texturedspenc.c 23.5 KB
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/*
 * Texture block compression
 * Copyright (C) 2015 Vittorio Giovara <vittorio.giovara@gmail.com>
 * Based on public domain code by Fabian Giesen, Sean Barrett and Yann Collet.
 *
 * This file is part of Libav
 *
 * 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.
 */

#include <stddef.h>
#include <stdint.h>

#include "libavutil/attributes.h"
#include "libavutil/common.h"
#include "libavutil/intreadwrite.h"

#include "texturedsp.h"

const static uint8_t expand5[32] = {
      0,   8,  16,  24,  33,  41,  49,  57,  66,  74,  82,  90,
     99, 107, 115, 123, 132, 140, 148, 156, 165, 173, 181, 189,
    198, 206, 214, 222, 231, 239, 247, 255,
};

const static uint8_t expand6[64] = {
      0,   4,   8,  12,  16,  20,  24,  28,  32,  36,  40,  44,
     48,  52,  56,  60,  65,  69,  73,  77,  81,  85,  89,  93,
     97, 101, 105, 109, 113, 117, 121, 125, 130, 134, 138, 142,
    146, 150, 154, 158, 162, 166, 170, 174, 178, 182, 186, 190,
    195, 199, 203, 207, 211, 215, 219, 223, 227, 231, 235, 239,
    243, 247, 251, 255,
};

