I'd like to implement a (physical) string with a weight in iOS, that reacts to accelerometer input and colides against the view bounds.
What is the simplest way to do this? I would prefer to avoid using external frameworks like Box2D, unless of course a native solution is too complicated.
If you need it to accelerate under gravity and bounce realistically when it hits the edge, you'll need to use a physics framework (unless you feel like getting out a physics book and doing the equations yourself) as there's nothing like that built into UIKit.
I'd recommend you try Chipmunk instead of Box2D. I've found it easier to use with Cocoa as it's pure C and not C++. It also has an Objective-C wrapper, but the developer charges for it (the plain C library is free).
Here's a simple iPhone Chipmunk physics example I put together.
It uses the accelerometer and UIKit for drawing - just replace the crates with your own objects. (The accelerometer doesn't work in the simulator, you'll have to try it on a phone).
UPDATE: now you've added the image I realise you mean a bob on a string (I thought you meant a UILabel that falls around the screen, lol!). Here's another example that includes a tether between crates. If you use this plus the Chipmunk docs you should be able to figure out what to do.
You'll need to attach one end of the string to a static object, or one with infinite mass (not included in my example).
If you want a realistic string, you'll need to break it up into several short constraints instead of just one long one, but I suggest you start simple if you've not got much experience with physics libraries.
Related
If I was interested in getting across game development on the iPhone/iPAD any suggestions on which technology(s) to start looking into? In fact just a simple bullet on each of these technologies that highlight how it fits into typical game development would be great, as the reason for this question was me not understanding how these fit together. So in this case it's where do these roughly fit in here:
UIKit
Core Animation
QuartzCore
OpenGL
cocos2D
I was getting the impression that cocos2D would be the way to go, and it seems to be a simpler wrapper for OpenGL? Not sure where that leaves UIKit vs Core Animation vs QuartzCore then?
Ok well I will try to make a rather lengthy answer short: it depends.
Now for a few longer thoughts and explanations - this is long. If you won't read it to the end, make sure you read the last few sentences.
First I need to clarify that the "technologies" or API's you have listed are mostly concerned solely with graphics
(except UIKit which also handles input) and that is ok as long as you understand
that the graphics is only a part (and as of my experience I might add "minor") of
a whole game.
Besides the graphics, there will be quite a bit more to handle when doing a real game.
In order not to get a away from the question too much let me just throw in a few buzzwords:
game logic, AI, resource management, physics, interaction, networking (possibly), sound, etc.
My recommendation is to get a good book on the topic and dive in [1,2].
Now that I skimmed that, back to your question:
Basically, OpenGL and QuarzCore are the core technologies to "get something drawn on the screen". All other technologies are built on top of that. So in theory, if you want to go that
way, you can implement everything related to graphics output with OpenGL or QuarzCore alone (whereas you will have to account for the fact that QuarzCore is 2D drawing only, whereas OpenGL supports 3D also and 2D is really just a special case of 3D). I actually believe that Quarz is also built on top of OpenGL, but I'm unsure about that.
UIKit is built on top of those and using it does basically two things: a) avoid re-inventing the wheel and b) make creation of user interfaces easier, faster and more robust. Of course you could draw every button itself by specifying the coordinates of a quad and sending that to OpenGL for processing. Then you would have to check every user input if it hits your button and call an associated handler. However, just creating an UIButton instance (maybe even in IB) and specifying an on-click handler does remove quite a lot of work.
Bottom line: UIKit is perfectly suited for creating user interfaces. Plus it can be used together with OpenGL and QuarzCore. I use it for the user interface on iOS even in games.
Regarding Cocos2D: This one is a "game engine" built on top of OpenGL. As such it includes quite a lot of the stuff you would have to handle yourself when rolling your own OpenGL-based engine, i.e. scene management, sprites, texturing, meshes, resources etc. I believe it also has connections to physics and collision detection libraries. In order to understand what happens there, however, requires to learn how computer graphics and games work[1,2,3].
