met
 [fish runAction:[SKAction createJoint]];

Also I see that you are using a lot of collision customization (e.g. collision groups, rotation limitation etc.) I suggest you use the bare minimum (or non) to start and get that working and then add the customization one by one to ensure it all works.

answered Nov 12 '13 at 22:14

user2421700

149
8

thank you, I will try that. What is the difference between adding an action normally as opposed to doing it through an action block? – pikovayadama Nov 12 '13 at 22:24
This way you can also detach and remove the joint with an action so its free again. Since I assume the hook remains but the fish needs to detach from the hook and go to a basket or something. – user2421700 Nov 13 '13 at 19:31

Why are my SKPhysicsJoints not working?

1 Answers1