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https://github.com/onevcat/APNGKit

High performance and delightful way to play with APNG format in iOS.
https://github.com/onevcat/APNGKit

apng apng-image swift

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High performance and delightful way to play with APNG format in iOS.

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README 

        


APNGKit





















APNGKit is a high performance framework for loading and displaying APNG images in iOS and macOS. It's built with 

high-level abstractions and brings a delightful API. Since be that, you will feel at home and joy when using APNGKit to 

play with images in APNG format.



## APNG, what and why?



The [Animated Portable Network Graphics (APNG)](https://en.wikipedia.org/wiki/APNG) is a file format extending the 

well-known PNG format. It allows for animated PNG files that work similarly to animated GIF files, while supporting 

24-bit images and 8-bit transparency not available for GIFs. This means much better quality of animation. At the same 

time, the file size is comparable to or even less than, if created carefully, GIFs.



Talk is cheap; show me the image. You can click on the image to see how it looks like when animating.





APNGKit Demo




That's cool. APNG is much better! But wait...why haven't I heard about APNG before? It is not a popular format, so why 

should I use it in my next great iOS/macOS app?



Good question! APNG is an excellent extension for regular PNG, and it is also very simple to use and not conflicting 

with current PNG standard (It consists a standard PNG header, so if your platform does not support APNG, it will be 

recognized as a normal PNG with its first frame being displayed as a static image). But unfortunately, it is a rebel 

format so that it is not accepted by the PNG group. However, it is accepted by many vendors and is even mentioned in 

[W3C Standards](http://www.w3.org/TR/html5/embedded-content-0.html#the-img-element). There is another format called 

MNG (Multiple-image Network Graphics), which is created by the same team as PNG. It is a comprehensive format, but very 

very very (ι‡θ¦ηš„δΊ‹θ¦θ―΄δΈ‰ι) complex. It is so complex that despite being a "standard", it was almost universally rejected.

There is only one "popular" browser called [Konqueror](https://konqueror.org)(at least I have used it before when I was 

in high school) that supports MNG, which is really a sad but reasonable story.



Even though APNG is not accepted currently, we continue to see the widespread implementation of it. Apple recently 

supported APNG in both [desktop and mobile Safari](http://www.macrumors.com/2014/09/28/ios-8-safari-supports-animated-png-images/). 

Microsoft Edge and Chrome are also considering adding APNG support since it is already officially added in 

[WebKit core](https://bugs.webkit.org/show_bug.cgi?id=17022).



APNG is such a nice format to bring users much better experience of animating images. The more APNG is used, the more 

recognition and support it will get. Not only in the browsers world, but also in the apps we always love. That's why 

I created this framework.



## Installation



### Requirement



iOS 9.0+ / macOS 10.11+ / tvOS 9.0+



### Swift Package Manager



The **recommended way** to install APNGKit is to use Swift Package Manager. Adding it to your project with Xcode:



- File > Swift Packages > Add Package Dependency

- Add https://github.com/onevcat/APNGKit.git

- Select "Up to Next Major" with "2.0.0"



### CocoaPods



[CocoaPods](http://cocoapods.org) is a dependency manager for Cocoa projects.



```bash

$ gem install cocoapods

```



To integrate APNGKit into your Xcode project using CocoaPods, specify it in your `Podfile`:



```ruby

source 'https://github.com/CocoaPods/Specs.git'

platform :ios, '9.0'

use_frameworks!



target 'your_app' do

 Β pod 'APNGKit', '~> 2.0'

end

```



Then, run the following command:



```bash

$ pod install

```



You should open the `{Project}.xcworkspace` instead of the `{Project}.xcodeproj` after you installed anything from CocoaPods.



For more information about how to use CocoaPods, I suggest [this tutorial](http://www.raywenderlich.com/64546/introduction-to-cocoapods-2).



## Usage



### Basic



Import APNGKit into your source files in which you want to use the framework.



```swift

import APNGKit

```



#### Load an APNG Image



```swift

// Load an APNG image from file in main bundle

var image = try APNGImage(named: "your_image")



// Or

// Load an APNG image from file at specified path

if let url = Bundle.main.url(forResource: "your_image", withExtension: "apng") {

    image = try APNGImage(fileURL: path)

}



// Or

// Load an APNG image from data

let data: Data = ... // From disk or network or anywhere else.

image = try APNGImage(data: data)

```



You may notice that all initializers are throwable. If anything is wrong during creating the image, it let you know the 

error explicitly and you have a chance to handle it. We will cover the error handling soon later.



#### Display an APNG Image



When you have an `APNGImage` object, you can use it to initialize an image view and display it on screen with an 

`APNGImageView`, which is a subclass of `UIView` or `NSView`:



```swift

let image: APNGImage = ... // You already have an APNG image object.



let imageView = APNGImageView(image: image)

view.addSubview(imageView)

```



#### Start animation



The animation will be played automatically as soon as the image view is created with a valid APNG image. If you do not

want the animation to be played automatically, set the `autoStartAnimationWhenSetImage` property to `false` before you 

assign an image:



```swift

let imageView = APNGImageView(frame: .zero)

imageView.autoStartAnimationWhenSetImage = false

imageView.image = image



// Start the animation manually:

imageView.startAnimating()

```



#### XIB or Storyboard



If you are an Interface Builder lover, drag a `UIView` (or `NSView`) (Please note, not a `UIImageView` or `NSImageView`) 

to the canvas, and modify its class to `APNGImageView`. Then, you can drag an `IBOutlet` and play with it as usual, such

as setting its `image` property.



