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
28static 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
77void 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
88void 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}
98