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ffmpeg / libavcodec / s3tc.c @ 2912e87a

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/*
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 * S3 Texture Compression (S3TC) decoding functions
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 * Copyright (c) 2007 by Ivo van Poorten
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 *
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 * see also: http://wiki.multimedia.cx/index.php?title=S3TC
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 *
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 * This file is part of Libav.
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 *
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 * Libav is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * Libav is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with Libav; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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#include "libavutil/intreadwrite.h"
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#include "avcodec.h"
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#include "s3tc.h"
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static inline void dxt1_decode_pixels(const uint8_t *s, uint32_t *d,
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                                      unsigned int qstride, unsigned int flag,
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                                      uint64_t alpha) {
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    unsigned int x, y, c0, c1, a = (!flag * 255) << 24;
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    unsigned int rb0, rb1, rb2, rb3, g0, g1, g2, g3;
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    uint32_t colors[4], pixels;
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    c0 = AV_RL16(s);
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    c1 = AV_RL16(s+2);
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    rb0  = (c0<<3 | c0<<8) & 0xf800f8;
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    rb1  = (c1<<3 | c1<<8) & 0xf800f8;
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    rb0 +=        (rb0>>5) & 0x070007;
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    rb1 +=        (rb1>>5) & 0x070007;
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    g0   =        (c0 <<5) & 0x00fc00;
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    g1   =        (c1 <<5) & 0x00fc00;
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    g0  +=        (g0 >>6) & 0x000300;
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    g1  +=        (g1 >>6) & 0x000300;
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    colors[0] = rb0 + g0 + a;
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    colors[1] = rb1 + g1 + a;
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    if (c0 > c1 || flag) {
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        rb2 = (((2*rb0+rb1) * 21) >> 6) & 0xff00ff;
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        rb3 = (((2*rb1+rb0) * 21) >> 6) & 0xff00ff;
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        g2  = (((2*g0 +g1 ) * 21) >> 6) & 0x00ff00;
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        g3  = (((2*g1 +g0 ) * 21) >> 6) & 0x00ff00;
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        colors[3] = rb3 + g3 + a;
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    } else {
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        rb2 = ((rb0+rb1) >> 1) & 0xff00ff;
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        g2  = ((g0 +g1 ) >> 1) & 0x00ff00;
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        colors[3] = 0;
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    }
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    colors[2] = rb2 + g2 + a;
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    pixels = AV_RL32(s+4);
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    for (y=0; y<4; y++) {
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        for (x=0; x<4; x++) {
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            a        = (alpha & 0x0f) << 28;
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            a       += a >> 4;
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            d[x]     = a + colors[pixels&3];
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            pixels >>= 2;
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            alpha  >>= 4;
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        }
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        d += qstride;
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    }
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}
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void ff_decode_dxt1(const uint8_t *s, uint8_t *dst,
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                    const unsigned int w, const unsigned int h,
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                    const unsigned int stride) {
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    unsigned int bx, by, qstride = stride/4;
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    uint32_t *d = (uint32_t *) dst;
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    for (by=0; by < h/4; by++, d += stride-w)
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        for (bx=0; bx < w/4; bx++, s+=8, d+=4)
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            dxt1_decode_pixels(s, d, qstride, 0, 0LL);
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}
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void ff_decode_dxt3(const uint8_t *s, uint8_t *dst,
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                    const unsigned int w, const unsigned int h,
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                    const unsigned int stride) {
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    unsigned int bx, by, qstride = stride/4;
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    uint32_t *d = (uint32_t *) dst;
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    for (by=0; by < h/4; by++, d += stride-w)
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        for (bx=0; bx < w/4; bx++, s+=16, d+=4)
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            dxt1_decode_pixels(s+8, d, qstride, 1, AV_RL64(s));
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}