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Improving performance of BlurHashDecode (Swift) #215

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Improving performance of BlurHashDecode (Swift) #215

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72 changes: 49 additions & 23 deletions Swift/BlurHashDecode.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -3,65 +3,91 @@ import UIKit
extension UIImage {
public convenience init?(blurHash: String, size: CGSize, punch: Float = 1) {
guard blurHash.count >= 6 else { return nil }

let sizeFlag = String(blurHash[0]).decode83()
let numY = (sizeFlag / 9) + 1
let numX = (sizeFlag % 9) + 1

let quantisedMaximumValue = String(blurHash[1]).decode83()
let sizeFlag = String(blurHash[0]).decode83()
let numY = (sizeFlag / 9) + 1
let numX = (sizeFlag % 9) + 1
let quantisedMaximumValue = String(blurHash[1]).decode83()
let maximumValue = Float(quantisedMaximumValue + 1) / 166

guard blurHash.count == 4 + 2 * numX * numY else { return nil }

let colours: [(Float, Float, Float)] = (0 ..< numX * numY).map { i in
if i == 0 {
let value = String(blurHash[2 ..< 6]).decode83()
let value = String(blurHash[2 ..< 6]).decode83()
return decodeDC(value)
} else {
let value = String(blurHash[4 + i * 2 ..< 4 + i * 2 + 2]).decode83()
return decodeAC(value, maximumValue: maximumValue * punch)
}
}

let width = Int(size.width)
let height = Int(size.height)
let bytesPerRow = width * 3
guard let data = CFDataCreateMutable(kCFAllocatorDefault, bytesPerRow * height) else { return nil }
CFDataSetLength(data, bytesPerRow * height)
guard let pixels = CFDataGetMutableBytePtr(data) else { return nil }

for y in 0 ..< height {
for x in 0 ..< width {

var y = 0

let floatWidth = Float(width)

let floatHeight = Float(height)

while y < height {
var x = 0

let floatY : Float = Float(y)

while x < width {
var j = 0

var r: Float = 0
var g: Float = 0
var b: Float = 0

for j in 0 ..< numY {
for i in 0 ..< numX {
let basis = cos(Float.pi * Float(x) * Float(i) / Float(width)) * cos(Float.pi * Float(y) * Float(j) / Float(height))

let floatX : Float = Float(x)

while j < numY {
var i = 0

let floatJ : Float = Float(j)

while i < numX {
let basis = cos(Float.pi * floatX * Float(i) / floatWidth) * cos(Float.pi * floatY * floatJ / floatHeight)
let colour = colours[i + j * numX]
r += colour.0 * basis
g += colour.1 * basis
b += colour.2 * basis

i += 1
}

j += 1
}

let intR = UInt8(linearTosRGB(r))
let intG = UInt8(linearTosRGB(g))
let intB = UInt8(linearTosRGB(b))

pixels[3 * x + 0 + y * bytesPerRow] = intR
pixels[3 * x + 1 + y * bytesPerRow] = intG
pixels[3 * x + 2 + y * bytesPerRow] = intB

x += 1
}

y += 1
}

let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue)

guard let provider = CGDataProvider(data: data) else { return nil }
guard let cgImage = CGImage(width: width, height: height, bitsPerComponent: 8, bitsPerPixel: 24, bytesPerRow: bytesPerRow,
space: CGColorSpaceCreateDeviceRGB(), bitmapInfo: bitmapInfo, provider: provider, decode: nil, shouldInterpolate: true, intent: .defaultIntent) else { return nil }

space: CGColorSpaceCreateDeviceRGB(), bitmapInfo: bitmapInfo, provider: provider, decode: nil, shouldInterpolate: true, intent: .defaultIntent) else { return nil }
self.init(cgImage: cgImage)
}
}
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