const static uint8_t match5[256][2] = {
    {  0,  0 }, {  0,  0 }, {  0,  1 }, {  0,  1 }, {  1,  0 }, {  1,  0 },
    {  1,  0 }, {  1,  1 }, {  1,  1 }, {  2,  0 }, {  2,  0 }, {  0,  4 },
    {  2,  1 }, {  2,  1 }, {  2,  1 }, {  3,  0 }, {  3,  0 }, {  3,  0 },
    {  3,  1 }, {  1,  5 }, {  3,  2 }, {  3,  2 }, {  4,  0 }, {  4,  0 },
    {  4,  1 }, {  4,  1 }, {  4,  2 }, {  4,  2 }, {  4,  2 }, {  3,  5 },
    {  5,  1 }, {  5,  1 }, {  5,  2 }, {  4,  4 }, {  5,  3 }, {  5,  3 },
    {  5,  3 }, {  6,  2 }, {  6,  2 }, {  6,  2 }, {  6,  3 }, {  5,  5 },
    {  6,  4 }, {  6,  4 }, {  4,  8 }, {  7,  3 }, {  7,  3 }, {  7,  3 },
    {  7,  4 }, {  7,  4 }, {  7,  4 }, {  7,  5 }, {  5,  9 }, {  7,  6 },
    {  7,  6 }, {  8,  4 }, {  8,  4 }, {  8,  5 }, {  8,  5 }, {  8,  6 },
    {  8,  6 }, {  8,  6 }, {  7,  9 }, {  9,  5 }, {  9,  5 }, {  9,  6 },
    {  8,  8 }, {  9,  7 }, {  9,  7 }, {  9,  7 }, { 10,  6 }, { 10,  6 },
    { 10,  6 }, { 10,  7 }, {  9,  9 }, { 10,  8 }, { 10,  8 }, {  8, 12 },
    { 11,  7 }, { 11,  7 }, { 11,  7 }, { 11,  8 }, { 11,  8 }, { 11,  8 },
    { 11,  9 }, {  9, 13 }, { 11, 10 }, { 11, 10 }, { 12,  8 }, { 12,  8 },
    { 12,  9 }, { 12,  9 }, { 12, 10 }, { 12, 10 }, { 12, 10 }, { 11, 13 },
    { 13,  9 }, { 13,  9 }, { 13, 10 }, { 12, 12 }, { 13, 11 }, { 13, 11 },
    { 13, 11 }, { 14, 10 }, { 14, 10 }, { 14, 10 }, { 14, 11 }, { 13, 13 },
    { 14, 12 }, { 14, 12 }, { 12, 16 }, { 15, 11 }, { 15, 11 }, { 15, 11 },
    { 15, 12 }, { 15, 12 }, { 15, 12 }, { 15, 13 }, { 13, 17 }, { 15, 14 },
    { 15, 14 }, { 16, 12 }, { 16, 12 }, { 16, 13 }, { 16, 13 }, { 16, 14 },
    { 16, 14 }, { 16, 14 }, { 15, 17 }, { 17, 13 }, { 17, 13 }, { 17, 14 },
    { 16, 16 }, { 17, 15 }, { 17, 15 }, { 17, 15 }, { 18, 14 }, { 18, 14 },
    { 18, 14 }, { 18, 15 }, { 17, 17 }, { 18, 16 }, { 18, 16 }, { 16, 20 },
    { 19, 15 }, { 19, 15 }, { 19, 15 }, { 19, 16 }, { 19, 16 }, { 19, 16 },
    { 19, 17 }, { 17, 21 }, { 19, 18 }, { 19, 18 }, { 20, 16 }, { 20, 16 },
    { 20, 17 }, { 20, 17 }, { 20, 18 }, { 20, 18 }, { 20, 18 }, { 19, 21 },
    { 21, 17 }, { 21, 17 }, { 21, 18 }, { 20, 20 }, { 21, 19 }, { 21, 19 },
    { 21, 19 }, { 22, 18 }, { 22, 18 }, { 22, 18 }, { 22, 19 }, { 21, 21 },
    { 22, 20 }, { 22, 20 }, { 20, 24 }, { 23, 19 }, { 23, 19 }, { 23, 19 },
    { 23, 20 }, { 23, 20 }, { 23, 20 }, { 23, 21 }, { 21, 25 }, { 23, 22 },
    { 23, 22 }, { 24, 20 }, { 24, 20 }, { 24, 21 }, { 24, 21 }, { 24, 22 },
    { 24, 22 }, { 24, 22 }, { 23, 25 }, { 25, 21 }, { 25, 21 }, { 25, 22 },
    { 24, 24 }, { 25, 23 }, { 25, 23 }, { 25, 23 }, { 26, 22 }, { 26, 22 },
    { 26, 22 }, { 26, 23 }, { 25, 25 }, { 26, 24 }, { 26, 24 }, { 24, 28 },
    { 27, 23 }, { 27, 23 }, { 27, 23 }, { 27, 24 }, { 27, 24 }, { 27, 24 },
    { 27, 25 }, { 25, 29 }, { 27, 26 }, { 27, 26 }, { 28, 24 }, { 28, 24 },
    { 28, 25 }, { 28, 25 }, { 28, 26 }, { 28, 26 }, { 28, 26 }, { 27, 29 },
    { 29, 25 }, { 29, 25 }, { 29, 26 }, { 28, 28 }, { 29, 27 }, { 29, 27 },
    { 29, 27 }, { 30, 26 }, { 30, 26 }, { 30, 26 }, { 30, 27 }, { 29, 29 },
    { 30, 28 }, { 30, 28 }, { 30, 28 }, { 31, 27 }, { 31, 27 }, { 31, 27 },
    { 31, 28 }, { 31, 28 }, { 31, 28 }, { 31, 29 }, { 31, 29 }, { 31, 30 },
    { 31, 30 }, { 31, 30 }, { 31, 31 }, { 31, 31 },
};

