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Sparrow and Box2D

(25 posts) (5 voices)

Started 1 year ago by ronaldmathies
Latest reply from dlakin

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ronaldmathies
Moderator

I have seen some topics that people were busy trying to get Sparrow to work with Box2D, but has anyone been successful?

I am really interested as to how people combine the two, since a few things are a bit confusing.

Does somebody have a sample as to how to achieve this (especially the collision detection)?

I have found some nice descriptions on how to add Box2D to an iPhone project but not how to integrate it with something like Sparrow:

http://blog.zincroe.com/2009/05/how-to-add-box2d-to-an-iphone-xcode-project/
http://blog.zincroe.com/2009/05/iphone-and-box2d/

Not only do i want it for a test project of mine but also i would like to add new project templates that contain this by default (along with a sample) which can be downloaded by everybody.

Posted 1 year ago #
freerunnering
Moderator

http://www.drobnik.com/touch/2010/05/physics-101-uikit-app-with-box2d-for-gravity/
We'll i'm trying to follow this guide to making a basic physics app with it first and then if i can add it repeatedly without a problem then try adding it to sparrow.

I don't think sparrow causes any problems to adding box2d it's just getting box2d itself to work in an xcode project that needs to work?

If i can add box2d easily after some practise i'll post a guide or a project template?

Posted 1 year ago #
ronaldmathies
Moderator

I think we are on the same level. I also don't expect sparrow to cause any problems, especially since people have managed to get it to work (at least, reading the existing topics).

Maybe these resources can also help you:

http://iphonedev.net/2009/07/12/cocos2d-example-box2d/
http://www.emanueleferonato.com/2009/01/27/box2d-tutorial-for-the-absolute-beginners/
http://code.google.com/p/crayonballdemo/downloads/list

tonight i will also try to add Box2D to my xCode project, if i can get it to work (at least compilable) i will post my findings here. Maybe in this way we can help each other

Posted 1 year ago #
ronaldmathies
Moderator

Nice addition, to understand sparrow better somebody created a whole range of video tutorials explaining Box2D, however these are meant to be used for Flash developers but they are very informative and very understandable even if you don't have any flash background. the tutorials are based on Box2D version 2.0 and some things have changed it is still quite usefull:

http://www.kerp.net/box2d/

Posted 1 year ago #
Holger
Administrator

Unfortunately i have no experience with Box2D, but having a look at these tutorials i am sure that the Sparrow has nothing against Box2D.

I'd go for an onEnterFrame listener to update the object states in Box2D as Emanuele Feronato does in the mentioned demo. Using the given SPEnterFrameEvent's passedTime property should help updating Box2D with the current time.

Hm, however, that's close to wild guessing.

Posted 1 year ago #
ronaldmathies
Moderator

Yes, that is what i also was thinking, but what i am wondering for example is how is the cooperation between the two with thing like:

What if a rotate an SPSprite for example, Box2D would need to know this for collision detection for example.

These are probably simple things but need some figuring out.. But hey, who doesn't love a challenge

Posted 1 year ago #
Holger
Administrator

Hm, i guess that in that case you will have to (possibly) subtract that very object from Box2D and re-add it or update it's properties when you are done rotating. Maybe the b2World class that manages all objects in Box2D's world will help you updating your objects state.

I'm looking forward to the results of your tests, Ronald! Good luck!

Posted 1 year ago #
baike
Moderator

The Box2D manual mentions:

"A variable time step produces variable results, which makes it
difficult to debug. So don't tie the time step to your frame rate (unless you really, really have to)."

I'm just starting to integrate Box2D into my game, so I'm guessing that means running off an NSTimer or some timer callback. Hopefully I can contribute something to this thread in the next few days.

Ronald, from what I have read, rather than rotate your sprite, I would apply a torque to whatever Box2D body is representing your sprite and then all the calculations will be performed by Box2D automatically. Then after the time step, you read the rotation back off the connected body and draw your sprite. I think if you treat it as though Sparrow is for the most part an observer of Box2D (apart from user input being converted to joints and impulses), then most of the work should be done for you.

I'm probably going to load my Box2D level data from plists to avoid most of the nasty looking Box2D initialization code. I'll let you know how I get on.

Posted 1 year ago #
ronaldmathies
Moderator

The rotation description you mention is indeed necessary when the rotation is caused by some physics result. However, in my test application i allow the user to rotate an object using his fingers, in that case i would need to notify Box2D that the object also has been given a different angle. So the whole rotation part is triggered by a user action.

I am a bit further now, i can compile my Sparrow project which includes Box2D, now onward with setting up the world and adding some bodies

As soon as i am sure that the Box2D setup works i will post a description here on how to add it yourself (well, at least for the people that want to use it).

