127 lines
4.3 KiB
Kotlin
127 lines
4.3 KiB
Kotlin
package app.fedilab.android.mastodon.helper
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import android.graphics.Bitmap
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import android.graphics.Color
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import kotlin.math.PI
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import kotlin.math.cos
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import kotlin.math.pow
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import kotlin.math.withSign
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class 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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if (blurHash == null || blurHash.length < 6) {
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return null
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}
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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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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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}
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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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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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if (index != -1) {
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result = result * 83 + index
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}
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}
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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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}
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private fun srgbToLinear(colorEnc: Int): Float {
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val v = colorEnc / 255f
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return if (v <= 0.04045f) {
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(v / 12.92f)
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} else {
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((v + 0.055f) / 1.055f).pow(2.4f)
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}
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}
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private fun decodeAc(value: Int, maxAc: Float): FloatArray {
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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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}
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private fun signedPow2(value: Float) = value.pow(2f).withSign(value)
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private fun composeBitmap(
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width: Int,
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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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): Bitmap {
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val imageArray = IntArray(width * height)
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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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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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}
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}
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imageArray[x + width * y] =
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Color.rgb(linearToSrgb(r), linearToSrgb(g), linearToSrgb(b))
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}
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}
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return Bitmap.createBitmap(imageArray, width, height, Bitmap.Config.ARGB_8888)
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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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(v * 12.92f * 255f + 0.5f).toInt()
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} else {
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((1.055f * v.pow(1 / 2.4f) - 0.055f) * 255 + 0.5f).toInt()
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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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} |