Change the z-order of subviews on the iPhone

Question

I'm developing a game. I'm using about 150 UIImageView to hold the graphics. I'm simulating a 3D enviroment, so i would like to change the z-order (how close is an object to the camera).

I know there exists : [superWindow exchangeSubviewAtIndex:i withSubviewAtIndex:j];

But for some reason it's not working, some of the subviews disappear an re-appear.

Now I just remove all subviews and add it again in the correct z-order, this is ok with 50 subviews (on a 2G iphone) but with 120 it takes half a second so the gameplay sucks (I dont have and 3GS so i didn't try there).

I'm using so many subviews because each one is a square, then i colored it, resize it and move it somewhere in the screen. I'm holding the subviews under a NSMutableArray...

Answer 1

The iPhone documentation often warns about multiple UIViews nested, as it has a large performance hit after a certain point. If you start getting into issues one option is to render your UIViews into an image and using that to lower the number of on-screen views, but if you're simulating 3D that probably isn't going to help much since your composite view would need re-rendering too often.

The iPhone has full support for OpenGL ES, which allows for a real 3D environment. Take a look at some of the samples and/or a good book on the topic and you'll find that it's much easier to simply use OpenGL.

Answer 2

If you don't want to take the plunge to OpenGL ES, as Timothy suggests, you might want to look at replacing the UIViews with CALayers and placing them within a CATransformLayer. CATransformLayer is new in iPhone OS 3.0, and it lets you do a true 3-D layout of the CALayers. You can then set the zPosition property on your CALayers to locate them in the Z plane of the CATransformLayer. For more on 3-D layout of CALayers, I direct you to this article.

You can even add a nice perspective effect on the overall CATransformLayer by setting the m34 element in the CATransform3D applied to that layer.

Changing from UIViews to CALayers is pretty straightforward, because their structures have much in common.

Answer 3

Consider using a 2D game library like Cocos2D. I'm pretty sure that supports Z-ordering, and the performance will be vastly better than using UIViews.