const static uint8_t match6[256][2] = {
    {  0,  0 }, {  0,  1 }, {  1,  0 }, {  1,  0 }, {  1,  1 }, {  2,  0 },
    {  2,  1 }, {  3,  0 }, {  3,  0 }, {  3,  1 }, {  4,  0 }, {  4,  0 },
    {  4,  1 }, {  5,  0 }, {  5,  1 }, {  6,  0 }, {  6,  0 }, {  6,  1 },
    {  7,  0 }, {  7,  0 }, {  7,  1 }, {  8,  0 }, {  8,  1 }, {  8,  1 },
    {  8,  2 }, {  9,  1 }, {  9,  2 }, {  9,  2 }, {  9,  3 }, { 10,  2 },
    { 10,  3 }, { 10,  3 }, { 10,  4 }, { 11,  3 }, { 11,  4 }, { 11,  4 },
    { 11,  5 }, { 12,  4 }, { 12,  5 }, { 12,  5 }, { 12,  6 }, { 13,  5 },
    { 13,  6 }, {  8, 16 }, { 13,  7 }, { 14,  6 }, { 14,  7 }, {  9, 17 },
    { 14,  8 }, { 15,  7 }, { 15,  8 }, { 11, 16 }, { 15,  9 }, { 15, 10 },
    { 16,  8 }, { 16,  9 }, { 16, 10 }, { 15, 13 }, { 17,  9 }, { 17, 10 },
    { 17, 11 }, { 15, 16 }, { 18, 10 }, { 18, 11 }, { 18, 12 }, { 16, 16 },
    { 19, 11 }, { 19, 12 }, { 19, 13 }, { 17, 17 }, { 20, 12 }, { 20, 13 },
    { 20, 14 }, { 19, 16 }, { 21, 13 }, { 21, 14 }, { 21, 15 }, { 20, 17 },
    { 22, 14 }, { 22, 15 }, { 25, 10 }, { 22, 16 }, { 23, 15 }, { 23, 16 },
    { 26, 11 }, { 23, 17 }, { 24, 16 }, { 24, 17 }, { 27, 12 }, { 24, 18 },
    { 25, 17 }, { 25, 18 }, { 28, 13 }, { 25, 19 }, { 26, 18 }, { 26, 19 },
    { 29, 14 }, { 26, 20 }, { 27, 19 }, { 27, 20 }, { 30, 15 }, { 27, 21 },
    { 28, 20 }, { 28, 21 }, { 28, 21 }, { 28, 22 }, { 29, 21 }, { 29, 22 },
    { 24, 32 }, { 29, 23 }, { 30, 22 }, { 30, 23 }, { 25, 33 }, { 30, 24 },
    { 31, 23 }, { 31, 24 }, { 27, 32 }, { 31, 25 }, { 31, 26 }, { 32, 24 },
    { 32, 25 }, { 32, 26 }, { 31, 29 }, { 33, 25 }, { 33, 26 }, { 33, 27 },
    { 31, 32 }, { 34, 26 }, { 34, 27 }, { 34, 28 }, { 32, 32 }, { 35, 27 },
    { 35, 28 }, { 35, 29 }, { 33, 33 }, { 36, 28 }, { 36, 29 }, { 36, 30 },
    { 35, 32 }, { 37, 29 }, { 37, 30 }, { 37, 31 }, { 36, 33 }, { 38, 30 },
    { 38, 31 }, { 41, 26 }, { 38, 32 }, { 39, 31 }, { 39, 32 }, { 42, 27 },
    { 39, 33 }, { 40, 32 }, { 40, 33 }, { 43, 28 }, { 40, 34 }, { 41, 33 },
    { 41, 34 }, { 44, 29 }, { 41, 35 }, { 42, 34 }, { 42, 35 }, { 45, 30 },
    { 42, 36 }, { 43, 35 }, { 43, 36 }, { 46, 31 }, { 43, 37 }, { 44, 36 },
    { 44, 37 }, { 44, 37 }, { 44, 38 }, { 45, 37 }, { 45, 38 }, { 40, 48 },
    { 45, 39 }, { 46, 38 }, { 46, 39 }, { 41, 49 }, { 46, 40 }, { 47, 39 },
    { 47, 40 }, { 43, 48 }, { 47, 41 }, { 47, 42 }, { 48, 40 }, { 48, 41 },
    { 48, 42 }, { 47, 45 }, { 49, 41 }, { 49, 42 }, { 49, 43 }, { 47, 48 },
    { 50, 42 }, { 50, 43 }, { 50, 44 }, { 48, 48 }, { 51, 43 }, { 51, 44 },
    { 51, 45 }, { 49, 49 }, { 52, 44 }, { 52, 45 }, { 52, 46 }, { 51, 48 },
    { 53, 45 }, { 53, 46 }, { 53, 47 }, { 52, 49 }, { 54, 46 }, { 54, 47 },
    { 57, 42 }, { 54, 48 }, { 55, 47 }, { 55, 48 }, { 58, 43 }, { 55, 49 },
    { 56, 48 }, { 56, 49 }, { 59, 44 }, { 56, 50 }, { 57, 49 }, { 57, 50 },
    { 60, 45 }, { 57, 51 }, { 58, 50 }, { 58, 51 }, { 61, 46 }, { 58, 52 },
    { 59, 51 }, { 59, 52 }, { 62, 47 }, { 59, 53 }, { 60, 52 }, { 60, 53 },
    { 60, 53 }, { 60, 54 }, { 61, 53 }, { 61, 54 }, { 61, 54 }, { 61, 55 },
    { 62, 54 }, { 62, 55 }, { 62, 55 }, { 62, 56 }, { 63, 55 }, { 63, 56 },
    { 63, 56 }, { 63, 57 }, { 63, 58 }, { 63, 59 }, { 63, 59 }, { 63, 60 },
    { 63, 61 }, { 63, 62 }, { 63, 62 }, { 63, 63 },
};

