rle.c
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1 /*
2  * RLE encoder
3  * Copyright (c) 2007 Bobby Bingham
4  *
5  * This file is part of Libav.
6  *
7  * Libav 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  * Libav 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 Libav; 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 
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 }