Bottom line: you would use Cocos2D for your (2D) game graphics and UIKit to do the user interface.
CoreAnimation then is for animating CoreGraphics stuff. It provides an easy interface, e.g. for smoothly sliding or rotating stuff around, encapsulating all the required calculations (interpolations, redrawing etc). Will not work with OpenGL - but I think Cocos2D will also have a wrapper for that.
Bottom line: Use for fancy user interface animations.
Having said all that and just merely skimming the top I didn't want to frighten you in the first place.
For your special game (and every game is special) you might well get away with just UIKit and CoreAnimiation for the graphics and it might well make a blockbuster game. They allow a lot of drawing to take place with an easy to use interface plus they don't require too deep background knowledge and are sufficiently performant for small projects.
If you have a great game idea, use the simplest possible graphics solution that will satisfy you and your players and realize it. Once you got it going, you can still improve it if necessary.
[1]http://www.mcshaffry.com/GameCode/
[2]http://www.gameenginebook.com/
[3]http://www.opengl.org/documentation/red_book/
I have image named "platform.png" that represents one brick for platform of a IPhone game. I have a cartoon character that will jump on this platform.
A series of platform.png will form one complete platform. These series will be generated by swiping finger across Iphone screen. When character will jump on this platform it should go down like elastic and bounce back up. Can anyone tell me how to do this ?
Thanks in advance.
What yo want is Collision Detection. I don't think using Cocos2d will be a great idea to use in this case because you want to show elastic and bounce effects which should seem real. For this, what I suggest, is using Box2d which clearly help in showing the effects in a natural way. Here Collision Detection can be handled in a separate class known as ContactListener. You can study Box2d and ContactListener here. In ContactListener you can generate these effects and this class is very easy to handle. Two or three months back I used the same to create my game Pogo Jump and believe me I was very easy to work on Box2d.
Good luck..!!
heye ,
you have two options for this , either use box-2d/chipmunk or dont.
If you have prior experience with Physics then i would say box-2d/chipmunk would look more realistic.
I'm working on a 2D game (kind of like a top down space shooter) for the iPhone using an engine very similar to cocos2d (not exactly though) on OpenGL ES. I'm trying to figure out how I'm going to do collision detection.
All the ships for my game are images, and the game will load the image as a texture onto the screen. I've got very very simple detection going already that basically just takes the rectangles of the images and checks to see if those collide and can do that just fine.
But, of course the ship isn't perfectly taking up the entire rectangle so there is whitespace in there. So my question is how am I supposed to account for that whitespace? Do I have to have the matrices of the ships stored? Or is there another way? I've also heard of possibly using the Chipmunk physics engine for collision detection? How would that work?
(1) regarding Chipmunk, the short answer is yes you should immediately download chipmunk, donate something to the bloke, and start learning about it.
Working with that for a day or so will basically answer all the questions you have. If you want to work with physics games you're going to need to get in to it.
(2) you ask about using an approximation ("just" a rectangle) instead of something more accurately shaped like your spaceships. In fact, you'll be perhaps amazed to learn, that is precisely how it is usually done in all your famous big-name games you've played since we were all kids! Indeed sometimes you might use little more than A DOT (!) to detect collisions.
What you'd probably do in production is try a more complicated model, and play with it for a few hours and see, is it actually any better to play with than your simple dot or rectangle model.
If you do want to make a more complicated model -- just make one! Build it up from three or four rectangles using your current system. Try them "all against each other", and have "one big one to check first" to see if it is even anywhere near each other (sort of a simple spatial hashing).
You will find that when you do it with Chipmunk, which as you now know you have to immediately begin after reading this message, you just build it up the same tedious way. It's not a magic bullet. But if you were going to use a "more complicated model" yes it is better to go with something standard, chipmunk, to do the work in - it will get done quicker and better. There is heaps to learn and you should hop to it!
