png.c
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1 /*
2  * PNG image format
3  * Copyright (c) 2003 Fabrice Bellard
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 "bytestream.h"
23 #include "png.h"
24 
25 const uint8_t ff_pngsig[8] = {137, 80, 78, 71, 13, 10, 26, 10};
26 const uint8_t ff_mngsig[8] = {138, 77, 78, 71, 13, 10, 26, 10};
27 
28 /* Mask to determine which y pixels are valid in a pass */
29 const uint8_t ff_png_pass_ymask[NB_PASSES] = {
30  0x80, 0x80, 0x08, 0x88, 0x22, 0xaa, 0x55,
31 };
32 
33 /* minimum x value */
34 static const uint8_t ff_png_pass_xmin[NB_PASSES] = {
35  0, 4, 0, 2, 0, 1, 0
36 };
37 
38 /* x shift to get row width */
39 static const uint8_t ff_png_pass_xshift[NB_PASSES] = {
40  3, 3, 2, 2, 1, 1, 0
41 };
42 
43 /* Mask to determine which pixels are valid in a pass */
44 const uint8_t ff_png_pass_mask[NB_PASSES] = {
45  0x80, 0x08, 0x88, 0x22, 0xaa, 0x55, 0xff
46 };
47 
48 void *ff_png_zalloc(void *opaque, unsigned int items, unsigned int size)
49 {
50  if(items >= UINT_MAX / size)
51  return NULL;
52  return av_malloc(items * size);
53 }
54 
55 void ff_png_zfree(void *opaque, void *ptr)
56 {
57  av_free(ptr);
58 }
59 
60 int ff_png_get_nb_channels(int color_type)
61 {
62  int channels;
63  channels = 1;
64  if ((color_type & (PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_PALETTE)) ==
66  channels = 3;
67  if (color_type & PNG_COLOR_MASK_ALPHA)
68  channels++;
69  return channels;
70 }
71 
72 /* compute the row size of an interleaved pass */
73 int ff_png_pass_row_size(int pass, int bits_per_pixel, int width)
74 {
75  int shift, xmin, pass_width;
76 
77  xmin = ff_png_pass_xmin[pass];
78  if (width <= xmin)
79  return 0;
80  shift = ff_png_pass_xshift[pass];
81  pass_width = (width - xmin + (1 << shift) - 1) >> shift;
82  return (pass_width * bits_per_pixel + 7) >> 3;
83 }