libavcodec/s3tc.c

   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 "libavutil/intreadwrite.h"
  25 #include "avcodec.h"
  26 #include "s3tc.h"
  27
  28 static inline void dxt1_decode_pixels(const uint8_t *s, uint32_t *d,
  29                                       unsigned int qstride, unsigned int flag,
  30                                       uint64_t alpha) {
  31     unsigned int x, y, c0, c1, a = (!flag * 255) << 24;
  32     unsigned int rb0, rb1, rb2, rb3, g0, g1, g2, g3;
  33     uint32_t colors[4], pixels;
  34
  35     c0 = AV_RL16(s);
  36     c1 = AV_RL16(s+2);
  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 = AV_RL32(s+4);
  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(const uint8_t *s, 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++, s+=8, d+=4)
  85             dxt1_decode_pixels(s, d, qstride, 0, 0LL);
  86 }
  87
  88 void ff_decode_dxt3(const uint8_t *s, 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++, s+=16, d+=4)
  96             dxt1_decode_pixels(s+8, d, qstride, 1, AV_RL64(s));
  97 }