What's the best design for image-based iphone app?_问答_开发者

I would appreciate some advice on an iphone game design. I want to dis开发者_如何学运维play some backround image and other images on top of it (buildings, characters etc). The backround is going to be large (up to 10 times the size of the screen) so only a piece of the background file will be displayed at once. The idea is to replace this piece when character gets close to screen borders. I need to make this background transition as a smooth animation. Also, I need to have a zoom in/out feature, preferably animated. Some images on the screen will be static (buildings) and some will require some animation (character walking).

What is the best design:

Use Core Graphics combined with "sprite" classes - displaying sprite's UIImage with CGContextDrawImage
Use UIKit - create UIImageview to hold every image and add them as subviews in a single view appplication
Use OpenGL ES project

Option 1) turned out to be very slow. It seems like CoreGraphics is not meant to display images in a game loop. But maybe there is a way to make it effecient? Maybe combine it with Core Animation somehow?

Option 2) is my current choice. I am hoping the view to cache the image it holds and thus be more effecient than CG. But will the animation provided by UIImageview will be satisfactory? I think the views shouldn't be added all at once, but rather created & added (removed?) dynamically when background moves. Is it a good idea?

Option 3) would probably give the best control over the images but it seems like quite an overhead. I only need to display images, not vector graphics. Plus I'm new to Mac programming and I don't want to get stuck in some complex technology.

I appreciate any advice, thanks :)

I highly recommend Cocos2D as I've done my own development here on my blog. It was really easy to do. I follow Ray Wenderlich's tutorials and he provides great tools for doing everything you describe.

You asked "The backround is going to be large (up to 10 times the size of the screen) so only a piece of the background file will be displayed at once."

The tiled image system is very powerful and fast performance. If you use google maps you will see and example of a tiled image. Scroll off to a new are and blocks appear. In a local app you could take your image that is 10 times the size of the screen and cut in to tiles that are say 100px by 100px and each screen will only load the tiles that are displayed. When the user moves only the needed tiles are loaded. This saves memory and dramatically improves speed. It is the base reason why tables can fly, only the cells one screen are loaded, as is scrolls off the screen it's memory is reused for the next cell.

If option 2 is sufficiently performant for your needs I would stick with that - it's as easy a system as you'll get on the iPhone and fine for very simple graphics. A related option that might buy you a little bit of speed is using CALayers to implement the graphics. CALayers are almost as easy to use, but are a bit more lightweight than UIViews (in some ways you can think of UIViews as just wrappers for CALayers with additional overhead for managing things like touch events, etc.)

If you're interested I would read the Core Animation Programming Guide (I would provide a link but I think my reputation is too low, but Google should track it down for you). Core Animation is a big subject and can be pretty daunting but if you just use layers (i.e. not the animation parts of it) it's not so bad. Here's a quick example to give you a sense of what using layers looks like:

// NOTE: I haven't compiled this code so it may have typos/errors I haven't noticed

UIView* canvasView; // the view that will be the "canvas" for your game
... // initialize the canvas, etc.

CALayer* imageLayer = [CALayer layer];
UIImage* image = [UIImage imageNamed: @"MyImage.png"];
imageLayer.content = (id)image.CGImage;
imageLayer.bounds = CGRectMake(0, 0, image.size.width, image.size.height);
imageLayer.position = CGPointMake(100, 100); // NOTE: Unlike UIViews CALayers have their origin at the center
[canvasView.layer addSublayer:imageLayer];

So basically it looks a lot like working with views but with some added performance (and occasional headache).

P.S. - One thing to keep in mind is that if you make changes to a layer's property that is animatable (e.g. position, opacity, etc.) Core Animation will implicitly animate it (e.g. if you write imageLayer.position = somePoint; the layer animates to that position rather than having it's position set immediately. There's easy ways to work around that but that's a topic for another question/answer.