libavcodec/rle.c

   1 /*
   2  * RLE encoder
   3  * Copyright (c) 2007 Bobby Bingham
   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 "avcodec.h"
  22 #include "rle.h"
  23
  24 /**
  25  * Count up to 127 consecutive pixels which are either all the same or
  26  * all differ from the previous and next pixels.
  27  * @param start Pointer to the first pixel
  28  * @param len Maximum number of pixels
  29  * @param bpp Bytes per pixel
  30  * @param same 1 if searching for identical pixel values.  0 for differing
  31  * @return Number of matching consecutive pixels found
  32  */
  33 static int count_pixels(const uint8_t *start, int len, int bpp, int same)
  34 {
  35     const uint8_t *pos;
  36     int count = 1;
  37
  38     for(pos = start + bpp; count < FFMIN(127, len); pos += bpp, count ++) {
  39         if(same != !memcmp(pos-bpp, pos, bpp)) {
  40             if(!same) {
  41                 /* if bpp == 1, then 0 1 1 0 is more efficiently encoded as a single
  42                  * raw block of pixels.  for larger bpp, RLE is as good or better */
  43                 if(bpp == 1 && count + 1 < FFMIN(127, len) && *pos != *(pos+1))
  44                     continue;
  45
  46                 /* if RLE can encode the next block better than as a raw block,
  47                  * back up and leave _all_ the identical pixels for RLE */
  48                 count --;
  49             }
  50             break;
  51         }
  52     }
  53
  54     return count;
  55 }
  56
  57 int ff_rle_encode(uint8_t *outbuf, int out_size, const uint8_t *ptr , int bpp, int w,
  58                   int add_rep, int xor_rep, int add_raw, int xor_raw)
  59 {
  60     int count, x;
  61     uint8_t *out = outbuf;
  62
  63     for(x = 0; x < w; x += count) {
  64         /* see if we can encode the next set of pixels with RLE */
  65         if((count = count_pixels(ptr, w-x, bpp, 1)) > 1) {
  66             if(out + bpp + 1 > outbuf + out_size) return -1;
  67             *out++ = (count ^ xor_rep) + add_rep;
  68             memcpy(out, ptr, bpp);
  69             out += bpp;
  70         } else {
  71             /* fall back on uncompressed */
  72             count = count_pixels(ptr, w-x, bpp, 0);
  73             if(out + bpp*count >= outbuf + out_size) return -1;
  74             *out++ = (count ^ xor_raw) + add_raw;
  75
  76             memcpy(out, ptr, bpp * count);
  77             out += bpp * count;
  78         }
  79
  80         ptr += count * bpp;
  81     }
  82
  83     return out - outbuf;
  84 }