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