(3) Unity is not just for 3D Finally if you want to do it the smart-ass grown up way, you'd have to use Unity3D which will let you access the very metal, the Nvidia physics on the chipset. Note that unity works perfectly for 2D games also - you just click one button in unity to use a 2D projection (many brand-name ifone 2D games are done exactly like that).
If you use that approach, you can (if you want) have "absolutely exact" physics, with every nook and cranny of your model modelled.
What is the downside to doing this? Ah hah ... well the thing is, you need superb actual 3D models of all the stuff in your game! (Like you see them building in the "how we made the movie" special features that come with your favourite Pixar blu-ray.) To do that you need things like autodesk, maya and the like. you would quite likely buy some models ready-made from a digital prop shop (no need to build "a chair" as it has been done 1000 times already and you can buy one for ten dollars).
(Unity3D is completely free to use for a few months while you see if it can make you money.)
Incidentally on the Chipmunk front --- you can just use Corona which is ridiculously easy to use and has chipmunk-like physics completely built in with zero effort on your part! You could have the whole game done in less time than it took to write this email. You could be selling your game already and thinking up the next one. Or, you could use "Cocos" which indeed has a chipmunk-like physics library built-in .. personally (just me) I do not like and won't touch cocos - but of course many games use it.
(It seems pointless, to me, using cocos which is a "for idiots" product, when you can just go ahead and use Corona, which is a "for idiots" product but stupendously easier to use, 1000x more solid, and probably literally 10x faster to finish your product and start making money.)
Noel Summary:
So in some sense using Unity3D (and hence, the actual nvidia physics on your computer's chips) is the ultimate solution if you want detailed nook-and-cranny collisions. Going down one step, Chipmunk is exactly, precisely what you should be using on the ifone/ipad for 2D physics -- it is precisely what is used in all the famous games we know so well. You have a bit of learning to do so hop to it - it's superfun. Finally go right ahead and just make your current model more complicated if you wish - roll your own by adding more rectangles!
And the fourth point is, be sure to remember that in games, astonishingly, you can often get away with remarkably simple physics (often SIMPLER!! than one rectangle - just a damn point - ie, simply measuring the distance between centers!) Fifthly after going to all the effort of testing more detailed physics, you would play test one against each other, and find out what is the simplest physics you can get away with.
1- let's say there is a box on the screen and as soon as it gets hit by another box it suppose to move. How can i detect (getting hit) on my box object? Is it a good idea to use an nstimer which runs every 0.1 seconds and looking for the location of other objects around itself?
2- What is the best way to display simple 2d animations?
Install the Cocos2d templates and then instead of using the standard Cocos2d template use either the Chipmunk or Box2d template. Box2d has the benefit of C++ where Chipmunk is C based. Both still use Objective-C though for a lot of stuff. Heres where Cocos2d is. Note: All three templates have animation abilities.
When you drag an iphone GUI element like a list, it scrolls in a physics correct way, and also has a nice bounce effect at the end.
I would like to write a GUI element in my game, without using UIKit. I wonder where is the code implementing this, and if I can use it instead of trying to write something similar.
Any ideas?
I think that a physics engine would be overkill for just animating a gui element (unless you already have a physics engine in your game).
You could try using animations but I've no experience of doing this without UIKit but I suppose you would start here?
If you didn't want to use Core Animation, I would take a look at Robert Penner's easing equations - they're in actionscript but are pretty simple to port to C and would be a good start to get your own animation code started.
Hope this helps,
Sam
You can perhaps use animations to achieve this, you can define animation paths for bouncing or doing whatever it is you need and activate them when needed. I think the example project MoveMe can help you out
I can recommend the O'Reilly book "Physics for Game Developers" by David Bourg, which has great coverage of algorithms and code for all sorts of simulations. You probably want to start with motion affected by drag for the flick and gradual slowing, then look at a spring model to simulate the damping at the end.
box2d is an open source project that provides a great 2d physics engine.
this library is used by Intel clutter, which is a nice physics oriented UI library that is capable of running on mobile devices. that means that box2d is already optimized for mobile platforms like the iphone.