77 lines
2.7 KiB
Swift
Executable File
77 lines
2.7 KiB
Swift
Executable File
import ImageIO
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import MobileCoreServices
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import UIKit
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typealias GIFProperties = [String : Double]
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let defaultDuration: Double = 0
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/// Retruns the duration of a frame at a specific index using an image source (an `CGImageSource` instance).
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///
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/// - returns: A frame duration.
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func CGImageSourceGIFFrameDuration(imageSource: CGImageSource, index: Int) -> NSTimeInterval {
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if !imageSource.isAnimatedGIF { return 0.0 }
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let duration = imageSource.GIFPropertiesAtIndex(index)
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>>- durationFromGIFProperties
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>>- capDuration
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return duration ?? defaultDuration
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}
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/// Ensures that a duration is never smaller than a threshold value.
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///
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/// - returns: A capped frame duration.
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func capDuration(duration: Double) -> Double? {
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if duration < 0 { return .None }
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let threshold = 0.02 - Double(FLT_EPSILON)
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let cappedDuration = duration < threshold ? 0.1 : duration
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return cappedDuration
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}
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/// Returns a frame duration from a `GIFProperties` dictionary.
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///
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/// - returns: A frame duration.
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func durationFromGIFProperties(properties: GIFProperties) -> Double? {
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guard let unclampedDelayTime = properties[String(kCGImagePropertyGIFUnclampedDelayTime)],
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let delayTime = properties[String(kCGImagePropertyGIFDelayTime)]
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else { return .None }
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return duration(unclampedDelayTime, delayTime: delayTime)
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}
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/// Calculates frame duration based on both clamped and unclamped times.
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///
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/// - returns: A frame duration.
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func duration(unclampedDelayTime: Double, delayTime: Double) -> Double {
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let delayArray = [unclampedDelayTime, delayTime]
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return delayArray.filter(isPositive).first ?? defaultDuration
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}
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/// Checks if a `Double` value is positive.
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///
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/// - returns: A boolean value that is `true` if the tested value is positive.
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func isPositive(value: Double) -> Bool {
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return value >= 0
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}
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/// An extension of `CGImageSourceRef` that add GIF introspection and easier property retrieval.
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extension CGImageSourceRef {
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/// Returns whether the image source contains an animated GIF.
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///
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/// - returns: A boolean value that is `true` if the image source contains animated GIF data.
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var isAnimatedGIF: Bool {
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let isTypeGIF = UTTypeConformsTo(CGImageSourceGetType(self) ?? "", kUTTypeGIF)
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let imageCount = CGImageSourceGetCount(self)
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return isTypeGIF != false && imageCount > 1
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}
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/// Returns the GIF properties at a specific index.
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///
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/// - parameter index: The index of the GIF properties to retrieve.
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/// - returns: A dictionary containing the GIF properties at the passed in index.
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func GIFPropertiesAtIndex(index: Int) -> GIFProperties? {
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let imageProperties = CGImageSourceCopyPropertiesAtIndex(self, index, nil) as Dictionary?
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return imageProperties?[String(kCGImagePropertyGIFDictionary)] as? GIFProperties
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}
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}
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