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rle.c
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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 #include "libavutil/common.h"
24 
25 /**
26  * Count up to 127 consecutive pixels which are either all the same or
27  * all differ from the previous and next pixels.
28  * @param start Pointer to the first pixel
29  * @param len Maximum number of pixels
30  * @param bpp Bytes per pixel
31  * @param same 1 if searching for identical pixel values. 0 for differing
32  * @return Number of matching consecutive pixels found
33  */
34 static int count_pixels(const uint8_t *start, int len, int bpp, int same)
35 {
36  const uint8_t *pos;
37  int count = 1;
38 
39  for(pos = start + bpp; count < FFMIN(127, len); pos += bpp, count ++) {
40  if(same != !memcmp(pos-bpp, pos, bpp)) {
41  if(!same) {
42  /* if bpp == 1, then 0 1 1 0 is more efficiently encoded as a single
43  * raw block of pixels. for larger bpp, RLE is as good or better */
44  if(bpp == 1 && count + 1 < FFMIN(127, len) && *pos != *(pos+1))
45  continue;
46 
47  /* if RLE can encode the next block better than as a raw block,
48  * back up and leave _all_ the identical pixels for RLE */
49  count --;
50  }
51  break;
52  }
53  }
54 
55  return count;
56 }
57 
58 int ff_rle_encode(uint8_t *outbuf, int out_size, const uint8_t *ptr , int bpp, int w,
59  int add_rep, int xor_rep, int add_raw, int xor_raw)
60 {
61  int count, x;
62  uint8_t *out = outbuf;
63 
64  for(x = 0; x < w; x += count) {
65  /* see if we can encode the next set of pixels with RLE */
66  if((count = count_pixels(ptr, w-x, bpp, 1)) > 1) {
67  if(out + bpp + 1 > outbuf + out_size) return -1;
68  *out++ = (count ^ xor_rep) + add_rep;
69  memcpy(out, ptr, bpp);
70  out += bpp;
71  } else {
72  /* fall back on uncompressed */
73  count = count_pixels(ptr, w-x, bpp, 0);
74  if(out + bpp*count >= outbuf + out_size) return -1;
75  *out++ = (count ^ xor_raw) + add_raw;
76 
77  memcpy(out, ptr, bpp * count);
78  out += bpp * count;
79  }
80 
81  ptr += count * bpp;
82  }
83 
84  return out - outbuf;
85 }