Hello,
I'm wondering if there is a way to programmatically write a series of UIImages into an APNG, similar to what the code below does for GIFs (credit: https://github.com/AFathi/ARVideoKit/tree/swift_5). I've tried implementing a similar solution but it doesn't seem to work. My code is included below
I've also done a lot of searching and have found lots of code for displaying APNGs, but have had no luck with code for writing them.
Any hints or pointers would be appreciated.
func generate(gif images: [UIImage], with delay: Float, loop count: Int = 0, _ finished: ((_ status: Bool, _ path: URL?) -> Void)? = nil) {
currentGIFPath = newGIFPath
gifQueue.async {
let gifSettings = [kCGImagePropertyGIFDictionary as String : [kCGImagePropertyGIFLoopCount as String : count]]
let imageSettings = [kCGImagePropertyGIFDictionary as String : [kCGImagePropertyGIFDelayTime as String : delay]]
guard let path = self.currentGIFPath else { return }
guard let destination = CGImageDestinationCreateWithURL(path as CFURL, __UTTypeGIF as! CFString, images.count, nil)
else { finished?(false, nil); return }
//logAR.message("\(destination)")
CGImageDestinationSetProperties(destination, gifSettings as CFDictionary)
for image in images {
if let imageRef = image.cgImage {
CGImageDestinationAddImage(destination, imageRef, imageSettings as CFDictionary)
}
}
if !CGImageDestinationFinalize(destination) {
finished?(false, nil); return
} else {
finished?(true, path)
}
}
}
My adaptation of the above code for APNGs (doesn't work; outputs empty file):
func generateAPNG(images: [UIImage], delay: Float, count: Int = 0) {
let apngSettings = [kCGImagePropertyPNGDictionary as String : [kCGImagePropertyAPNGLoopCount as String : count]]
let imageSettings = [kCGImagePropertyPNGDictionary as String : [kCGImagePropertyAPNGDelayTime as String : delay]]
guard let destination = CGImageDestinationCreateWithURL(outputURL as CFURL, UTType.png.identifier as CFString, images.count, nil)
else { fatalError("Failed") }
CGImageDestinationSetProperties(destination, apngSettings as CFDictionary)
for image in images {
if let imageRef = image.cgImage {
CGImageDestinationAddImage(destination, imageRef, imageSettings as CFDictionary)
}
}
}
Apple's documentation actually provides a Swift example of building a .apng that is quite old but still works just fine with a few modifications (I just tested it): https://developer.apple.com/library/archive/documentation/GraphicsImaging/Conceptual/ImageIOGuide/ikpg_dest/ikpg_dest.html
the second example (listing 3-3) is what you're interested in. The reference to kUTTypePNG, which is deprecated, can be updated to UTType.png.identifier as CFString. Otherwise, you'll need to actually write the code to provide the UIImages. There's also this mysterious line in their example let radians = M_PI * 2.0 * Double(i) / Double(frameCount) which doesn't do anything and can be removed. My guess is the author was going to use it to render a rotating image but didn't bother to actually implement it.
One other thing to note is that it seems like you may want to write the file with a ".png" extension even if it's an apng. I found instances where the ".apng" extension actually caused it to not work, but i'm not sure what the intended behavior is.