Converting to Cocos2D. « cocos2d for iPhone

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Converting to Cocos2D.

(8 posts) (4 voices)

Started 1 year ago by infra_red
Latest reply from infra_red

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infra_red
Member

Hello,

I am posting a few questions to make sure that my research and assumptions are correct.
A little background first. I am a programmer. I have been one for all my adult life and i had a few dreams, one of which was to make games.
Rewind to 3 months ago ...
I have created several entertainment apps using UIKit for various clients and the time was right for me to make something really good. A game was something i always wanted to do and, with my partner, we decided it was what we wanted. We managed to find an investor who gave us a good sum of money in hard cash and we started.
We chose to use the Torque2D for iPhone engine.
Fast forward to the present day.
We have finished the game and it is really good. But there is a problem. Although it is perfect in iphone 3Gs and iPod Touch (all models) it crawls in 2g and 3g iPhones. Unfortunately Torque2D cannot handle even few objects at high motion speed if there is a background(!) on older iphones. The motion appears jerky even at 150 pixels per second linear speed ... I have tried all their optimizations and it simply doesn't work. For lesser velocities (up to 95 pixels per second) the motion is smooth.
You can realize that this is a huge problem as the game is based on speed. And we have the investor who gave his money too ...
So i took the difficult decision to rewrite using Cocos2d.
Questions:

- has anyone experience with high speed objects (up to 400 pixel/second linear velocities) with full screen backgrounds? Is there any slowdown ? Is the motion smooth ?
- I see that Cocos2d is licensed in LGPLv3 with the static compilation and source code inclusion additions. I interpret this to mean that i can use it for commercial titles, right ? (i know just making absolutely sure)
- We will mention the engine used in the credits (and possibly the start up sequence) so according to the license of Cocos Denshion, we can use that too... Right ? (i know, just making absolutely sure)
- Which is quicker to implement for collision detection ? Box2d or Chimpmunk ? what are your personal preferences ? Why ?
- Chimpmunk guys charge 200 USD for their Objective Chimpmunk library. Does Cocos2d use that (obligating us to pay this fee) or it uses the plain C++ version which means that we don't have to pay the fee ?

As a side note : the Torque engine is very nice and automated with several features that Cocos2d could duplicate. Too bad it doesn't work on the iphone ...

Posted 1 year ago #
zenkimoto
Member

Welcome to the forums Infra_red. While I don't know the answer to all your questions, I know the answer to some.

- I see that Cocos2d is licensed in LGPLv3 with the static compilation and source code inclusion additions. I interpret this to mean that i can use it for commercial titles, right ? (i know just making absolutely sure)

Yes, you can use it for a commercial title. A bunch of commercial games are already written with Cocos2D. Check out this link: http://www.cocos2d-iphone.org/forum/forum/1

- We will mention the engine used in the credits (and possibly the start up sequence) so according to the license of Cocos Denshion, we can use that too... Right ? (i know, just making absolutely sure)

Maybe someone else can clarify me on this answer. But, my understanding is if you use CocosDenshion in your code, you must credit the Cocos2D engine. Otherwise, I don't see a mention that you must credit the Cocos2D engine in your game. But, IMHO, you should always credit the engine. :-) Riq and others have done a great job.

- Which is quicker to implement for collision detection ? Box2d or Chimpmunk ? what are your personal preferences ? Why ?
- Chimpmunk guys charge 200 USD for their Objective Chimpmunk library. Does Cocos2d use that (obligating us to pay this fee) or it uses the plain C++ version which means that we don't have to pay the fee ?

Now, I don't know about Box2d because I've only used Chipmunk. But I can tell you that I picked it up in no time from no experience at all. It was fairly easy to use. And the Chipmunk guys charge 200 bucks for a optimized version of their library for the iPhone. You don't have to use the optimized version. The C and the Objective-C wrapper can be used with no cost. (Box2D is C++)

Hope this helps.

Posted 1 year ago #
riq
Key Master

- has anyone experience with high speed objects (up to 400 pixel/second linear velocities) with full screen backgrounds? Is there any slowdown ? Is the motion smooth ?

I guess it should work OK. Just remember that usually 2d games has the fill-rate bottleneck. So, if you hit that limit, should you try with 16-bit textures (default is 32-bit textures)
http://www.cocos2d-iphone.org/wiki/doku.php/prog_guide:best_practices#improving_performance

- I see that Cocos2d is licensed in LGPLv3 with the static compilation and source code inclusion additions. I interpret this to mean that i can use it for commercial titles, right ? (i know just making absolutely sure)

Yes. You are able to code and distribute closed source games with cocos2d.

- We will mention the engine used in the credits (and possibly the start up sequence) so according to the license of Cocos Denshion, we can use that too... Right ? (i know, just making absolutely sure)

yes, unless your company have a revenue higher than $250.000 per year. In that case you should pay the CocosDenshion license.

- Which is quicker to implement for collision detection ? Box2d or Chimpmunk ? what are your personal preferences ? Why ?

Chipmunk and Box2d uses 2 different algorithm for collision detection.
I think chipmunk is faster when the objects have the same size, and Box2d is faster when your objects have different sizes.
Chipmunk info: http://code.google.com/p/chipmunk-physics/wiki/CollisionDetection

Chimpmunk guys charge 200 USD for their Objective Chimpmunk library. Does Cocos2d use that (obligating us to pay this fee) or it uses the plain C++ version which means that we don't have to pay the fee ?

cocos2d uses Chipmunk (the C version), and not Objetive-Chipmunk. From what I've seen, Objective-Chipmunk is a nice, easy to use Chipmunk wrapper coded in objective-c.

