FFmpeg
png.c
Go to the documentation of this file.
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 
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)) ==
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 */
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;
62  pass_width = (width - xmin + (1 << shift) - 1) >> shift;
63  return (pass_width * bits_per_pixel + 7) >> 3;
64 }
ff_png_get_nb_channels
int ff_png_get_nb_channels(int color_type)
Definition: png.c:41
ff_png_pass_xmin
static const uint8_t ff_png_pass_xmin[NB_PASSES]
Definition: png.c:32
NB_PASSES
#define NB_PASSES
Definition: png.h:47
ff_png_pass_row_size
int ff_png_pass_row_size(int pass, int bits_per_pixel, int width)
Definition: png.c:54
width
#define width
channels
channels
Definition: aptx.h:31
pass
#define pass
Definition: fft_template.c:608
ff_png_pass_ymask
const uint8_t ff_png_pass_ymask[NB_PASSES]
Definition: png.c:27
shift
static int shift(int a, int b)
Definition: bonk.c:260
PNG_COLOR_MASK_COLOR
#define PNG_COLOR_MASK_COLOR
Definition: png.h:30
PNG_COLOR_MASK_PALETTE
#define PNG_COLOR_MASK_PALETTE
Definition: png.h:29
mem.h
png.h
PNG_COLOR_MASK_ALPHA
#define PNG_COLOR_MASK_ALPHA
Definition: png.h:31
ff_png_pass_xshift
static const uint8_t ff_png_pass_xshift[NB_PASSES]
Definition: png.c:37