1 /*
2 * PNG image format
3 * Copyright (c) 2003 Fabrice Bellard
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
22 #include <stdint.h>
23 #include "libavutil/mem.h"
24 #include "png.h"
25
26 /* Mask to determine which y pixels are valid in a pass */
27 const uint8_t ff_png_pass_ymask[NB_PASSES] = {
28 0x80, 0x80, 0x08, 0x88, 0x22, 0xaa, 0x55,
29 };
30
31 /* minimum x value */
32 static const uint8_t ff_png_pass_xmin[NB_PASSES] = {
33 0, 4, 0, 2, 0, 1, 0
34 };
35
36 /* x shift to get row width */
37 static const uint8_t ff_png_pass_xshift[NB_PASSES] = {
38 3, 3, 2, 2, 1, 1, 0
39 };
40
ff_png_get_nb_channels(int color_type)41 int ff_png_get_nb_channels(int color_type)
42 {
43 int channels;
44 channels = 1;
45 if ((color_type & (PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_PALETTE)) ==
46 PNG_COLOR_MASK_COLOR)
47 channels = 3;
48 if (color_type & PNG_COLOR_MASK_ALPHA)
49 channels++;
50 return channels;
51 }
52
53 /* compute the row size of an interleaved pass */
ff_png_pass_row_size(int pass, int bits_per_pixel, int width)54 int ff_png_pass_row_size(int pass, int bits_per_pixel, int width)
55 {
56 int shift, xmin, pass_width;
57
58 xmin = ff_png_pass_xmin[pass];
59 if (width <= xmin)
60 return 0;
61 shift = ff_png_pass_xshift[pass];
62 pass_width = (width - xmin + (1 << shift) - 1) >> shift;
63 return (pass_width * bits_per_pixel + 7) >> 3;
64 }
65