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package app.fedilab.android.mastodon.helper
import android.graphics.Bitmap
import android.graphics.Color
import kotlin.math.PI
import kotlin.math.cos
import kotlin.math.pow
import kotlin.math.withSign
class BlurHashDecoder {
fun decode(blurHash: String?, width: Int, height: Int, punch: Float = 1f): Bitmap? {
require(width > 0) { "Width must be greater than zero" }
require(height > 0) { "height must be greater than zero" }
if (blurHash == null || blurHash.length < 6) {
return null
}
val numCompEnc = decode83(blurHash, 0, 1)
val numCompX = (numCompEnc % 9) + 1
val numCompY = (numCompEnc / 9) + 1
if (blurHash.length != 4 + 2 * numCompX * numCompY) {
return null
}
val maxAcEnc = decode83(blurHash, 1, 2)
val maxAc = (maxAcEnc + 1) / 166f
val colors = Array(numCompX * numCompY) { i ->
if (i == 0) {
val colorEnc = decode83(blurHash, 2, 6)
decodeDc(colorEnc)
} else {
val from = 4 + i * 2
val colorEnc = decode83(blurHash, from, from + 2)
decodeAc(colorEnc, maxAc * punch)
}
}
return composeBitmap(width, height, numCompX, numCompY, colors)
}
private fun decode83(str: String, from: Int = 0, to: Int = str.length): Int {
var result = 0
for (i in from until to) {
val index = charMap[str[i]] ?: -1
if (index != -1) {
result = result * 83 + index
}
}
return result
}
private fun decodeDc(colorEnc: Int): FloatArray {
val r = colorEnc shr 16
val g = (colorEnc shr 8) and 255
val b = colorEnc and 255
return floatArrayOf(srgbToLinear(r), srgbToLinear(g), srgbToLinear(b))
}
private fun srgbToLinear(colorEnc: Int): Float {
val v = colorEnc / 255f
return if (v <= 0.04045f) {
(v / 12.92f)
} else {
((v + 0.055f) / 1.055f).pow(2.4f)
}
}
private fun decodeAc(value: Int, maxAc: Float): FloatArray {
val r = value / (19 * 19)
val g = (value / 19) % 19
val b = value % 19
return floatArrayOf(
signedPow2((r - 9) / 9.0f) * maxAc,
signedPow2((g - 9) / 9.0f) * maxAc,
signedPow2((b - 9) / 9.0f) * maxAc
)
}
private fun signedPow2(value: Float) = value.pow(2f).withSign(value)
private fun composeBitmap(
width: Int,
height: Int,
numCompX: Int,
numCompY: Int,
colors: Array<FloatArray>
): Bitmap {
val imageArray = IntArray(width * height)
for (y in 0 until height) {
for (x in 0 until width) {
var r = 0f
var g = 0f
var b = 0f
for (j in 0 until numCompY) {
for (i in 0 until numCompX) {
val basis = (cos(PI * x * i / width) * cos(PI * y * j / height)).toFloat()
val color = colors[j * numCompX + i]
r += color[0] * basis
g += color[1] * basis
b += color[2] * basis
}
}
imageArray[x + width * y] =
Color.rgb(linearToSrgb(r), linearToSrgb(g), linearToSrgb(b))
}
}
return Bitmap.createBitmap(imageArray, width, height, Bitmap.Config.ARGB_8888)
}
private fun linearToSrgb(value: Float): Int {
val v = value.coerceIn(0f, 1f)
return if (v <= 0.0031308f) {
(v * 12.92f * 255f + 0.5f).toInt()
} else {
((1.055f * v.pow(1 / 2.4f) - 0.055f) * 255 + 0.5f).toInt()
}
}
private val charMap = listOf(
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G',
'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '#', '$', '%', '*', '+', ',',
'-', '.', ':', ';', '=', '?', '@', '[', ']', '^', '_', '{', '|', '}', '~'
)
.mapIndexed { i, c -> c to i }
.toMap()
}
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