/* Multiplication over 8 bit emulation */
#define mul8(a, b) (a * b + 128 + ((a * b + 128) >> 8)) >> 8

/* Conversion from rgb24 to rgb565 */
#define rgb2rgb565(r, g, b) \
    (mul8(r, 31) << 11) | (mul8(g, 63) << 5) | (mul8(b, 31) << 0)

/* Linear interpolation at 1/3 point between a and b */
#define lerp13(a, b) (2 * a + b) / 3

/* Linear interpolation on an RGB pixel */
static inline void lerp13rgb(uint8_t *out, uint8_t *p1, uint8_t *p2)
{
    out[0] = lerp13(p1[0], p2[0]);
    out[1] = lerp13(p1[1], p2[1]);
    out[2] = lerp13(p1[2], p2[2]);
}

/* Conversion from rgb565 to rgb24 */
static inline void rgb5652rgb(uint8_t *out, uint16_t v)
{
    int rv = (v & 0xf800) >> 11;
    int gv = (v & 0x07e0) >> 5;
    int bv = (v & 0x001f) >> 0;

    out[0] = expand5[rv];
    out[1] = expand6[gv];
    out[2] = expand5[bv];
    out[3] = 0;
}

/* Color matching function */
static unsigned int match_colors(const uint8_t *block, ptrdiff_t stride,
                                 uint16_t c0, uint16_t c1)
{
    uint32_t mask = 0;
    int dirr, dirg, dirb;
    int dots[16];
    int stops[4];
    int x, y, k = 0;
    int c0_point, half_point, c3_point;
    uint8_t color[16];
    const int indexMap[8] = {
        0 << 30, 2 << 30, 0 << 30, 2 << 30,
        3 << 30, 3 << 30, 1 << 30, 1 << 30,
    };

    /* Fill color and compute direction for each component */
    rgb5652rgb(color + 0, c0);
    rgb5652rgb(color + 4, c1);
    lerp13rgb(color + 8, color + 0, color + 4);
    lerp13rgb(color + 12, color + 4, color + 0);

    dirr = color[0 * 4 + 0] - color[1 * 4 + 0];
    dirg = color[0 * 4 + 1] - color[1 * 4 + 1];
    dirb = color[0 * 4 + 2] - color[1 * 4 + 2];

    for (y = 0; y < 4; y++) {
        for (x = 0; x < 4; x++)
            dots[k++] = block[0 + x * 4 + y * stride] * dirr +
                        block[1 + x * 4 + y * stride] * dirg +
                        block[2 + x * 4 + y * stride] * dirb;

        stops[y] = color[0 + y * 4] * dirr +
                   color[1 + y * 4] * dirg +
                   color[2 + y * 4] * dirb;
    }

