Sprit Sheets Vs array of PNG files for animations

rameshmrthy · July 2012

I do lot of animations in my iOS app using UIImageView.animationImages by passing an array of UIImage objects to the method listed below for animation. Current my array of UIImage objects contains separate PNG files. I know I can do similar animations by using & passing a Sprite Sheet instead of passing an array of separate PNG files. What are the advantages of one over another or Sprite Sheets are meant for a different purpose?

- (void) startImageViewAnimation:(UIImageView *)imageView WithImages:(NSArray*)imageArray orBuildArrayWithImage:(NSString *)imageName duration:(CGFloat)duration repeatCount:(NSInteger)repeatCount soundFile:(NSString *)soundFile stopSoundAfterDuration:(CGFloat) stopSoundDuration
{

    if([imageName length] != 0)
    {
        NSMutableArray *array = [[NSMutableArray alloc] init];
        UIImage *image;
        int index = 1;
        NSString *string;
        do
        {
            string = [NSString stringWithFormat:@"%@%02d.png", imageName, index++];
            image = [UIImage imageNamed:string];
            if(image)
                [array addObject:image];
        } while (image != nil);

        imageView.animationImages = array;
        [array release];
    }
    else
    {
        imageView.animationImages = imageArray;
    }
    imageView.animationDuration = duration;
    imageView.animationRepeatCount = repeatCount;
    [imageView startAnimating];

    if([soundFile length] != 0)
    {
        [self loadSoundEffectAudio:soundFile];
    }
}

Duncan C · July 2012

I don't know of any support for sprite sheets in UIKit.

Where I've seen sprite sheets is in OpenGL, and in particular cocos2d.

OpenGL has a requirement that textures have pixel counts that are a power of 2 in both dimensions for some features to work. (specifically MIP mapping. OpenGL textures are much faster to render when they are a power of 2 even if you don't use MIP mapping.) However, if you have an image that is 1025x1025 pixels, you have to save it at 2048x2048 pixels in order to satisfy the power-of-two-size requirement. That wastes a heck of a lot of space. With sprite sheets, you can cut up that 2048x2048 texture size and put lots of small images in the "dead spaces", thus making maximum use of your memory.

Beware that UIView animation uses gobs of memory. You only want to use it for pretty small images. If you find yourself trying to create full-screen or nearly full-screen animations, you should look into using a video format like Quicktime instead, since those use compression and streaming and make MUCH more efficient use of limited RAM.

rameshmrthy · July 2012

Thanks Duncan. Information you provided is very helpful. I think I was not clear on the usage of sprite sheets and now it all makes sense. All my images used for UIView animations are very small and are used to animate characters on scenes and none of them are full screen. Thank you much for your time and feedback.

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Sprit Sheets Vs array of PNG files for animations

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