Collision detection between layers - cocos2d-iphone

Question

I have a few layers, which holds CCSprites .
I have a main CCScene that is adding these layers at the start.
I have to check collision between sprites from different layers .
I know how to check a simple collision with CGRectContains , my problem is , that i need some kind of a class that holds all the sprites positions from all layers ,and to check each tick for collision.
Question: what is the right way to create such a class,that save/check sprites from all layers on the scene ?
THanks .

Answer 1

If you don't care about empty space, then you can just set self.contentSize for every layer. You can do it like this:
CGRect rect = CGRectNull;
for (CCNode *node in self.children) {
rect = CGRectUnion(rect, node.boundingBox);
}
self.contentSize = rect.size;
But if you care about empty space, then you need to use something like this:
// put it somewhere outside class implementation
static inline BOOL CCLayerIntersectsCCLayer(CCLayer l1, CCLayer l2) {
for (CCNode *n1 in l1.children) {
for (CCNode *n2 in l2.children) {
CGRect r1 = n1.boundingBox;
CGRect r2 = n2.boundingBox;
r1.origin = [l1.parent convertToNodeSpace:r1.origin];
r2.origin = [l2.parent convertToNodeSpace:r2.origin];
if (CGRectIntersectsCGRect(r1, r2)) {
return YES;
}
}
}
return NO;
}
But you must understand, that all sprites (even circles) are actually rectangles. So if you need very precise collision detection, then you should use box2d in your project. If you are interesting in this, here are some links to read:
Box2d
Intro to Box2D with Cocos2D 2.X Tutorial: Bouncing Balls
Box2D Tutorial for iOS: How To Use Box2D For Just Collision Detection with Cocos2D iPhone