Posted 1 year ago #
Steve Oldmeadow
Administrator

@infra_red - it would be interesting to know what the issue with Torque is to determine if cocos2d will perform better. I assume your real issue is the frame rate is low on the iPhone and iPhone 3G and that is why your high speed motion doesn't look good.

The only thing I can think of is that Torque isn't batching their OpenGL calls, this would make sense given it wasn't originally designed for OpenGL. If that is the case then cocos2d will perform much better.

If I was you I would contract someone (like Riq) under NDA to do a proof of concept in cocos2d to show that you can get the performance you require before committing to a rewrite in cocos2d and then finding you have exactly the same issue as you had with Torque.

As for which physics engine - if you have high speed objects then Box2d's continuous collision detection and bullet mode might be of interest as it prevents tunnelling issues (i.e high speed objects passing through each other)

Posted 1 year ago #
infra_red
Member

Hi,

Thank you all for your replies.

@zenkimoto
Yes chimpmunk looks very understandable, but i took a peek in the recently posted tutorials for Box2D and it seems it is easy too. I will most probably go with the Box2D version because of the reasons mentioned below.

@riq
Thank you for your prompt and clear answers.
As far as performance is concerned please see below :

@Steve Oldmeadow
Yes the issue is that Torque maxes out at 40 ~ 42 fps on the older generation phones. High speed motion is thus jerky. I cannot comment on torque's source code as it is a closed source product which simply provides the source to the developer, but for me there is something really odd going on there. I don't think it has to do with batching. I came to the conclusion that the engine is very unoptimized. I will explain a small experiment i did that made abandon their engine altogether.
With their latest codebase (which is supposedly highly optimized) i created three sprites. Their dimensions where 32x32 and they where 32 bit with transparencies. I gave them a velocity of 50, 100 and 150 pixels along the x axis only and no collision checking other than bouncing back when they reached the screen borders. Frame rate was 60~62 fps and everything was smooth. Then i went on and added another sprite, 64x64 non transparent 32 bit and not moving, as a background. Guess what : 40 fps and the 150 pixels/s ball jerky. This is not normal. We are talking about 430k pixels per second !! I cannot believe that the iphone cannot sustain such a little fill rate ! At worse it should be able to push one complete redraw of its screen at 60fps (that would be 9.2M pixels/s).
I made another experiment. I compiled the Cocos2d-Chimpmunk template after adding a full screen background and multiplying by 500 the gravity vector instead of 200 in the accelerometer callback. Even with 15 sprites on screen and moving, the fps was pinned at 60 and the motion was smooth ...
Thank you for your answer for box2d, i will be using that.

Just for the sake of safety though i will try to replicate in cocos2d the exact setup with the exact same files i used for the torque experiment to be sure and have no surprises down the road.

I want to thank you again for helping out as we are really with our backs against the wall ...

Posted 1 year ago #
infra_red
Member

Hello,

Posting a little update.
Recreated the test scenario in Cocos2d. The results are fantastic. Everything works as expected in the old phones. 60fps and of course smooth motion with even the highest velocities that the in-object games ever get to. The switch is certain. a few questions though :

I am thinking that since i won't be using too much physics (just a few collisions) it could be a good idea not to use a physics package at all. In that case i would execute a house-keeping method once per frame. Do you think that scheduling a method on the scene with interval 0 is a good idea or i should do it some other way ?

if i go with box2d is it a good idea to call step() that way (ie a per frame scheduled scene method) or i should be better off some other way ?

Has Cocos2d any vector manipulation helper functions or i should write my own for the collision calculations ?

I find the included tests / examples very informative and you guys should take pride that your engine is just as usable and much more efficient than iTorque. Documentation is on the same level. Overall a great performance from your part against commercial competition which is there for many many years. Way to go !

Posted 1 year ago #
Steve Oldmeadow
Administrator

@infra_red - yes a scheduled tick/heartbeat that gets called every frame is a good idea and you can step the physics world from such a thing. Just look at how the Box2d demo project with the falling blocks sets things up.

There are lots of choices for vector manipulation. cocos2d has some, box2d has some, chipmunk has some - take your pick.

It is great to hear the documentation is on a par with Torque.

Posted 1 year ago #
infra_red
Member

@Steve Thank you.
As far as documentation is concerned actually Cocos is better. Although the reference is of equal quality and completeness, and the Cocos Wiki is a bit lacking in comparison with Torque's, if you factor that the examples bundled with Cocos are FAR superior than the Torque provided example (some people have even trouble making it compile/work) Cocos2D is by far the better choice.

Most of the time you have to dig in the forum to find out if/how something works with Torque. The time loss is infuriating especially since for somethings you HAVE to change the engine source...
With Cocos, so far, i always have a starting point in an example/test...

Keep up the good work.

After using both engines i believe that Torque for iPhone is a waste of time. That engine can make SOME types of games but these are a VERY small subset of everything that the hardware is capable of. The engine is unoptimized to the point that its strengths are unusable. The graphic editor, integrated physics and scripting are nice, but since having them means that the maximum FPS is always less than 45 on older phones, they are no good.

Posted 1 year ago #

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