libavcodec/rtjpeg.c

   1 /*
   2  * RTJpeg decoding functions
   3  * Copyright (c) 2006 Reimar Doeffinger
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21 #include "libavutil/common.h"
  22 #include "get_bits.h"
  23 #include "dsputil.h"
  24 #include "rtjpeg.h"
  25
  26 #define PUT_COEFF(c) \
  27     i = scan[coeff--]; \
  28     block[i] = (c) * quant[i];
  29
  30 //! aligns the bitstream to the give power of two
  31 #define ALIGN(a) \
  32     n = (-get_bits_count(gb)) & (a - 1); \
  33     if (n) {skip_bits(gb, n);}
  34
  35 /**
  36  * \brief read one block from stream
  37  * \param gb contains stream data
  38  * \param block where data is written to
  39  * \param scan array containing the mapping stream address -> block position
  40  * \param quant quantization factors
  41  * \return 0 means the block is not coded, < 0 means an error occurred.
  42  *
  43  * Note: GetBitContext is used to make the code simpler, since all data is
  44  * aligned this could be done faster in a different way, e.g. as it is done
  45  * in MPlayer libmpcodecs/native/rtjpegn.c.
  46  */
  47 static inline int get_block(GetBitContext *gb, DCTELEM *block, const uint8_t *scan,
  48                             const uint32_t *quant) {
  49     int coeff, i, n;
  50     int8_t ac;
  51     uint8_t dc = get_bits(gb, 8);
  52
  53     // block not coded
  54     if (dc == 255)
  55        return 0;
  56
  57     // number of non-zero coefficients
  58     coeff = get_bits(gb, 6);
  59     if (get_bits_count(gb) + (coeff << 1) >= gb->size_in_bits)
  60         return -1;
  61
  62     // normally we would only need to clear the (63 - coeff) last values,
  63     // but since we do not know where they are we just clear the whole block
  64     memset(block, 0, 64 * sizeof(DCTELEM));
  65
  66     // 2 bits per coefficient
  67     while (coeff) {
  68         ac = get_sbits(gb, 2);
  69         if (ac == -2)
  70             break; // continue with more bits
  71         PUT_COEFF(ac);
  72     }
  73
  74     // 4 bits per coefficient
  75     ALIGN(4);
  76     if (get_bits_count(gb) + (coeff << 2) >= gb->size_in_bits)
  77         return -1;
  78     while (coeff) {
  79         ac = get_sbits(gb, 4);
  80         if (ac == -8)
  81             break; // continue with more bits
  82         PUT_COEFF(ac);
  83     }
  84
  85     // 8 bits per coefficient
  86     ALIGN(8);
  87     if (get_bits_count(gb) + (coeff << 3) >= gb->size_in_bits)
  88         return -1;
  89     while (coeff) {
  90         ac = get_sbits(gb, 8);
  91         PUT_COEFF(ac);
  92     }
  93
  94     PUT_COEFF(dc);
  95     return 1;
  96 }
  97
  98 /**
  99  * \brief decode one rtjpeg YUV420 frame
 100  * \param c context, must be initialized via rtjpeg_decode_init
 101  * \param f AVFrame to place decoded frame into. If parts of the frame
 102  *          are not coded they are left unchanged, so consider initializing it
 103  * \param buf buffer containing input data
 104  * \param buf_size length of input data in bytes
 105  * \return number of bytes consumed from the input buffer
 106  */
 107 int rtjpeg_decode_frame_yuv420(RTJpegContext *c, AVFrame *f,
 108                                const uint8_t *buf, int buf_size) {
 109     GetBitContext gb;
 110     int w = c->w / 16, h = c->h / 16;
 111     int x, y;
 112     uint8_t *y1 = f->data[0], *y2 = f->data[0] + 8 * f->linesize[0];
 113     uint8_t *u = f->data[1], *v = f->data[2];
 114     init_get_bits(&gb, buf, buf_size * 8);
 115     for (y = 0; y < h; y++) {
 116         for (x = 0; x < w; x++) {
 117             DCTELEM *block = c->block;
 118             if (get_block(&gb, block, c->scan, c->lquant) > 0)
 119                 c->dsp->idct_put(y1, f->linesize[0], block);
 120             y1 += 8;
 121             if (get_block(&gb, block, c->scan, c->lquant) > 0)
 122                 c->dsp->idct_put(y1, f->linesize[0], block);
 123             y1 += 8;
 124             if (get_block(&gb, block, c->scan, c->lquant) > 0)
 125                 c->dsp->idct_put(y2, f->linesize[0], block);
 126             y2 += 8;
 127             if (get_block(&gb, block, c->scan, c->lquant) > 0)
 128                 c->dsp->idct_put(y2, f->linesize[0], block);
 129             y2 += 8;
 130             if (get_block(&gb, block, c->scan, c->cquant) > 0)
 131                 c->dsp->idct_put(u, f->linesize[1], block);
 132             u += 8;
 133             if (get_block(&gb, block, c->scan, c->cquant) > 0)
 134                 c->dsp->idct_put(v, f->linesize[2], block);
 135             v += 8;
 136         }
 137         y1 += 2 * 8 * (f->linesize[0] - w);
 138         y2 += 2 * 8 * (f->linesize[0] - w);
 139         u += 8 * (f->linesize[1] - w);
 140         v += 8 * (f->linesize[2] - w);
 141     }
 142     return get_bits_count(&gb) / 8;
 143 }
 144
 145 /**
 146  * \brief initialize an RTJpegContext, may be called multiple times
 147  * \param c context to initialize
 148  * \param dsp specifies the idct to use for decoding
 149  * \param width width of image, will be rounded down to the nearest multiple
 150  *              of 16 for decoding
 151  * \param height height of image, will be rounded down to the nearest multiple
 152  *              of 16 for decoding
 153  * \param lquant luma quantization table to use
 154  * \param cquant chroma quantization table to use
 155  */
 156 void rtjpeg_decode_init(RTJpegContext *c, DSPContext *dsp,
 157                         int width, int height,
 158                         const uint32_t *lquant, const uint32_t *cquant) {
 159     int i;
 160     c->dsp = dsp;
 161     for (i = 0; i < 64; i++) {
 162         int z = ff_zigzag_direct[i];
 163         int p = c->dsp->idct_permutation[i];
 164         z = ((z << 3) | (z >> 3)) & 63; // rtjpeg uses a transposed variant
 165
 166         // permute the scan and quantization tables for the chosen idct
 167         c->scan[i] = c->dsp->idct_permutation[z];
 168         c->lquant[p] = lquant[i];
 169         c->cquant[p] = cquant[i];
 170     }
 171     c->w = width;
 172     c->h = height;
 173 }