One-sided platform « cocos2d for iPhone

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One-sided platform

(8 posts) (3 voices)

Started 1 year ago by steg90
Latest reply from eviljack

Tags:

Box2D

steg90
Member

Hi,

I've been looking at the one-sided platform example and the code is self-explanatory. The problem I have is in the PreSolve method, how to let it know about my fixtures I want to check when it is in a separate class. For instance one of my fixtures is named _playerFixture, this is in my MainGameLayer, the PreSolve method is in a class called MyContactListener, so how would it know about _playerFixture?

void MyContactListener::PreSolve(b2Contact* contact, const b2Manifold* oldManifold) {
b2Fixture *fixA = contact->GetFixtureA();
b2Fixture *fixB = contact->GetFixtureB();

if(fixA == _playerFixture ) <---- how can it see _playerFixture
{
}

// etc
}

Obviously I must have a design problem, any help/advice is much appreciated.

Regards,
Steve

Posted 1 year ago #
steg90
Member

Hi all,

Decided on creating a singleton object and store a reference to my main game layer in there, the contact listener class will have access to this singleton and thus the main game layer. I'm thinking of making the contact listener do callbacks back to my main game layer when such things as PreSolved are being called - what do you think, is this a way to do what I asked above?

Example:

Global *pGlobal = [Global instance];

pGlobal._pMainGameLayer = self;

Where Global is my singleton object.

and then in my contact listener class in the PreSolve method, something like:

oid MyContactListener::PreSolve(b2Contact* contact, const b2Manifold* oldManifold) {

[[Global instance]._pMainGameLayer checkContact:contact];

Regards,
Steve

Posted 1 year ago #
Questor
Member

Steve,

That is one way to do it. Another way would be to use the userdata pointer that is available in every box2d object to allow you to differentiate between different box2d fixtures, bodies, etc. Userdata is basically just a void pointer that you can use to point to anything you want. Even if you don't use userdata for that purpose, it is a good idea to get familiar with it as it a very useful and versatile feature of box2d.

Regards,
Q

Posted 1 year ago #
steg90
Member

Hi Q,

I do use userdata and set that to my player sprite, prob still is, how would the contact listener know that fixtureA or fixtureB is in fact, my player sprite?

Thanks,
Steve

Posted 1 year ago #
steg90
Member

Hi,

Got this working now using my Singleton. What I want to ask is, for every platform I have in my game, do I have to do a check on it in the PreSolve to do the one-sided collision, seems like a lot of fixtures would need checking - is there another way?

Regards,
Steve

Posted 1 year ago #
steg90
Member

Hi all,

As I've got around 20 plaforms(static bodies) in my level, I was wondering, do I need to do a check in my PreSolve method on every one of these in order to allow for one-sided platforms?

Regards,
Steve

Posted 1 year ago #
eviljack
Member

good question steg, I'm having the exact same problem. I know how to do it the brute force way but it seems like such a waste. I'm thinking about making a class and then checking to see if one of the contact bodies is of that type.

Posted 1 year ago #
eviljack
Member

I actually solved it using tags:

b2Fixture* fixtureA = contact->GetFixtureA();
b2Fixture* fixtureB = contact->GetFixtureB();

b2Body *bodyA = fixtureA->GetBody();
b2Body *bodyB = fixtureB->GetBody();

CCSprite *spriteA = (CCSprite *)bodyA->GetUserData();
int tagA = [spriteA tag];

CCSprite *spriteB = (CCSprite *)bodyB->GetUserData();
int tagB = [spriteB tag];

if (tagA !=TAG_PLATFORM && tagB !=TAG_PLATFORM)
return;

Posted 1 year ago #

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