Posted 1 year ago #
dlakin
Member

Thanks for doing this! I am very interested in using it for my current project. I would love one of your great templates to base my application off of!

Posted 1 year ago #
baike
Moderator

Maybe you can make joints at the user's fingertips (like the Testbed does).

Posted 1 year ago #
ronaldmathies
Moderator

Oke, i have been able to get Box2D to work using Sparrow. So here follows my test-setup for what i have done, and some questions. If you have the time then please take the time to read them and answer them. It would help me, and the Sparrow users who want to use the templates a lot.

My test-setup included the following:

1. Integrate Box2D with a Sparrow project
2. Adjust project settings so that it allows for the combination of Objective-C and C (since Box2D is written in C)
3. I created an SPSprite which represented a ball and a block in the screen which is fixed at a steady point but can be moved by user interaction.
4. Both have collision detection so that the ball will bounce of the block.
5. Setup a separate thread for handling the physical world. (updating the state)

So i have a few questions for the Sparrow community:

Box2D is by no means an xCode project, so it doesn't include any xCode project file which makes integrating it using a static library unusable in case Box2D upgrades it's source.

So how to integrate it using templates?

Scenario #1:

Include the latest version / trunk version (trunk is actually better since they have changed really a lot). Directly within the project.

Pros:

Getting started is very fast, when you create a project it should be able to run directly without any changes with a sample. You don't have to download anything else but only need to create an extra setting in your xCode settings.

Cons:

Upgrading to a newer version is not that difficult but it includes removing existing files and adding newer files.

Scenario #2:

Create a static library for a certain version (in this case i will probably only do the trunk version). And handle it the same way as i do with the Sparrow Framework.

Pros:

Method is the same so recognizable for the template user. When you want to upgrade you can overwrite the files in the same manner as Scenario #1.

Cons:

You are by default stuck with a certain version that i used for building the static library.

Anybody have a suggestion for a better scenario?

Which of the three scenarios would you prefer?

The existing Sparrow files need to be changed so that they are Objective-C / C compatible, this can be done in two different ways, adjusting the file setting (using the get info box) or by changing the file extension to be .mm instead of being .m, which would you prefer? The first has the advantage that the naming convention is the same as what you are used to now, but has the dis-advantage that if you forget to change the property that you will receive a large amount of compiling errors. Changing the extension has the advantage that xCode directly knows that it is a Objective-C / C file.

Are there things that i might have forgotten to think about, do you have other ideas, suggestions etc... ?

Posted 1 year ago #
Holger
Administrator

Hi Ronald,

now that's a lot of text and i can only assume a lot of testing! Thanks for having a look at this!

@Scenarios:
I would - for now - definitely go for Scenario #1. That way you don't waste time building libraries and managing stuff. I'd rather invest that time into the game. You can always extract a static library later, when the App is in a near-final state and the Box2D implementation you are using fits your needs.

@File Extensions:
I still do not fully understand your problem with the file extensions. Maybe you can give more details about that. As far as i know the *.mm extension was originally reserved for C++ files. I found this in Apple's Objective-C Intro:

"...The compiler recognizes Objective-C source files by the filename extension .m, just as it recognizes files containing only standard C syntax by filename extension .c. Similarly, the compiler recognizes C++ files that use Objective-C by the extension .mm...."
http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjectiveC/Introduction/introObjectiveC.html

hth,
Holger

Posted 1 year ago #
baike
Moderator

I'd prefer Scenario #1.

I think you meant C++ for Box2D, as Objective-C is a superset of C already. I think Chipmunk is done in C for anyone who'd prefer to avoid C++. Chipmunk also has an objective-C wrapper (for $200), but it does very little for anyone but those who won't touch C or C++ under any circumstance. I got a lot of slowdown in the Chipmunk demo, and none whatsoever in the Box2D one (I realise they render differently), so I'm going with Box2D.

Posted 1 year ago #
ronaldmathies
Moderator

About the scenarios, this is not meant for my game in particular but just for ease of use of the templates. I have experienced with the early version of the templates that needed manual installation that people make a lot of mistakes of putting the files in the correct location and setting up xCode. So indeed probably Scenario #1 is easier and saver.

About the file extensions:

xCode can recognize by file extension what type contents is inside for compiling purposes:

.m -> Objective-C (and only Objective-C)
.c -> C (and only C)
.mm -> Objective-C / C mixture

If you continue to use .m while using Box2D you need to change the a property* of the file to tell xCode that is actually a mixture of Objective-C / C. If you forget to change that property you will have compilation problems since it will not recognize the C code and it will flag it as being faulty.