    /* Think of the colors as arranged on a line; project point onto that line,
     * then choose next color out of available ones. we compute the crossover
     * points for 'best color in top half'/'best in bottom half' and then
     * the same inside that subinterval.
     *
     * Relying on this 1d approximation isn't always optimal in terms of
     * euclidean distance, but it's very close and a lot faster.
     *
     * http://cbloomrants.blogspot.com/2008/12/12-08-08-dxtc-summary.html */
    c0_point   = (stops[1] + stops[3]) >> 1;
    half_point = (stops[3] + stops[2]) >> 1;
    c3_point   = (stops[2] + stops[0]) >> 1;

    for (x = 0; x < 16; x++) {
        int dot  = dots[x];
        int bits = (dot < half_point ? 4 : 0) |
                   (dot < c0_point   ? 2 : 0) |
                   (dot < c3_point   ? 1 : 0);

        mask >>= 2;
        mask  |= indexMap[bits];
    }

    return mask;
}

/* Color optimization function */
static void optimize_colors(const uint8_t *block, ptrdiff_t stride,
                            uint16_t *pmax16, uint16_t *pmin16)
{
    const uint8_t *minp;
    const uint8_t *maxp;
    const int iter_power = 4;
    double magn;
    int v_r, v_g, v_b;
    float covf[6], vfr, vfg, vfb;
    int mind, maxd;
    int cov[6] = { 0 };
    int mu[3], min[3], max[3];
    int ch, iter, x, y;

    /* Determine color distribution */
    for (ch = 0; ch < 3; ch++) {
        const uint8_t *bp = &block[ch];
        int muv, minv, maxv;

        muv = minv = maxv = bp[0];
        for (y = 0; y < 4; y++) {
            for (x = 4; x < 4; x += 4) {
                muv += bp[x * 4 + y * stride];
                if (bp[x] < minv)
                    minv = bp[x * 4 + y * stride];
                else if (bp[x] > maxv)
                    maxv = bp[x * 4 + y * stride];
            }
        }

        mu[ch]  = (muv + 8) >> 4;
        min[ch] = minv;
        max[ch] = maxv;
    }

    /* Determine covariance matrix */
    for (y = 0; y < 4; y++) {
        for (x = 0; x < 4; x++) {
            int r = block[x * 4 + stride * y + 0] - mu[0];
            int g = block[x * 4 + stride * y + 1] - mu[1];
            int b = block[x * 4 + stride * y + 2] - mu[2];

            cov[0] += r * r;
            cov[1] += r * g;
            cov[2] += r * b;
            cov[3] += g * g;
            cov[4] += g * b;
            cov[5] += b * b;
        }
    }

    /* Convert covariance matrix to float, find principal axis via power iter */
    for (x = 0; x < 6; x++)
        covf[x] = cov[x] / 255.0f;

    vfr = (float) (max[0] - min[0]);
    vfg = (float) (max[1] - min[1]);
    vfb = (float) (max[2] - min[2]);

    for (iter = 0; iter < iter_power; iter++) {
        float r = vfr * covf[0] + vfg * covf[1] + vfb * covf[2];
        float g = vfr * covf[1] + vfg * covf[3] + vfb * covf[4];
        float b = vfr * covf[2] + vfg * covf[4] + vfb * covf[5];

        vfr = r;
        vfg = g;
        vfb = b;
    }

    magn = fabs(vfr);
    if (fabs(vfg) > magn)
        magn = fabs(vfg);
    if (fabs(vfb) > magn)
        magn = fabs(vfb);

