Gifu/Source/Animator.swift

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4.3 KiB
Swift
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import UIKit
import ImageIO
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/// Responsible for storing and updating the frames of a `AnimatableImageView` instance via delegation.
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class Animator {
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/// Maximum duration to increment the frame timer with.
let maxTimeStep = 1.0
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/// An array of animated frames from a single GIF image.
var animatedFrames = [AnimatedFrame]()
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/// The size to resize all frames to
let size: CGSize
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/// The content mode to use when resizing
let contentMode: UIViewContentMode
/// Maximum number of frames to load at once
let maxFrameCount: Int
/// The total number of frames in the GIF.
var frameCount = 0
/// A reference to the original image source.
var imageSource: CGImageSourceRef
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/// The index of the current GIF frame.
var currentFrameIndex = 0
/// The index of the current GIF frame from the source.
var currentPreloadIndex = 0
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/// Time elapsed since the last frame change. Used to determine when the frame should be updated.
var timeSinceLastFrameChange: NSTimeInterval = 0.0
/// Specifies whether GIF frames should be pre-scaled.
/// - seealso: `needsPrescaling` in AnimatableImageView.
var needsPrescaling = true
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/// The current image frame to show.
var currentFrame: UIImage? {
return frameAtIndex(currentFrameIndex)
}
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/// Is this image animatable?
var isAnimatable: Bool {
return imageSource.isAnimatedGIF
}
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/// Initializes an animator instance from raw GIF image data and an `Animatable` delegate.
///
/// - parameter data: The raw GIF image data.
/// - parameter delegate: An `Animatable` delegate.
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init(data: NSData, size: CGSize, contentMode: UIViewContentMode, framePreloadCount: Int) {
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let options = [String(kCGImageSourceShouldCache): kCFBooleanFalse]
self.imageSource = CGImageSourceCreateWithData(data, options) ?? CGImageSourceCreateIncremental(options)
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self.size = size
self.contentMode = contentMode
self.maxFrameCount = framePreloadCount
}
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// MARK: - Frames
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/// Loads the frames from an image source, resizes them, then caches them in `animatedFrames`.
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func prepareFrames() {
frameCount = Int(CGImageSourceGetCount(imageSource))
let framesToProcess = min(frameCount, maxFrameCount)
animatedFrames.reserveCapacity(framesToProcess)
animatedFrames = (0..<framesToProcess).reduce([]) { $0 + pure(prepareFrame($1)) }
currentPreloadIndex = framesToProcess
}
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/// Loads a single frame from an image source, resizes it, then returns an `AnimatedFrame`.
///
/// - parameter index: The index of the GIF image source to prepare
/// - returns: An AnimatedFrame object
func prepareFrame(index: Int) -> AnimatedFrame {
guard let frameImageRef = CGImageSourceCreateImageAtIndex(imageSource, index, nil) else {
return AnimatedFrame.null()
}
let frameDuration = CGImageSourceGIFFrameDuration(imageSource, index: index)
let image = UIImage(CGImage: frameImageRef)
let scaledImage: UIImage?
if needsPrescaling == true {
switch contentMode {
case .ScaleAspectFit: scaledImage = image.resizeAspectFit(size)
case .ScaleAspectFill: scaledImage = image.resizeAspectFill(size)
default: scaledImage = image.resize(size)
}
} else {
scaledImage = image
}
return AnimatedFrame(image: scaledImage, duration: frameDuration)
}
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/// Returns the frame at a particular index.
///
/// - parameter index: The index of the frame.
/// - returns: An optional image at a given frame.
func frameAtIndex(index: Int) -> UIImage? {
return animatedFrames[index].image
}
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/// Updates the current frame if necessary using the frame timer and the duration of each frame in `animatedFrames`.
///
/// - returns: An optional image at a given frame.
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func updateCurrentFrame(duration: CFTimeInterval) -> Bool {
timeSinceLastFrameChange += min(maxTimeStep, duration)
guard let frameDuration = animatedFrames[safe:currentFrameIndex]?.duration where
frameDuration <= timeSinceLastFrameChange else { return false }
timeSinceLastFrameChange -= frameDuration
let lastFrameIndex = currentFrameIndex
currentFrameIndex = ++currentFrameIndex % animatedFrames.count
// Loads the next needed frame for progressive loading
if animatedFrames.count < frameCount {
animatedFrames[lastFrameIndex] = prepareFrame(currentPreloadIndex)
currentPreloadIndex = ++currentPreloadIndex % frameCount
}
return true
}
}