refactor: Improve blurhash decoding performance (#770)
By Christophe Beyls in https://github.com/tuskyapp/Tusky/pull/4515. Their commit notes: Improve the performance of `BlurHashDecoder` while also reducing memory allocations. - Precompute cosines tables before composing the image so each cosine value is only computed once. - Compute cosines tables once if both are identical (for square images with the same number of colors in both dimensions). - Store colors in a one-dimension array instead of a two-dimension array to reduce memory allocations. - Use a simple String.indexOf() to find the index of a Base83 char, which is both faster and needs less memory than a HashMap thanks to better locality and no boxing of chars. - No cache is used, so computations may be performed in parallel on background threads without the need for synchronization which limits throughput.
This commit is contained in:
Nik Clayton
GitHub
parent
f3354d1aae
commit
33e1b418cf
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@ -19,6 +19,7 @@
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* Blurhash implementation from blurhash project:
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* https://github.com/woltapp/blurhash
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* Minor modifications by charlag
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* Major performance improvements by cbeyls
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*/
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package app.pachli.core.common.util
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@ -31,7 +32,6 @@ import kotlin.math.pow
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import kotlin.math.withSign
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object BlurHashDecoder {
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fun decode(blurHash: String?, width: Int, height: Int, punch: Float = 1f): Bitmap? {
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require(width > 0) { "Width must be greater than zero" }
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require(height > 0) { "height must be greater than zero" }
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@ -41,28 +41,27 @@ object BlurHashDecoder {
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val numCompEnc = decode83(blurHash, 0, 1)
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val numCompX = (numCompEnc % 9) + 1
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val numCompY = (numCompEnc / 9) + 1
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if (blurHash.length != 4 + 2 * numCompX * numCompY) {
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val totalComp = numCompX * numCompY
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if (blurHash.length != 4 + 2 * totalComp) {
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return null
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}
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val maxAcEnc = decode83(blurHash, 1, 2)
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val maxAc = (maxAcEnc + 1) / 166f
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val colors = Array(numCompX * numCompY) { i ->
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if (i == 0) {
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val colorEnc = decode83(blurHash, 2, 6)
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decodeDc(colorEnc)
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} else {
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val from = 4 + i * 2
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val colorEnc = decode83(blurHash, from, from + 2)
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decodeAc(colorEnc, maxAc * punch)
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}
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val colors = FloatArray(totalComp * 3)
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var colorEnc = decode83(blurHash, 2, 6)
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decodeDc(colorEnc, colors)
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for (i in 1 until totalComp) {
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val from = 4 + i * 2
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colorEnc = decode83(blurHash, from, from + 2)
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decodeAc(colorEnc, maxAc * punch, colors, i * 3)
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}
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return composeBitmap(width, height, numCompX, numCompY, colors)
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}
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private fun decode83(str: String, from: Int = 0, to: Int = str.length): Int {
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private fun decode83(str: String, from: Int, to: Int): Int {
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var result = 0
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for (i in from until to) {
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val index = charMap[str[i]] ?: -1
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val index = CHARS.indexOf(str[i])
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if (index != -1) {
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result = result * 83 + index
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}
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@ -70,11 +69,13 @@ object BlurHashDecoder {
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return result
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}
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private fun decodeDc(colorEnc: Int): FloatArray {
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val r = colorEnc shr 16
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val g = (colorEnc shr 8) and 255
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val b = colorEnc and 255
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return floatArrayOf(srgbToLinear(r), srgbToLinear(g), srgbToLinear(b))
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private fun decodeDc(colorEnc: Int, outArray: FloatArray) {
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val r = (colorEnc shr 16) and 0xFF
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val g = (colorEnc shr 8) and 0xFF
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val b = colorEnc and 0xFF
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outArray[0] = srgbToLinear(r)
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outArray[1] = srgbToLinear(g)
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outArray[2] = srgbToLinear(b)
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}
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private fun srgbToLinear(colorEnc: Int): Float {
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@ -86,15 +87,13 @@ object BlurHashDecoder {
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}
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}
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private fun decodeAc(value: Int, maxAc: Float): FloatArray {
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private fun decodeAc(value: Int, maxAc: Float, outArray: FloatArray, outIndex: Int) {
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val r = value / (19 * 19)
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val g = (value / 19) % 19
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val b = value % 19
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return floatArrayOf(
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signedPow2((r - 9) / 9.0f) * maxAc,
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signedPow2((g - 9) / 9.0f) * maxAc,
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signedPow2((b - 9) / 9.0f) * maxAc,
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)
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outArray[outIndex] = signedPow2((r - 9) / 9.0f) * maxAc
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outArray[outIndex + 1] = signedPow2((g - 9) / 9.0f) * maxAc
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outArray[outIndex + 2] = signedPow2((b - 9) / 9.0f) * maxAc
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}
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private fun signedPow2(value: Float) = value.pow(2f).withSign(value)
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@ -104,21 +103,29 @@ object BlurHashDecoder {
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height: Int,
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numCompX: Int,
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numCompY: Int,
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colors: Array<FloatArray>,
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colors: FloatArray,
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): Bitmap {
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val imageArray = IntArray(width * height)
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val cosinesX = createCosines(width, numCompX)
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val cosinesY = if (width == height && numCompX == numCompY) {
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cosinesX
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} else {
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createCosines(height, numCompY)
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}
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for (y in 0 until height) {
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for (x in 0 until width) {
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var r = 0f
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var g = 0f
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var b = 0f
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for (j in 0 until numCompY) {
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val cosY = cosinesY[y * numCompY + j]
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for (i in 0 until numCompX) {
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val basis = (cos(PI * x * i / width) * cos(PI * y * j / height)).toFloat()
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val color = colors[j * numCompX + i]
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r += color[0] * basis
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g += color[1] * basis
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b += color[2] * basis
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val cosX = cosinesX[x * numCompX + i]
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val basis = cosX * cosY
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val colorIndex = (j * numCompX + i) * 3
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r += colors[colorIndex] * basis
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g += colors[colorIndex + 1] * basis
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b += colors[colorIndex + 2] * basis
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}
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}
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imageArray[x + width * y] = Color.rgb(linearToSrgb(r), linearToSrgb(g), linearToSrgb(b))
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@ -127,6 +134,12 @@ object BlurHashDecoder {
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return Bitmap.createBitmap(imageArray, width, height, Bitmap.Config.ARGB_8888)
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}
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private fun createCosines(size: Int, numComp: Int) = FloatArray(size * numComp) { index ->
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val x = index / numComp
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val i = index % numComp
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cos(PI * x * i / size).toFloat()
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}
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private fun linearToSrgb(value: Float): Int {
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val v = value.coerceIn(0f, 1f)
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return if (v <= 0.0031308f) {
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@ -136,13 +149,5 @@ object BlurHashDecoder {
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}
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}
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private val charMap = listOf(
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'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G',
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'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
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'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
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'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '#', '$', '%', '*', '+', ',',
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'-', '.', ':', ';', '=', '?', '@', '[', ']', '^', '_', '{', '|', '}', '~',
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)
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.mapIndexed { i, c -> c to i }
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.toMap()
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private const val CHARS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~"
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}
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