cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   sowbug
   Member

   I've read all the posts about how to integrate and build Box2d. I've successfully built test code for cocos2d and Box2d. But I want to make sure about one more thing. If you visit the CURRENT documentation webpage for Box2d (http://www.box2d.org/manual.html), you see stuff like this:

   b2CircleDef circleDef;
circleDef.radius = 3.0f;
circleDef.density = 2.5f;
b2Shape* myShape = myBody->CreateShape(&circleDef);

   As far as I can tell, the version of Box2d shipping with cocos2d 0.8.1 is newer than this, and it's completely incompatible (for example, b2Body no longer has a CreateShape method). Moreover, the documentation in svn has not been updated, so it seems that the new API has no documentation whatsoever (other than the source itself, of course).

   Have I correctly described the state of the world? If so, some questions:

   - Is there a version number for the version of Box2d that we cocos2d developers have? E.g., is it 2.1 or 3.0? It would be very helpful to start referring to this new version by a searchable name, other than just Google searches like [xcode cocos2d box2d broken hate angry].

   - Is there somewhere in the Box2d community that summarizes the API changes? For example, riq has helpfully published guides like "to migrate your code from version X of cocos2d to version Y, make the following five changes: [...]" Does something like that exist for Box2d?

   - Another question for those following the Box2d community: any idea why such drastic changes happened to the API? I'm sure they're great and very easy for any experienced Box2d developer to follow, but these changes broke every single tutorial and even the smallest Hello World apps out on the web, so the experience for novice Box2d developers like me has been pretty poor.

   Posted 2 years ago #
2. 

   cjl
   Member

   @sowbug

   I'm totally new to Box2d, and like you I found the API changes confusing. The updated API documentation is in SVN here:

   http://code.google.com/p/box2d/source/browse/trunk/Box2D/#Box2D/Documentation

   Anyway, you can read this:

   http://iphonedev.net/2009/07/12/cocos2d-example-box2d/

   That code in that blog post doesn't work with the new API, but there is an updated 'Hello World' here:

   http://code.google.com/p/box2d/source/browse/trunk/Box2D/Examples/HelloWorld/HelloWorld.cpp

   As a learning exercise I used the code from the updated Hello World to work my way through the blog post I referenced above. I think you will find doing the same helpful.

   Posted 2 years ago #
3. 

   sowbug
   Member

   Thanks, cjl. As far as I can tell, the API documentation you linked to is the same out-of-date documentation that confused me at first (it refers to CreateShape instead of CreateFixture, for example), but perhaps some of the less basic API usage has been updated, and I haven't noticed the difference yet because I'm still struggling with basic stuff.

   I'll use HelloWorld.cpp to get my stuff up and limping. Maybe by then I'll have climbed the hill and will be able to intuit the rest.

   Posted 2 years ago #
4. 

   chrisco
   Member

   I've just started with Box2d as well and tried to go through a tutorial on b2MouseJoints to allow dragging of Sprites. I ended up ditching my attempts in frustration because of the updated QueryAABB() (originally just World->Query(). I have absolutely no idea how to implement the b2QueryCallback() in my code, among the other differences.

   I had never really touched C++ before, and Obj-C++ has me completely baffled. I knew from the beginning that Box2D was going to be a challenge for me. So while I can get through it (and eventually understand it) by following a tutorial, I don't know enough to be able to figure out undocumented code on my own...

   Posted 2 years ago #
5. 

   Lam
   Member

   I went through cocos2d's test examples and they've certainly helped understanding the new API. I haven't used b2QueryCallback in my code yet but I just now see creating shapes as the old shape definitions and Fixtures are the new terms for Creating a shape.

   Though I like the new EdgeFixture since I've wanted box2d to have an edge line like chipmunks API, think "Line Rider" game, and now it does! :D

   ---
   box2D's version currently is 2.1.0 (found in: b2Settings.cpp)

   ---
   There isn't an easy documentation since the new changes are not part of the standard download but in the svn trunk. This is all subject to constant changes so if you don't want to keep changing your code, you could download the original release at box2d.org or look at the cocos2d Test example.

   ---
   The drastic changes was for easier creation of the b2world and to allow users to create shapes for collision detection without being dependent on the physics system. Erin Catto pretty much states it all here: http://www.box2d.org/forum/viewtopic.php?f=2&t=3201

   Posted 2 years ago #
6. 

   sowbug
   Member

   Thanks for the concise and direct answers, Lam. In particular, the thread from Erin helps me understand the scope of the changes. I've been reading more source code examples than documentation in the past few days, and that's been quite a bit less frustrating because they're generally correct.

   Posted 2 years ago #

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