Creé un código de muestra muy simple, solo una escena, un nodo sprite 20x20px, en el punto 0.0 en la pantalla. Cuando llamoscene.physicsWorld bodyAtPoint me devuelve este nodo incluso en el punto, por ejemplo: 34x34. Pero en el punto 35x35 vuelve.null. Básicamente, todos los puntos de 0px a 34px en ambos ejes devuelven este nodo, comenzando desde 35px, ya no lo devuelve. ¿Alguna idea de cuál podría ser la razón, si el sprite termina visiblemente a 20px 20px? El mismo comportamiento se ve enbodyInRect.

Aquí está el código de ejemplo:

-(id)initWithSize:(CGSize)size {    
if (self = [super initWithSize:size]) {
    /* Setup your scene here */

    self.backgroundColor = [SKColor colorWithRed:0.15 green:0.15 blue:0.3 alpha:1.0];
    self.physicsWorld.gravity = CGVectorMake(0, 0);

    SKSpriteNode *node = [[SKSpriteNode alloc] initWithColor:[UIColor whiteColor] size:CGSizeMake(20, 20)];
    node.position = CGPointMake(10, 10);

    node.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(20, 20)];
    [self addChild:node];

}
return self;
}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

for (UITouch *touch in touches) {
    CGPoint location = [touch locationInNode:self];
    if([self.physicsWorld bodyAtPoint:location])
    {
        NSLog(@"Detected at point: %f %f", location.x, location.y);
    }else{
        NSLog(@"No node at point: %f %f", location.x, location.y);
    }
}
}

Y aquí está el registro de la consola:

2013-11-09 15:05:52.822 SKTest[43143:70b] Detected at point: 2.000000 1.000000
2013-11-09 15:05:56.274 SKTest[43143:70b] Detected at point: 3.000000 7.000000
2013-11-09 15:05:57.006 SKTest[43143:70b] Detected at point: 3.000000 11.000000
2013-11-09 15:05:58.199 SKTest[43143:70b] Detected at point: 3.000000 12.000000
2013-11-09 15:05:58.918 SKTest[43143:70b] Detected at point: 3.000000 14.000000
2013-11-09 15:05:59.785 SKTest[43143:70b] Detected at point: 3.000000 17.000000
2013-11-09 15:06:00.685 SKTest[43143:70b] Detected at point: 3.000000 20.000000
2013-11-09 15:06:01.565 SKTest[43143:70b] Detected at point: 3.000000 22.000000
2013-11-09 15:06:02.915 SKTest[43143:70b] Detected at point: 3.000000 25.000000
2013-11-09 15:06:04.285 SKTest[43143:70b] Detected at point: 3.000000 30.000000
2013-11-09 15:06:05.387 SKTest[43143:70b] Detected at point: 3.000000 34.000000
2013-11-09 15:06:08.492 SKTest[43143:70b] No node at point: 4.000000 38.000000
2013-11-09 15:06:12.499 SKTest[43143:70b] Detected at point: 4.000000 5.000000
2013-11-09 15:06:13.240 SKTest[43143:70b] Detected at point: 6.000000 5.000000
2013-11-09 15:06:13.881 SKTest[43143:70b] Detected at point: 10.000000 5.000000
2013-11-09 15:06:15.064 SKTest[43143:70b] Detected at point: 12.000000 5.000000
2013-11-09 15:06:16.120 SKTest[43143:70b] Detected at point: 14.000000 5.000000
2013-11-09 15:06:16.873 SKTest[43143:70b] Detected at point: 16.000000 5.000000
2013-11-09 15:06:17.582 SKTest[43143:70b] Detected at point: 18.000000 5.000000
2013-11-09 15:06:18.066 SKTest[43143:70b] Detected at point: 21.000000 5.000000
2013-11-09 15:06:18.966 SKTest[43143:70b] Detected at point: 24.000000 5.000000
2013-11-09 15:06:19.585 SKTest[43143:70b] Detected at point: 31.000000 5.000000
2013-11-09 15:06:20.531 SKTest[43143:70b] Detected at point: 35.000000 5.000000
2013-11-09 15:06:22.581 SKTest[43143:70b] No node at point: 36.000000 4.000000
2013-11-09 15:06:26.560 SKTest[43143:70b] Detected at point: 19.000000 16.000000
2013-11-09 15:06:27.933 SKTest[43143:70b] Detected at point: 20.000000 17.000000
2013-11-09 15:06:29.856 SKTest[43143:70b] Detected at point: 25.000000 19.000000
2013-11-09 15:06:31.487 SKTest[43143:70b] Detected at point: 26.000000 22.000000
2013-11-09 15:06:33.850 SKTest[43143:70b] Detected at point: 29.000000 27.000000
2013-11-09 15:06:35.492 SKTest[43143:70b] Detected at point: 31.000000 29.000000
2013-11-09 15:06:36.854 SKTest[43143:70b] Detected at point: 35.000000 32.000000
2013-11-09 15:06:40.004 SKTest[43143:70b] No node at point: 40.000000 34.000000

¿Es posible que sea un error de Apple, tanto ennodeAtPoint ynodeInRect? Es difícil de creer. Pero el código es tan corto que no puedo ver dónde se pudo haber cometido algún error aquí. Cualquier ayuda será apreciada.