* the property can be found here:
1. Select a .m file
2. Open the details window using the Get Info context menu item on the file.
3. Open the listing File Type
sourcecode.c.objc -> Objective-C
sourcecode.cpp.objcpp -> Objective-C / C mixture

Sparrow itself (the samples in particular since these are the files you change to add Box2D code) and my templates use the .m extension. So i need to choose one of the two options to make them compatible with the C code of Box2D.

One option is by changing the extension to .mm, but every file in the future you would create also need to get this extension (like Ball.mm, or a Brick.mm).

The other option is that i change the property of the file to say that the .m file is actually a mixture. However, if you create files in the future you would also need to set the property correctly.

Posted 1 year ago #
ronaldmathies
Moderator

@baike

Yes, this is purely for Box2D, the questions are more about what your preference would be on how to integrate it.

So far Scenario #1 is winning 3 v.s. 0

Posted 1 year ago #
dlakin
Member

Scenario #1 does sound pretty good. I have been looking at chipmunk vs box2d, and it looks like box2d is the path I want to take. Excited to grab a template from you, I was having some trouble integrating the trunk version today. The older version worked fine, but I would rather wait a bit longer for the newest release.

Posted 1 year ago #
ronaldmathies
Moderator

@dlakin

I hope i can get the templates finished this week, it will take some time since i need to decide what parts i will setup by default (like the physical world etc..) and i want to have a small piece of demo code so you have a head start.

So the following things will be included in the template:

1. Of course Box2D itself
2. Setting up the world with some default values (gravity, size, meter -> pixel conversion etc..)
3. Timer with method for updating the view (basic implementation)
4. Floor body (so objects wouldn't disappear directly)
5. A ball that bounces or something similar to that.

Posted 1 year ago #
dlakin
Member

Sounds great, thank you for putting it together!

Posted 1 year ago #
freerunnering
Moderator

First option sounds best.

Also i'd use .mm

Also another note, box 2d is written in c++, and the .mm file extensions and for objective c / c++ mixes not objective c / c mixes as i think those can just be handled with .m, openfeint also uses objective c / c++ hence why it needs .mm file extensions.

Also sparrow itself could be left alone, unless it's added to the framework itself like with cocos2d, as only files the use box2d, import "box2d.h", need to be changed to .mm not all the .m files in the project.

Posted 1 year ago #
ronaldmathies
Moderator

@freerunning

Yes, my mistake, it is indeed C++ and not C.. I also think that .mm is better since this is more obvious. And indeed, Sparrow itself doesn't have to change since Sparrow doesn't use any C++ classes directly.

Posted 1 year ago #
baike
Moderator

Here's a quick run down of what I had to do to get a basic Box2D project working:

1. Download Box2D (I got v2.1.2).
2. Start a new Sparrow Based Application project.
3. Change Game.m to Game.mm.
4. Go to Project->Edit Project Settings.
5. Under the build tab, search for "Header Search Paths".
6. Add the path to Box2D and check the recursive box.

Box2D's includes are like: #include <Box2D/Collision/b2BroadPhase.h> so I added a path to the folder one above the folder that contains Box2D.h. That way the includes are not trying to drill down further than intended.

7. Drag and drop the Box2D folder named "Box2D" that contains "Box2D.h" into your project's Classes group.
8. Add #import <Box2D/Box2D.h> to the top of Game.mm.

Now you should be good to go. I may make a very light wrapper for b2Body so I can keep most of my project files as .m and talk to Box2D through a few light wrappers.

Posted 1 year ago #
dlakin
Member

Thanks Baike for the steps, I tried that out tonight and I still seem to have a problem. Doesn't seem to see the box2d.h file. I have tried moving things around but it isn't working.

Posted 1 year ago #
baike
Moderator

Sorry to hear that, dlakin. Maybe my paths were confusing (as there are a lot of Box2D folders). If you find a Box2D folder that contains Collision, Common and Dynamics folders and the Box2D.h file, and that Box2D folder was at "/Users/dlakin/iPhone/Code/Physics/Box2D", then you would add a search path for "/Users/dlakin/iPhone/Code/Physics" and by checking recursive it would look like "/Users/dlakin/iPhone/Code/Physics/**". Then the include would start at the Physics folder, look around for a Box2D folder, open it up and then be able to see Collision and so forth (like in my example include from a previous post).

Posted 1 year ago #
dlakin
Member

Thanks for clarifying this! Looks like it is working now, just haven't had a chance to make anything yet.

Thanks baike

Posted 1 year ago #

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