Gifu/Source/Classes/FrameStore.swift

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Swift
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import UIKit
import ImageIO
/// Responsible for storing and updating the frames of a single GIF.
class FrameStore {
/// Maximum duration to increment the frame timer with.
let maxTimeStep = 1.0
/// An array of animated frames from a single GIF image.
var animatedFrames = [AnimatedFrame]()
/// The target size for all frames.
let size: CGSize
/// The content mode to use when resizing.
let contentMode: UIViewContentMode
/// Maximum number of frames to load at once
let bufferFrameCount: Int
/// The total number of frames in the GIF.
var frameCount = 0
/// A reference to the original image source.
var imageSource: CGImageSource
/// The index of the current GIF frame.
var currentFrameIndex = 0 {
didSet {
previousFrameIndex = oldValue
}
}
/// The index of the previous GIF frame.
var previousFrameIndex = 0 {
didSet {
preloadFrameQueue.async {
self.updatePreloadedFrames()
}
}
}
/// Time elapsed since the last frame change. Used to determine when the frame should be updated.
var timeSinceLastFrameChange: TimeInterval = 0.0
/// Specifies whether GIF frames should be resized.
var shouldResizeFrames = true
/// Dispatch queue used for preloading images.
private lazy var preloadFrameQueue: DispatchQueue = {
return DispatchQueue(label: "co.kaishin.Gifu.preloadQueue")
}()
/// The current image frame to show.
var currentFrameImage: UIImage? {
return frame(at: currentFrameIndex)
}
/// The current frame duration
var currentFrameDuration: TimeInterval {
return duration(at: currentFrameIndex)
}
/// Is this image animatable?
var isAnimatable: Bool {
return imageSource.isAnimatedGIF
}
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/// Creates an animator instance from raw GIF image data and an `Animatable` delegate.
///
/// - parameter data: The raw GIF image data.
/// - parameter delegate: An `Animatable` delegate.
init(data: Data, size: CGSize, contentMode: UIViewContentMode, framePreloadCount: Int) {
let options = [String(kCGImageSourceShouldCache): kCFBooleanFalse] as CFDictionary
self.imageSource = CGImageSourceCreateWithData(data as CFData, options) ?? CGImageSourceCreateIncremental(options)
self.size = size
self.contentMode = contentMode
self.bufferFrameCount = framePreloadCount
}
// MARK: - Frames
/// Loads the frames from an image source, resizes them, then caches them in `animatedFrames`.
func prepareFrames(_ completionHandler: ((Void) -> Void)? = .none) {
frameCount = Int(CGImageSourceGetCount(imageSource))
animatedFrames.reserveCapacity(frameCount)
preloadFrameQueue.async {
self.setupAnimatedFrames()
if let handler = completionHandler { handler() }
}
}
/// Returns the frame at a particular index.
///
/// - parameter index: The index of the frame.
/// - returns: An optional image at a given frame.
func frame(at index: Int) -> UIImage? {
return animatedFrames[safe: index]?.image
}
/// Returns the duration at a particular index.
///
/// - parameter index: The index of the duration.
/// - returns: The duration of the given frame.
func duration(at index: Int) -> TimeInterval {
return animatedFrames[safe: index]?.duration ?? TimeInterval.infinity
}
/// Checks whether the frame should be changed and calls a handler with the results.
///
/// - parameter duration: A `CFTimeInterval` value that will be used to determine whether frame should be changed.
/// - parameter handler: A function that takes a `Bool` and returns nothing. It will be called with the frame change result.
func shouldChangeFrame(with duration: CFTimeInterval, handler: (Bool) -> Void) {
incrementTimeSinceLastFrameChange(with: duration)
if currentFrameDuration > timeSinceLastFrameChange {
handler(false)
} else {
resetTimeSinceLastFrameChange()
incrementCurrentFrameIndex()
handler(true)
}
}
}
private extension FrameStore {
/// Whether preloading is needed or not.
var preloadingIsNeeded: Bool {
return bufferFrameCount < frameCount - 1
}
/// Optionally loads a single frame from an image source, resizes it if required, then returns an `UIImage`.
///
/// - parameter index: The index of the frame to load.
/// - returns: An optional `UIImage` instance.
func loadFrame(at index: Int) -> UIImage? {
guard let imageRef = CGImageSourceCreateImageAtIndex(imageSource, index, nil) else { return .none }
let image = UIImage(cgImage: imageRef)
let scaledImage: UIImage?
if shouldResizeFrames {
switch self.contentMode {
case .scaleAspectFit: scaledImage = image.constrained(by: size)
case .scaleAspectFill: scaledImage = image.filling(size: size)
default: scaledImage = image.resized(to: size)
}
} else {
scaledImage = image
}
return scaledImage
}
/// Updates the frames by preloading new ones and replacing the previous frame with a placeholder.
func updatePreloadedFrames() {
if !preloadingIsNeeded { return }
animatedFrames[previousFrameIndex] = animatedFrames[previousFrameIndex].placeholderFrame
preloadIndexes(withStartingIndex: currentFrameIndex).forEach { index in
let currentAnimatedFrame = animatedFrames[index]
if !currentAnimatedFrame.isPlaceholder { return }
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animatedFrames[index] = currentAnimatedFrame.makeAnimatedFrame(with: loadFrame(at: index))
}
}
/// Increments the `timeSinceLastFrameChange` property with a given duration.
///
/// - parameter duration: An `NSTimeInterval` value to increment the `timeSinceLastFrameChange` property with.
func incrementTimeSinceLastFrameChange(with duration: TimeInterval) {
timeSinceLastFrameChange += min(maxTimeStep, duration)
}
/// Ensures that `timeSinceLastFrameChange` remains accurate after each frame change by substracting the `currentFrameDuration`.
func resetTimeSinceLastFrameChange() {
timeSinceLastFrameChange -= currentFrameDuration
}
/// Increments the `currentFrameIndex` property.
func incrementCurrentFrameIndex() {
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currentFrameIndex = increment(frameIndex: currentFrameIndex)
}
/// Increments a given frame index, taking into account the `frameCount` and looping when necessary.
///
/// - parameter index: The `Int` value to increment.
/// - parameter byValue: The `Int` value to increment with.
/// - returns: A new `Int` value.
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func increment(frameIndex: Int, by value: Int = 1) -> Int {
return (frameIndex + value) % frameCount
}
/// Returns the indexes of the frames to preload based on a starting frame index.
///
/// - parameter index: Starting index.
/// - returns: An array of indexes to preload.
func preloadIndexes(withStartingIndex index: Int) -> [Int] {
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let nextIndex = increment(frameIndex: index)
let lastIndex = increment(frameIndex: index, by: bufferFrameCount)
if lastIndex >= nextIndex {
return [Int](nextIndex...lastIndex)
} else {
return [Int](nextIndex..<frameCount) + [Int](0...lastIndex)
}
}
/// Set up animated frames after resetting them if necessary.
func setupAnimatedFrames() {
resetAnimatedFrames()
(0..<frameCount).forEach { index in
let frameDuration = CGImageFrameDuration(with: imageSource, atIndex: index)
animatedFrames += [AnimatedFrame(image: .none, duration: frameDuration)]
if index > bufferFrameCount { return }
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animatedFrames[index] = animatedFrames[index].makeAnimatedFrame(with: loadFrame(at: index))
}
}
/// Reset animated frames.
func resetAnimatedFrames() {
animatedFrames = []
}
}