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  1. /*
  2.  * S3 Texture Compression (S3TC) decoding functions
  3.  * Copyright (c) 2007 by Ivo van Poorten
  4.  *
  5.  * see also: http://wiki.multimedia.cx/index.php?title=S3TC
  6.  *
  7.  * This file is part of FFmpeg.
  8.  *
  9.  * FFmpeg is free software; you can redistribute it and/or
  10.  * modify it under the terms of the GNU Lesser General Public
  11.  * License as published by the Free Software Foundation; either
  12.  * version 2.1 of the License, or (at your option) any later version.
  13.  *
  14.  * FFmpeg is distributed in the hope that it will be useful,
  15.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17.  * Lesser General Public License for more details.
  18.  *
  19.  * You should have received a copy of the GNU Lesser General Public
  20.  * License along with FFmpeg; if not, write to the Free Software
  21.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22.  */
  23.  
  24. #include "avcodec.h"
  25. #include "bytestream.h"
  26. #include "s3tc.h"
  27.  
  28. static inline void dxt1_decode_pixels(GetByteContext *gb, uint32_t *d,
  29.                                       unsigned int qstride, unsigned int flag,
  30.                                       uint64_t alpha) {
  31.     unsigned int x, y, c0, c1, a = (!flag * 255u) << 24;
  32.     unsigned int rb0, rb1, rb2, rb3, g0, g1, g2, g3;
  33.     uint32_t colors[4], pixels;
  34.  
  35.     c0 = bytestream2_get_le16(gb);
  36.     c1 = bytestream2_get_le16(gb);
  37.  
  38.     rb0  = (c0<<3 | c0<<8) & 0xf800f8;
  39.     rb1  = (c1<<3 | c1<<8) & 0xf800f8;
  40.     rb0 +=        (rb0>>5) & 0x070007;
  41.     rb1 +=        (rb1>>5) & 0x070007;
  42.     g0   =        (c0 <<5) & 0x00fc00;
  43.     g1   =        (c1 <<5) & 0x00fc00;
  44.     g0  +=        (g0 >>6) & 0x000300;
  45.     g1  +=        (g1 >>6) & 0x000300;
  46.  
  47.     colors[0] = rb0 + g0 + a;
  48.     colors[1] = rb1 + g1 + a;
  49.  
  50.     if (c0 > c1 || flag) {
  51.         rb2 = (((2*rb0+rb1) * 21) >> 6) & 0xff00ff;
  52.         rb3 = (((2*rb1+rb0) * 21) >> 6) & 0xff00ff;
  53.         g2  = (((2*g0 +g1 ) * 21) >> 6) & 0x00ff00;
  54.         g3  = (((2*g1 +g0 ) * 21) >> 6) & 0x00ff00;
  55.         colors[3] = rb3 + g3 + a;
  56.     } else {
  57.         rb2 = ((rb0+rb1) >> 1) & 0xff00ff;
  58.         g2  = ((g0 +g1 ) >> 1) & 0x00ff00;
  59.         colors[3] = 0;
  60.     }
  61.  
  62.     colors[2] = rb2 + g2 + a;
  63.  
  64.     pixels = bytestream2_get_le32(gb);
  65.     for (y=0; y<4; y++) {
  66.         for (x=0; x<4; x++) {
  67.             a        = (alpha & 0x0f) << 28;
  68.             a       += a >> 4;
  69.             d[x]     = a + colors[pixels&3];
  70.             pixels >>= 2;
  71.             alpha  >>= 4;
  72.         }
  73.         d += qstride;
  74.     }
  75. }
  76.  
  77. void ff_decode_dxt1(GetByteContext *gb, uint8_t *dst,
  78.                     const unsigned int w, const unsigned int h,
  79.                     const unsigned int stride) {
  80.     unsigned int bx, by, qstride = stride/4;
  81.     uint32_t *d = (uint32_t *) dst;
  82.  
  83.     for (by=0; by < h/4; by++, d += stride-w)
  84.         for (bx = 0; bx < w / 4; bx++, d += 4)
  85.             dxt1_decode_pixels(gb, d, qstride, 0, 0LL);
  86. }
  87.  
  88. void ff_decode_dxt3(GetByteContext *gb, uint8_t *dst,
  89.                     const unsigned int w, const unsigned int h,
  90.                     const unsigned int stride) {
  91.     unsigned int bx, by, qstride = stride/4;
  92.     uint32_t *d = (uint32_t *) dst;
  93.  
  94.     for (by=0; by < h/4; by++, d += stride-w)
  95.         for (bx = 0; bx < w / 4; bx++, d += 4)
  96.             dxt1_decode_pixels(gb, d, qstride, 1, bytestream2_get_le64(gb));
  97. }
  98.