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s3tc.c
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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 "libavcodec/bytestream.h"
25 #include "avcodec.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 
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 
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 }