### Delegates



APNG defines the play loop count as `numberOfPlays` in `APNGImage`, and APNGKit respects it by default. To inspect the 

end of each loop, register yourself as a delegate of `APNGImageView.onOnePlayDone`:



```swift

class ViewController: UIViewController {

    override func viewDidLoad() {

        super.viewDidLoad()



        let imageView = APNGImageView(image: image)

        imageView.onOnePlayDone.delegate(on: self) { (self, count) in

            print("Played: \(count)")

        }

    }

}

```



When `numberOfPlays` is `nil`, the animation will be played forever. If it is a limited non-zero value, the animation 

will be stopped at the final frame when the loop count reaches the limit. To inspect the whole animation is done, 

use `onAllPlaysDone`:



```swift

imageView.onAllPlaysDone.delegate(on: self) { (self, _) in

    print("All done.")

}

```



APNGKit loads the data in a streaming way by default, it reads the frame information while playing the animation. Since

APNG encodes the duration in each frame, it is not possible to get the whole animation duration before loading all frames 

information. Before the first reading pass finishes, you can only get a partial duration for loaded frames. To get the

full duration, use `APNGImage.onFramesInformationPrepared`:



```swift

let image = try APNGImage(named: "image")

image.onFramesInformationPrepared.delegate(on: self) { (self, _) in

    switch image.duration {

        case .full(let duration):

            print("Full duration: \(duration)")

        case .partial:

            print("This should not happen.")

    }

}



imageView.image = image

```



Or, you can specify the `.fullFirstPass` option while creating the `APNGImage`. It reads all frames before starting 

rendering and animating the image:



```swift

let image = try APNGImage(named: "image", options: [.fullFirstPass])

print(image.duration) // .full(duration)

```



APNGKit provides a few other reading options. Please let me skip it for now and you can check them in documentation.



### Error handling



#### While creating image



Creating an `APNGImage` can throw an error if anything goes wrong. All possible errors while decoding are defined as an

`APNGKitError.decoderError`. When an error happens while creating the image, you are expected to check if it should be 

treated as a normal static image. If so, try to set it as the static image:



```swift

do {

    let image = try APNGImage(named: data.imageName)

    imageView.image = image

} catch {

    if let normalImage = error.apngError?.normalImage {

        imageView.staticImage = normalImage

    } else {

        print("Error: \(error)")

    }

}

```



#### While playing animation



If some frames are broken, the default image defined in APNG should be displayed as a fallback. You can get this in 

APNGKit for free. To get notified when this happens, listen to `APNGImageView.onFallBackToDefaultImage`:



```swift

imageView.onDecodingFrameError.delegate(on: self) { (self, error) in

    print("A frame cannot be decoded. After this, either onFallBackToDefaultImage or onFallBackToDefaultImageFailed happens.")

}



imageView.onFallBackToDefaultImage.delegate(on: self) { (self, _) in

    print("Fall back to default image.")

}

imageView.onFallBackToDefaultImageFailed.delegate(on: self) { (self, error) in

    print("Tried to fall back to default image, but it fails: \(error)")

}

```



### PNG compression



Xcode will compress all PNG files in your app bundle when you build the project. Since APNG is an extension format of 

PNG, Xcode will think there are redundancy data in that file and compress it into a single static image. When this happens,

you may inspect a log message from APNGKit:



> `CgBI` chunk found. It seems that the input image is compressed by Xcode and not supported by APNGKit. 

> Consider to rename it to `apng` to prevent compressing.



Usually this is not what you want when working with APNG. You can disable the PNG compression by setting 

"COMPRESS_PNG_FILES" to NO in the build settings of your app target. However, it will also prevent Xcode to optimize 

your other regular PNGs. 



A better approach would be renaming your APNG files with an extension besides of "png". If you do so, Xcode will stop 

recognizing your APNG files as PNG format, and will not apply compression on them. A suggested extension is "apng", 

which will be detected and handled by APNGKit seamlessly.



## Acknowledgement



The demo elephant image in README file is stolen from ICS Lab, you can find the original post [here](http://ics-web.jp/lab/archives/2441).



## Reference



If you are interested in APNG, you can know more about it from the links below (some of them are written in Chinese).



* [APNG Specification](https://wiki.mozilla.org/APNG_Specification)

* [APNG - Wikipedia](https://www.google.co.jp/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0CCkQFjABahUKEwjYxdSQjtrHAhWIn5QKHVDkAHs&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FAPNG&usg=AFQjCNF2CJ-OePHGKIhR14TdrCuEn9nn1A&sig2=188CAiDHZv0FVn7QVnhVVQ)

* [ε°η‰›ηŠŠ APNG εŠ›ζŒ«θ€ε€θ‘£ MNG](http://blog.wuxinan.net/archives/313)

* [ε†ε›žηœΈοΌŒδΈ½ε½±ε¦‚εˆ](http://isux.tencent.com/introduction-of-apng.html)



APNGKit can only load and display APNG image now. The creating feature will be developed later. If you need to create APNG file now, I suggest using [iSparta](http://isparta.github.io) or [apngasm](http://apngasm.sourceforge.net) instead for now.



## License



APNGKit is released under the MIT license. See LICENSE for details.