I'm quickly prototyping an iPad game and have been using frame-based collision detection. It's very much needing per pixel collision detection. Is there an easy way to implement this or any guides I could look at to hacking together my own? Google only brings up people in my similar predicament which does not bode well.
Ok. We had a game where we needed this.
One solution which worked was doing glreadpixel. But on the 3G, after a point when we added more objects in the game it became a bottleneck. 3GS, iPad and new iPhone/iPod should perform a lot better. Remember to read more, as glReadPixel is very costly and blocking call. But experimenting won't hurt.
Later we chose to use our own collision maps with curves and lines to do terrain collision. Similar to Box2d.
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thank you so much for all the fast responses I truly appreciate it. I have another question I've been wondering about, so I am working mobile game and I want to keep the size as small as possible. So I wanted to know does using Unity particle effects, impact performance and game size? I was wondering, if i wanted to make a visual effect of breaking apart a GameObject when destroyed, should I use unity particle system to do so? or should I make an animation of that game object breaking and use that instead?
to summeize should I be making animation for things such as rain effects and confetti and fire effect instead of making them with the particle system? is there any drawback to using one over the other?
As TEEBQNE said it is your choice between animations and the particle system depending on what you need. If your team is small or you are a single developer it is best to opt for the particle system for the flexibility of changes and quick execution.
Optimising the particle system is not hard, just make sure you don't overdo the numbers and avoid some common mistakes. There is a list of the best practices for optimization on mobile games found here
You can also find some pretty good looking particles premade in the unity asset store, which are already optimized well.
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.
I am new to iPhone dev and would like to write a game that involves 2d collisions. Would somebody give me a conceptual overview on how the various frameworks interact in a typical 2d collision game?
The candidates I see mentioned so far are 2d packages such as quartz and cocos2d and physics engines such as chipmunk and box2d. What I am not extremely clear is the relationships among these in my context.
Thanks in advance for answering!
Quartz is a 2D graphics API by Apple. It's usually not used for performance-intensive games, because you can get better performance by using OpenGL directly or by using some thin framework made for games. (Which is what Cocos2D provides.) The collision stuff is independent on this debate, since the collisions are usually calculated without knowing anything about the graphic representation of the colliding objects.
The relationship between collision (or general physics) engines and the graphic layer is exactly the relationship between a model and a view in the MVC pattern. In each frame you move the physical world a bit forward (physics) and then you draw the objects on their new positions (graphics).
In reality the model and view sometimes blend a bit to make things faster, but in principle they are completely separate things. Which means you can pick any of the possible combinations of OpenGL, Quartz or Cocos2D as the graphics engine and Box2D or Chipmunk as the physics engine and get a decent game. I'm not sure how well do the particular combinations work in practice - if that was your question, then I've just wasted a few minutes of your life :-)
zoul got it right, I would just add this :
Cocos2d for iPhone provides samples including Box2D and Chipmunk if you want to try them and see how easy or hard they are to use. So you can go ahead and download Cocos2d, then play with the samples a bit to see if it fits your needs.
I want to create an iPhone/iPod game. I want it to be 3d, but I want to use sprites instead of OpenGL to do this (I assume this would be easier since I don't know OpenGL).
I was thinking of simply layering sprites over top of each other and changing their size to give an illusion of 3d. It doesn't need to be too convincing since the game will be somewhat cartoony.
How can I use sprites as an alternative to OpenGL on the iPhone platform?
You can use CoreAnimation for this. Either using UIImageViews (or plain UIViews) or CALayers.
It's usually the best choice for some types of 2d games (board games, for example), since animation, rotation and scaling are really easy. Just keep in mind that if performance is your concern, OpenGL will always be better.
Depending on how much 3d, I'd recommend taking a look at cocos2d. It supports multiple layers, sprites, animations, etc, but is pretty straightforward to pick up & learn. (Much easier than OpenGL to me) The example code is very comprehensive.
http://code.google.com/p/cocos2d-iphone/
I have built a game using core animation with upto about 17 - 20 objects floating about the screen scaling and rotating and performance was fine on the iPhone (make sure you check regularly on the iPhone as the simulator doesnt simulate iPhone memory or CPU speed).
CoreAnimation is pretty simple and really powerful. Use PNG's for images and I don't think you will have to many issues. The real killer of this will be alpha's in your images, this is hard work for the iPhone. So the less transparency you have the better you app will go.
In addition to Marco's answer I want to add: Not using OpenGL may also tax the device battery a little more. As I understand it, OpenGL ES can be more efficient on a device power supply (if implemented properly). Of course, this depends on how much animation is going to be used with UIImageView, UIView or CALayers, etc.
I'm sure there is a tipping point.
OK, I'm still brand new to iPhone development. I have a free game on the app store, Winner Pong, but it's just a Pong clone (who would've guessed) that uses the standard UIImageViews for the sprites. Now I want to do something a little more complicated, and port my game for the Xbox 360, Trippin Alien, to the iPhone. I obviously can't keep using UIImageViews, so I was wondering which would be better to learn: the simpler, but performance-hindering Qurtz2D, or the smooth-running but dauntingly complex OpenGL ES.
My game is basically a copter game, with about 8-10 sprites on screen plus a simple particle system (video here). Not too complicated, but performance does matter. My only prior game programming experience is in Microsoft's XNA and C#, which has a built in SpriteBatch framework that makes it incredibly easy to draw, scale, and rotate pre-rendered sprites on screen. Is it worth it to learn OpenGL ES? How big is the performance gap? Is quartz really that simple?
Also, if anyone knows of any tutorials for either one, please, post them here. I need as much help as I can get.
Look through code samples of each to actually see the complexity. You might find that OpenGL isn't so daunting.
Regarding the performance. Core Animation, which Quartz2d is part of, uses OpenGL behind the covers, so for simple sprite animations, I would expect your game to perform fairly well.
I would also glance over the programming guide for each before making your final decision.
Another alternative is to use something like Unity. I recently just started playing around with the trial version of this development environment and if you're mostly doing game development with graphical objects and sprites, this may be one option to consider. You can script in C#, Javascript, or Boo. The development environment allows you to graphically setup your scenes and levels. You can then attach scripts to graphical objects for animation to handle user events, etc.
One downside for Unity, which I've heard from others is that if you want to use the familiar UI controls from UIKit, it's not so easy to instantiate them...I haven't verified this myself.