    /* if magnitudo is too small, default to luminance */
    if (magn < 4.0f) {
        /* JPEG YCbCr luma coefs, scaled by 1000 */
        v_r = 299;
        v_g = 587;
        v_b = 114;
    } else {
        magn = 512.0 / magn;
        v_r  = (int) (vfr * magn);
        v_g  = (int) (vfg * magn);
        v_b  = (int) (vfb * magn);
    }

    /* Pick colors at extreme points */
    mind = maxd = block[0] * v_r + block[1] * v_g + block[2] * v_b;
    minp = maxp = block;
    for (y = 0; y < 4; y++) {
        for (x = 0; x < 4; x++) {
            int dot = block[x * 4 + y * stride + 0] * v_r +
                      block[x * 4 + y * stride + 1] * v_g +
                      block[x * 4 + y * stride + 2] * v_b;

            if (dot < mind) {
                mind = dot;
                minp = block + x * 4 + y * stride;
            } else if (dot > maxd) {
                maxd = dot;
                maxp = block + x * 4 + y * stride;
            }
        }
    }

    *pmax16 = rgb2rgb565(maxp[0], maxp[1], maxp[2]);
    *pmin16 = rgb2rgb565(minp[0], minp[1], minp[2]);
}

/* Try to optimize colors to suit block contents better, by solving
 * a least squares system via normal equations + Cramer's rule. */
static int refine_colors(const uint8_t *block, ptrdiff_t stride,
                         uint16_t *pmax16, uint16_t *pmin16, uint32_t mask)
{
    uint32_t cm = mask;
    uint16_t oldMin = *pmin16;
    uint16_t oldMax = *pmax16;
    uint16_t min16, max16;
    int x, y;

    /* Additional magic to save a lot of multiplies in the accumulating loop.
     * The tables contain precomputed products of weights for least squares
     * system, accumulated inside one 32-bit register */
    const int w1tab[4] = { 3, 0, 2, 1 };
    const int prods[4] = { 0x090000, 0x000900, 0x040102, 0x010402 };

    /* Check if all pixels have the same index */
366
    if ((mask ^ (mask << 2)) < 4) {
367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659
        /* If so, linear system would be singular; solve using optimal
         * single-color match on average color. */
        int r = 8, g = 8, b = 8;
        for (y = 0; y < 4; y++) {
            for (x = 0; x < 4; x++) {
                r += block[0 + x * 4 + y * stride];
                g += block[1 + x * 4 + y * stride];
                b += block[2 + x * 4 + y * stride];
            }
        }

        r >>= 4;
        g >>= 4;
        b >>= 4;

        max16 = (match5[r][0] << 11) | (match6[g][0] << 5) | match5[b][0];
        min16 = (match5[r][1] << 11) | (match6[g][1] << 5) | match5[b][1];
    } else {
        float fr, fg, fb;
        int at1_r = 0, at1_g = 0, at1_b = 0;
        int at2_r = 0, at2_g = 0, at2_b = 0;
        int akku = 0;
        int xx, xy, yy;

        for (y = 0; y < 4; y++) {
            for (x = 0; x < 4; x++) {
                int step = cm & 3;
                int w1 = w1tab[step];
                int r = block[0 + x * 4 + y * stride];
                int g = block[1 + x * 4 + y * stride];
                int b = block[2 + x * 4 + y * stride];

                akku  += prods[step];
                at1_r += w1 * r;
                at1_g += w1 * g;
                at1_b += w1 * b;
                at2_r += r;
                at2_g += g;
                at2_b += b;

                cm >>= 2;
            }
        }

        at2_r = 3 * at2_r - at1_r;
        at2_g = 3 * at2_g - at1_g;
        at2_b = 3 * at2_b - at1_b;

        /* Extract solutions and decide solvability */
        xx =  akku >> 16;
        yy = (akku >>  8) & 0xFF;
        xy = (akku >>  0) & 0xFF;

        fr = 3.0f * 31.0f / 255.0f / (xx * yy - xy * xy);
        fg = fr * 63.0f / 31.0f;
        fb = fr;

