ffmpeg/libavcodec/png.c

   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 #include "avcodec.h"
  22 #include "png.h"
  23
  24 /* Mask to determine which y pixels are valid in a pass */
  25 const uint8_t ff_png_pass_ymask[NB_PASSES] = {
  26     0x80, 0x80, 0x08, 0x88, 0x22, 0xaa, 0x55,
  27 };
  28
  29 /* minimum x value */
  30 static const uint8_t ff_png_pass_xmin[NB_PASSES] = {
  31     0, 4, 0, 2, 0, 1, 0
  32 };
  33
  34 /* x shift to get row width */
  35 static const uint8_t ff_png_pass_xshift[NB_PASSES] = {
  36     3, 3, 2, 2, 1, 1, 0
  37 };
  38
  39 void *ff_png_zalloc(void *opaque, unsigned int items, unsigned int size)
  40 {
  41     return av_mallocz_array(items, size);
  42 }
  43
  44 void ff_png_zfree(void *opaque, void *ptr)
  45 {
  46     av_free(ptr);
  47 }
  48
  49 int ff_png_get_nb_channels(int color_type)
  50 {
  51     int channels;
  52     channels = 1;
  53     if ((color_type & (PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_PALETTE)) ==
  54         PNG_COLOR_MASK_COLOR)
  55         channels = 3;
  56     if (color_type & PNG_COLOR_MASK_ALPHA)
  57         channels++;
  58     return channels;
  59 }
  60
  61 /* compute the row size of an interleaved pass */
  62 int ff_png_pass_row_size(int pass, int bits_per_pixel, int width)
  63 {
  64     int shift, xmin, pass_width;
  65
  66     xmin = ff_png_pass_xmin[pass];
  67     if (width <= xmin)
  68         return 0;
  69     shift      = ff_png_pass_xshift[pass];
  70     pass_width = (width - xmin + (1 << shift) - 1) >> shift;
  71     return (pass_width * bits_per_pixel + 7) >> 3;
  72 }