Question

I have a pretty big view which is like 1000 x 1000. So I did clipToBounds = YES. Will this actually produce smaller bitmaps for the views?

Answer 1

I think probably not – you will still need to allocate the memory for the view, just not display it.

You will probably get a very slight performance increase as UIKit knows more about what / what not to draw.

However, you can answer this question yourself! Make a project that makes 1000 1000×1000 views and puts them on the screen. Then look at it’s memory usage in the profiler. Then do the same with clipToBounds set to YES and see it it’s changed!

I predict that it won’t but I’d be interested in the results – if you do it, please post them up here!

Thanks, Sam

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EDIT

After the very reasonable comment by mystify, I’ve tested it by doing the following:

1) Created a new XCode project – Window application

2) Used the following code :

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

    // Override point for customization after application launch
    [window setClipsToBounds:YES];
    [window makeKeyAndVisible];

    // Make some views
    for (int n = 0; n < 100000; ++n) {
        UIImageView *view = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image.jpg"]];
        [view setFrame:CGRectMake(0, 0, 1000, 1000)];
        [window addSubview:view];
        [view release];
    }

    return YES;
}

3) Built it

4) Ran it in Instruments – Object allocations from a fresh start of the simulator.

As predicted, no change – it takes about 16MB with clipsToBounds set to either YES or NO on the window.

However, there are still a few questions –

a) I used a UIImageView to make sure that I had content that needed to be drawn for the entire of my view – the UI layer might optimize differently for different subclasses of UIView.

b) I ran it in the simulator (I don’t have an iPhone handy, mine broke) – I’m 99% sure that it won’e be any different on a device but I also know that the simulator isn’t 100% accurate with memory leaks so it’s probably a good idea to test on a device as well.