letro-ios/ElementX/Sources/Other/BlurHashEncode.swift

/*
 Copyright (c) 2018 Wolt Enterprises
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in all
 copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */

// swiftlint:disable all

import UIKit

extension UIImage {
    public func blurHash(numberOfComponents components: (Int, Int)) -> String? {
        let pixelWidth = Int(round(size.width * scale))
        let pixelHeight = Int(round(size.height * scale))
        
        let context = CGContext(data: nil,
                                width: pixelWidth,
                                height: pixelHeight,
                                bitsPerComponent: 8,
                                bytesPerRow: pixelWidth * 4,
                                space: CGColorSpace(name: CGColorSpace.sRGB)!,
                                bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)!
        context.scaleBy(x: scale, y: -scale)
        context.translateBy(x: 0, y: -size.height)
        
        UIGraphicsPushContext(context)
        draw(at: .zero)
        UIGraphicsPopContext()
        
        guard let cgImage = context.makeImage(),
              let dataProvider = cgImage.dataProvider,
              let data = dataProvider.data,
              let pixels = CFDataGetBytePtr(data) else {
            assertionFailure("Unexpected error!")
            return nil
        }
        
        let width = cgImage.width
        let height = cgImage.height
        let bytesPerRow = cgImage.bytesPerRow
        
        var factors: [(Float, Float, Float)] = []
        for y in 0..<components.1 {
            for x in 0..<components.0 {
                let normalisation: Float = (x == 0 && y == 0) ? 1 : 2
                let factor = multiplyBasisFunction(pixels: pixels, width: width, height: height, bytesPerRow: bytesPerRow, bytesPerPixel: cgImage.bitsPerPixel / 8, pixelOffset: 0) {
                    normalisation * cos(Float.pi * Float(x) * $0 / Float(width)) as Float * cos(Float.pi * Float(y) * $1 / Float(height)) as Float
                }
                factors.append(factor)
            }
        }
        
        let dc = factors.first!
        let ac = factors.dropFirst()
        
        var hash = ""
        
        let sizeFlag = (components.0 - 1) + (components.1 - 1) * 9
        hash += sizeFlag.encode83(length: 1)
        
        let maximumValue: Float
        if ac.count > 0 {
            let actualMaximumValue = ac.map { max(abs($0.0), abs($0.1), abs($0.2)) }.max()!
            let quantisedMaximumValue = Int(max(0, min(82, floor(actualMaximumValue * 166 - 0.5))))
            maximumValue = Float(quantisedMaximumValue + 1) / 166
            hash += quantisedMaximumValue.encode83(length: 1)
        } else {
            maximumValue = 1
            hash += 0.encode83(length: 1)
        }
        
        hash += encodeDC(dc).encode83(length: 4)
        
        for factor in ac {
            hash += encodeAC(factor, maximumValue: maximumValue).encode83(length: 2)
        }
        
        return hash
    }
    
    private func multiplyBasisFunction(pixels: UnsafePointer<UInt8>, width: Int, height: Int, bytesPerRow: Int, bytesPerPixel: Int, pixelOffset: Int, basisFunction: (Float, Float) -> Float) -> (Float, Float, Float) {
        var r: Float = 0
        var g: Float = 0
        var b: Float = 0
        
        let buffer = UnsafeBufferPointer(start: pixels, count: height * bytesPerRow)
        
        for x in 0..<width {
            for y in 0..<height {
                let basis = basisFunction(Float(x), Float(y))
                r += basis * sRGBToLinear(buffer[bytesPerPixel * x + pixelOffset + 0 + y * bytesPerRow])
                g += basis * sRGBToLinear(buffer[bytesPerPixel * x + pixelOffset + 1 + y * bytesPerRow])
                b += basis * sRGBToLinear(buffer[bytesPerPixel * x + pixelOffset + 2 + y * bytesPerRow])
            }
        }
        
        let scale = 1 / Float(width * height)
        
        return (r * scale, g * scale, b * scale)
    }
}

private func encodeDC(_ value: (Float, Float, Float)) -> Int {
    let roundedR = linearTosRGB(value.0)
    let roundedG = linearTosRGB(value.1)
    let roundedB = linearTosRGB(value.2)
    return (roundedR << 16) + (roundedG << 8) + roundedB
}

private func encodeAC(_ value: (Float, Float, Float), maximumValue: Float) -> Int {
    let quantR = Int(max(0, min(18, floor(signPow(value.0 / maximumValue, 0.5) * 9 + 9.5))))
    let quantG = Int(max(0, min(18, floor(signPow(value.1 / maximumValue, 0.5) * 9 + 9.5))))
    let quantB = Int(max(0, min(18, floor(signPow(value.2 / maximumValue, 0.5) * 9 + 9.5))))
    
    return quantR * 19 * 19 + quantG * 19 + quantB
}

private func signPow(_ value: Float, _ exp: Float) -> Float {
    copysign(pow(abs(value), exp), value)
}

private func linearTosRGB(_ value: Float) -> Int {
    let v = max(0, min(1, value))
    if v <= 0.0031308 { return Int(v * 12.92 * 255 + 0.5) }
    else { return Int((1.055 * pow(v, 1 / 2.4) - 0.055) * 255 + 0.5) }
}

private func sRGBToLinear<Type: BinaryInteger>(_ value: Type) -> Float {
    let v = Float(Int64(value)) / 255
    if v <= 0.04045 { return v / 12.92 }
    else { return pow((v + 0.055) / 1.055, 2.4) }
}

private let encodeCharacters: [String] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~".map { String($0) }

extension BinaryInteger {
    func encode83(length: Int) -> String {
        var result = ""
        for i in 1...length {
            let digit = (Int(self) / pow(83, length - i)) % 83
            result += encodeCharacters[Int(digit)]
        }
        return result
    }
}

private func pow(_ base: Int, _ exponent: Int) -> Int {
    (0..<exponent).reduce(1) { value, _ in value * base }
}

// swiftlint:enable all