libavcodec/png.c

   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     return av_mallocz_array(items, size);
  51 }
  52
  53 void ff_png_zfree(void *opaque, void *ptr)
  54 {
  55     av_free(ptr);
  56 }
  57
  58 int ff_png_get_nb_channels(int color_type)
  59 {
  60     int channels;
  61     channels = 1;
  62     if ((color_type & (PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_PALETTE)) ==
  63         PNG_COLOR_MASK_COLOR)
  64         channels = 3;
  65     if (color_type & PNG_COLOR_MASK_ALPHA)
  66         channels++;
  67     return channels;
  68 }
  69
  70 /* compute the row size of an interleaved pass */
  71 int ff_png_pass_row_size(int pass, int bits_per_pixel, int width)
  72 {
  73     int shift, xmin, pass_width;
  74
  75     xmin = ff_png_pass_xmin[pass];
  76     if (width <= xmin)
  77         return 0;
  78     shift      = ff_png_pass_xshift[pass];
  79     pass_width = (width - xmin + (1 << shift) - 1) >> shift;
  80     return (pass_width * bits_per_pixel + 7) >> 3;
  81 }