        /* Solve */
        max16  = av_clip_uintp2((at1_r * yy - at2_r * xy) * fr + 0.5f, 5) << 11;
        max16 |= av_clip_uintp2((at1_g * yy - at2_g * xy) * fg + 0.5f, 6) <<  5;
        max16 |= av_clip_uintp2((at1_b * yy - at2_b * xy) * fb + 0.5f, 5) <<  0;

        min16  = av_clip_uintp2((at2_r * xx - at1_r * xy) * fr + 0.5f, 5) << 11;
        min16 |= av_clip_uintp2((at2_g * xx - at1_g * xy) * fg + 0.5f, 6) <<  5;
        min16 |= av_clip_uintp2((at2_b * xx - at1_b * xy) * fb + 0.5f, 5) <<  0;
    }

    *pmin16 = min16;
    *pmax16 = max16;
    return oldMin != min16 || oldMax != max16;
}

/* Check if input block is a constant color */
static int constant_color(const uint8_t *block, ptrdiff_t stride)
{
    int x, y;
    uint32_t first = AV_RL32(block);

    for (y = 0; y < 4; y++)
        for (x = 0; x < 4; x++)
            if (first != AV_RL32(block + x * 4 + y * stride))
                return 0;
    return 1;
}

/* Main color compression function */
static void compress_color(uint8_t *dst, ptrdiff_t stride, const uint8_t *block)
{
    uint32_t mask;
    uint16_t max16, min16;
    int constant = constant_color(block, stride);

    /* Constant color will load values from tables */
    if (constant) {
        int r = block[0];
        int g = block[1];
        int b = block[2];
        mask  = 0xAAAAAAAA;
        max16 = (match5[r][0] << 11) | (match6[g][0] << 5) | match5[b][0];
        min16 = (match5[r][1] << 11) | (match6[g][1] << 5) | match5[b][1];
    } else {
        int refine;

        /* Otherwise find pca and map along principal axis */
        optimize_colors(block, stride, &max16, &min16);
        if (max16 != min16)
            mask = match_colors(block, stride, max16, min16);
        else
            mask = 0;

        /* One pass refinement */
        refine  = refine_colors(block, stride, &max16, &min16, mask);
        if (refine) {
            if (max16 != min16)
                mask = match_colors(block, stride, max16, min16);
            else
                mask = 0;
        }
    }

    /* Finally write the color block */
    if (max16 < min16) {
        FFSWAP(uint16_t, min16, max16);
        mask ^= 0x55555555;
    }

    AV_WL16(dst + 0, max16);
    AV_WL16(dst + 2, min16);
    AV_WL32(dst + 4, mask);
}

/* Alpha compression function */
static void compress_alpha(uint8_t *dst, ptrdiff_t stride, const uint8_t *block)
{
    int x, y;
    int dist, bias, dist4, dist2;
    int mn, mx;
    int bits = 0;
    int mask = 0;

    memset(dst, 0, 8);

    /* Find min/max color */
    mn = mx = block[3];
    for (y = 0; y < 4; y++) {
        for (x = 0; x < 4; x++) {
            int val = block[3 + x * 4 + y * stride];
            if (val < mn)
                mn = val;
            else if (val > mx)
                mx = val;
        }
    }

    /* Encode them */
    dst[0] = (uint8_t) mx;
    dst[1] = (uint8_t) mn;
    dst += 2;

    /* Mono-alpha shortcut */
    if (mn == mx)
        return;

    /* Determine bias and emit color indices.
     * Given the choice of mx/mn, these indices are optimal:
     * fgiesen.wordpress.com/2009/12/15/dxt5-alpha-block-index-determination */
    dist = mx - mn;

    dist4 = dist * 4;
    dist2 = dist * 2;
    if (dist < 8)
        bias = dist - 1 - mn * 7;
    else
        bias = dist / 2 + 2 - mn * 7;

    for (y = 0; y < 4; y++) {
        for (x = 0; x < 4; x++) {
            int alp = block[3 + x * 4 + y * stride] * 7 + bias;
            int ind, tmp;

