94 lines
3.5 KiB
Swift
94 lines
3.5 KiB
Swift
import CoreGraphics
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import Foundation
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import ImageIO
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import UniformTypeIdentifiers
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public enum JPEGTranscodeError: LocalizedError, Sendable {
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case decodeFailed
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case propertiesMissing
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case encodeFailed
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public var errorDescription: String? {
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switch self {
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case .decodeFailed:
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"Failed to decode image data"
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case .propertiesMissing:
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"Failed to read image properties"
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case .encodeFailed:
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"Failed to encode JPEG"
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}
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}
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}
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public struct JPEGTranscoder: Sendable {
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public static func clampQuality(_ quality: Double) -> Double {
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min(1.0, max(0.05, quality))
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}
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/// Re-encodes image data to JPEG, optionally downscaling so that the *oriented* pixel width is <= `maxWidthPx`.
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///
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/// - Important: This normalizes EXIF orientation (the output pixels are rotated if needed; orientation tag is not
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/// relied on).
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public static func transcodeToJPEG(
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imageData: Data,
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maxWidthPx: Int?,
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quality: Double) throws -> (data: Data, widthPx: Int, heightPx: Int)
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{
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guard let src = CGImageSourceCreateWithData(imageData as CFData, nil) else {
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throw JPEGTranscodeError.decodeFailed
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}
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guard
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let props = CGImageSourceCopyPropertiesAtIndex(src, 0, nil) as? [CFString: Any],
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let rawWidth = props[kCGImagePropertyPixelWidth] as? NSNumber,
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let rawHeight = props[kCGImagePropertyPixelHeight] as? NSNumber
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else {
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throw JPEGTranscodeError.propertiesMissing
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}
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let pixelWidth = rawWidth.intValue
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let pixelHeight = rawHeight.intValue
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let orientation = (props[kCGImagePropertyOrientation] as? NSNumber)?.intValue ?? 1
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guard pixelWidth > 0, pixelHeight > 0 else {
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throw JPEGTranscodeError.propertiesMissing
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}
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let rotates90 = orientation == 5 || orientation == 6 || orientation == 7 || orientation == 8
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let orientedWidth = rotates90 ? pixelHeight : pixelWidth
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let orientedHeight = rotates90 ? pixelWidth : pixelHeight
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let maxDim = max(orientedWidth, orientedHeight)
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let targetMaxPixelSize: Int = {
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guard let maxWidthPx, maxWidthPx > 0 else { return maxDim }
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guard orientedWidth > maxWidthPx else { return maxDim } // never upscale
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let scale = Double(maxWidthPx) / Double(orientedWidth)
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return max(1, Int((Double(maxDim) * scale).rounded(.toNearestOrAwayFromZero)))
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}()
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let thumbOpts: [CFString: Any] = [
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kCGImageSourceCreateThumbnailFromImageAlways: true,
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kCGImageSourceCreateThumbnailWithTransform: true,
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kCGImageSourceThumbnailMaxPixelSize: targetMaxPixelSize,
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kCGImageSourceShouldCacheImmediately: true,
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]
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guard let img = CGImageSourceCreateThumbnailAtIndex(src, 0, thumbOpts as CFDictionary) else {
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throw JPEGTranscodeError.decodeFailed
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}
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let out = NSMutableData()
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guard let dest = CGImageDestinationCreateWithData(out, UTType.jpeg.identifier as CFString, 1, nil) else {
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throw JPEGTranscodeError.encodeFailed
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}
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let q = self.clampQuality(quality)
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let encodeProps = [kCGImageDestinationLossyCompressionQuality: q] as CFDictionary
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CGImageDestinationAddImage(dest, img, encodeProps)
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guard CGImageDestinationFinalize(dest) else {
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throw JPEGTranscodeError.encodeFailed
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}
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return (out as Data, img.width, img.height)
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}
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}
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