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import AppKit
import ArgumentParser
import Compute
import Metal
@main
struct PixelSort: ParsableCommand {
static let configuration = CommandConfiguration(
abstract: "GPU-accelerated pixel sorting for glitch art"
)
@Argument(help: "Input image path")
var input: String
@Argument(help: "Output image path")
var output: String
@Option(name: .shortAndLong, help: "Sort key: brightness, hue, saturation, red, green, blue")
var key: SortKeyOption = .brightness
@Option(name: .shortAndLong, help: "Lower brightness threshold (0.0–1.0)")
var lower: Float = 0.1
@Option(name: .shortAndLong, help: "Upper brightness threshold (0.0–1.0)")
var upper: Float = 0.9
@Flag(name: .shortAndLong, help: "Sort descending")
var descending: Bool = false
mutating func run() throws {
let device = MTLCreateSystemDefaultDevice()!
let compute = try Compute(device: device)
// Load image into a Metal texture
let inputURL = URL(fileURLWithPath: input)
let outputURL = URL(fileURLWithPath: self.output)
guard let nsImage = NSImage(contentsOf: inputURL),
let cgImage = nsImage.cgImage(forProposedRect: nil, context: nil, hints: nil)
else {
throw ValidationError("Could not load image at \(input)")
}
let width = cgImage.width
let height = cgImage.height
let desc = MTLTextureDescriptor.texture2DDescriptor(
pixelFormat: .rgba8Unorm,
width: width,
height: height,
mipmapped: false
)
desc.usage = [.shaderRead, .shaderWrite]
let texA = device.makeTexture(descriptor: desc)!
let texB = device.makeTexture(descriptor: desc)!
texA.label = "texA"
texB.label = "texB"
// Upload pixel data
let bytesPerPixel = 4
let bytesPerRow = bytesPerPixel * width
var pixelData = [UInt8](repeating: 0, count: width * height * bytesPerPixel)
let colorSpace = CGColorSpaceCreateDeviceRGB()
guard let ctx = CGContext(
data: &pixelData,
width: width,
height: height,
bitsPerComponent: 8,
bytesPerRow: bytesPerRow,
space: colorSpace,
bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue
) else {
throw ValidationError("Failed to create CGContext")
}
ctx.draw(cgImage, in: CGRect(x: 0, y: 0, width: width, height: height))
texA.replace(
region: MTLRegionMake2D(0, 0, width, height),
mipmapLevel: 0,
withBytes: pixelData,
bytesPerRow: bytesPerRow
)
// Load shaders
let shaderSource = try String(contentsOf: Bundle.module.url(forResource: "Shaders", withExtension: "metal")!, encoding: .utf8)
let library = ShaderLibrary.source(shaderSource)
var copyPipeline = try compute.makePipeline(function: library.copyTexture)
var sortPipeline = try compute.makePipeline(function: library.bitonicSortStep)
// Bitonic sort requires log2(nextPow2(width)) outer passes
let n = nextPowerOf2(width)
// Ping-pong between texA and texB
var readTex = texA
var writeTex = texB
var blockSize: Int = 2
while blockSize <= n {
var subBlockSize = blockSize
while subBlockSize >= 2 {
// Copy readTex → writeTex so untouched pixels carry forward
copyPipeline.arguments.src = .texture(readTex)
copyPipeline.arguments.dst = .texture(writeTex)
try compute.run(pipeline: copyPipeline, width: width, height: height)
// Run the bitonic compare-swap step
var params = BitonicParams(
width: UInt32(width),
height: UInt32(height),
blockSize: UInt32(blockSize),
subBlockSize: UInt32(subBlockSize),
sortKey: UInt32(key.metalValue),
lowerThreshold: lower,
upperThreshold: upper,
descending: descending ? 1 : 0
)
sortPipeline.arguments.inputTexture = .texture(readTex)
sortPipeline.arguments.outputTexture = .texture(writeTex)
let paramBuffer = device.makeBuffer(bytes: ¶ms, length: MemoryLayout<BitonicParams>.stride, options: .storageModeShared)!
sortPipeline.arguments.params = .buffer(paramBuffer)
try compute.run(pipeline: sortPipeline, width: width / 2, height: height)
// Swap
let tmp = readTex
readTex = writeTex
writeTex = tmp
subBlockSize /= 2
}
blockSize *= 2
}
// Read back from readTex (the last write destination after swap)
var outputData = [UInt8](repeating: 0, count: width * height * bytesPerPixel)
readTex.getBytes(
&outputData,
bytesPerRow: bytesPerRow,
from: MTLRegionMake2D(0, 0, width, height),
mipmapLevel: 0
)
// Save output
guard let outCtx = CGContext(
data: &outputData,
width: width,
height: height,
bitsPerComponent: 8,
bytesPerRow: bytesPerRow,
space: colorSpace,
bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue
),
let outCGImage = outCtx.makeImage()
else {
throw ValidationError("Failed to create output image")
}
let nsOutImage = NSBitmapImageRep(cgImage: outCGImage)
let ext = outputURL.pathExtension.lowercased()
let fileType: NSBitmapImageRep.FileType = ext == "jpg" || ext == "jpeg" ? .jpeg : .png
guard let data = nsOutImage.representation(using: fileType, properties: [:]) else {
throw ValidationError("Failed to encode output image")
}
try data.write(to: outputURL)
print("Pixel-sorted image saved to \(self.output) (\(width)×\(height))")
}
}
// MARK: - Helpers
struct BitonicParams {
var width: UInt32
var height: UInt32
var blockSize: UInt32
var subBlockSize: UInt32
var sortKey: UInt32
var lowerThreshold: Float
var upperThreshold: Float
var descending: UInt32
}
func nextPowerOf2(_ n: Int) -> Int {
var v = n - 1
v |= v >> 1
v |= v >> 2
v |= v >> 4
v |= v >> 8
v |= v >> 16
return v + 1
}
enum SortKeyOption: String, ExpressibleByArgument, CaseIterable {
case brightness, hue, saturation, red, green, blue
var metalValue: Int {
switch self {
case .brightness: return 0
case .hue: return 1
case .saturation: return 2
case .red: return 3
case .green: return 4
case .blue: return 5
}
}
}
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