            /* This is a "linear scale" lerp factor between 0 (val=min)
             * and 7 (val=max) to select index. */
            tmp  = (alp >= dist4) ? -1 : 0;
            ind  = tmp & 4;
            alp -= dist4 & tmp;
            tmp  = (alp >= dist2) ? -1 : 0;
            ind += tmp & 2;
            alp -= dist2 & tmp;
            ind += (alp >= dist);

            /* Turn linear scale into DXT index (0/1 are extreme points) */
            ind  = -ind & 7;
            ind ^= (2 > ind);

            /* Write index */
            mask |= ind << bits;
            bits += 3;
            if (bits >= 8) {
                *dst++ = mask;
                mask >>= 8;
                bits  -= 8;
            }
        }
    }
}

/**
 * Convert a RGBA buffer to unscaled YCoCg.
 * Scale is usually introduced to avoid banding over a certain range of colors,
 * but this version of the algorithm does not introduce it as much as other
 * implementations, allowing for a simpler and faster conversion.
 */
static void rgba2ycocg(uint8_t *dst, const uint8_t *pixel)
{
    int r =  pixel[0];
    int g = (pixel[1] + 1) >> 1;
    int b =  pixel[2];
    int t = (2 + r + b) >> 2;

    int y  = av_clip_uint8(g + t);
    int co = av_clip_uint8(128 + ((r - b + 1) >> 1));
    int cg = av_clip_uint8(128 + g - t);

    dst[0] = (uint8_t) co;
    dst[1] = (uint8_t) cg;
    dst[2] = 0;
    dst[3] = (uint8_t) y;
}

/**
 * Compress one block of RGBA pixels in a DXT1 texture and store the
 * resulting bytes in 'dst'. Alpha is not preserved.
 *
 * @param dst    output buffer.
 * @param stride scanline in bytes.
 * @param block  block to compress.
 * @return how much texture data has been written.
 */
static int dxt1_block(uint8_t *dst, ptrdiff_t stride, const uint8_t *block)
{
    compress_color(dst, stride, block);

    return 8;
}

/**
 * Compress one block of RGBA pixels in a DXT5 texture and store the
 * resulting bytes in 'dst'. Alpha is preserved.
 *
 * @param dst    output buffer.
 * @param stride scanline in bytes.
 * @param block  block to compress.
 * @return how much texture data has been written.
 */
static int dxt5_block(uint8_t *dst, ptrdiff_t stride, const uint8_t *block)
{
    compress_alpha(dst, stride, block);
    compress_color(dst + 8, stride, block);

    return 16;
}

/**
 * Compress one block of RGBA pixels in a DXT5-YCoCg texture and store the
 * resulting bytes in 'dst'. Alpha is not preserved.
 *
 * @param dst    output buffer.
 * @param stride scanline in bytes.
 * @param block  block to compress.
 * @return how much texture data has been written.
 */
static int dxt5ys_block(uint8_t *dst, ptrdiff_t stride, const uint8_t *block)
{
    int x, y;
    uint8_t reorder[64];

    /* Reorder the components and then run a normal DXT5 compression. */
    for (y = 0; y < 4; y++)
        for (x = 0; x < 4; x++)
            rgba2ycocg(reorder + x * 4 + y * 16, block + x * 4 + y * stride);

    compress_alpha(dst + 0, 16, reorder);
    compress_color(dst + 8, 16, reorder);

    return 16;
}

av_cold void ff_texturedspenc_init(TextureDSPContext *c)
{
    c->dxt1_block   = dxt1_block;
    c->dxt5_block   = dxt5_block;
    c->dxt5ys_block = dxt5ys_block;
}