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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 "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 w, unsigned int h,
30  unsigned int qstride, unsigned int flag,
31  uint64_t alpha) {
32  unsigned int x, y, c0, c1, a = (!flag * 255u) << 24;
33  unsigned int rb0, rb1, rb2, rb3, g0, g1, g2, g3;
34  uint32_t colors[4], pixels;
35 
36  c0 = bytestream2_get_le16(gb);
37  c1 = bytestream2_get_le16(gb);
38 
39  rb0 = (c0<<3 | c0<<8) & 0xf800f8;
40  rb1 = (c1<<3 | c1<<8) & 0xf800f8;
41  rb0 += (rb0>>5) & 0x070007;
42  rb1 += (rb1>>5) & 0x070007;
43  g0 = (c0 <<5) & 0x00fc00;
44  g1 = (c1 <<5) & 0x00fc00;
45  g0 += (g0 >>6) & 0x000300;
46  g1 += (g1 >>6) & 0x000300;
47 
48  colors[0] = rb0 + g0 + a;
49  colors[1] = rb1 + g1 + a;
50 
51  if (c0 > c1 || flag) {
52  rb2 = (((2*rb0+rb1) * 21) >> 6) & 0xff00ff;
53  rb3 = (((2*rb1+rb0) * 21) >> 6) & 0xff00ff;
54  g2 = (((2*g0 +g1 ) * 21) >> 6) & 0x00ff00;
55  g3 = (((2*g1 +g0 ) * 21) >> 6) & 0x00ff00;
56  colors[3] = rb3 + g3 + a;
57  } else {
58  rb2 = ((rb0+rb1) >> 1) & 0xff00ff;
59  g2 = ((g0 +g1 ) >> 1) & 0x00ff00;
60  colors[3] = 0;
61  }
62 
63  colors[2] = rb2 + g2 + a;
64 
65  pixels = bytestream2_get_le32(gb);
66  for (y=0; y<h; y++) {
67  for (x=0; x<w; x++) {
68  a = (alpha & 0x0f) << 28;
69  a += a >> 4;
70  d[x] = a + colors[pixels&3];
71  pixels >>= 2;
72  alpha >>= 4;
73  }
74  for (; x<4; x++) {
75  pixels >>= 2;
76  alpha >>= 4;
77  }
78  d += qstride;
79  }
80 }
81 
83  const unsigned int w, const unsigned int h,
84  const unsigned int stride) {
85  unsigned int x, y, qstride = stride/4;
86  uint32_t *d = (uint32_t *) dst;
87 
88  for (y=0; y < h; y += 4, d += stride-w)
89  for (x = 0; x < w; d += FFMIN(4, w-x), x += 4)
90  dxt1_decode_pixels(gb, d, FFMIN(4, w-x), FFMIN(4, h-y), qstride, 0, 0LL);
91 }
92 
94  const unsigned int w, const unsigned int h,
95  const unsigned int stride) {
96  unsigned int x, y, qstride = stride/4;
97  uint32_t *d = (uint32_t *) dst;
98 
99  for (y=0; y < h; y += 4, d += stride-w)
100  for (x = 0; x < w; d += FFMIN(4, w-x), x += 4)
101  dxt1_decode_pixels(gb, d, FFMIN(4, w-x), FFMIN(4, h-y), qstride, 1, bytestream2_get_le64(gb));
102 }