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src/Source/LibPNG/pngread.c  view on Meta::CPAN

    * sets the png_struct fields; that's all we are interested in here.  The
    * precise interaction with an app call to png_set_tRNS and PNG file reading
    * is unclear.
    */
   else if (png_ptr->num_trans > 0)
      format |= PNG_FORMAT_FLAG_ALPHA;

   if (png_ptr->bit_depth == 16)
      format |= PNG_FORMAT_FLAG_LINEAR;

   if ((png_ptr->color_type & PNG_COLOR_MASK_PALETTE) != 0)
      format |= PNG_FORMAT_FLAG_COLORMAP;

   return format;
}

/* Is the given gamma significantly different from sRGB?  The test is the same
 * one used in pngrtran.c when deciding whether to do gamma correction.  The
 * arithmetic optimizes the division by using the fact that the inverse of the
 * file sRGB gamma is 2.2
 */
static int
png_gamma_not_sRGB(png_fixed_point g)
{
   if (g < PNG_FP_1)
   {
      /* An uninitialized gamma is assumed to be sRGB for the simplified API. */
      if (g == 0)
         return 0;

      return png_gamma_significant((g * 11 + 2)/5 /* i.e. *2.2, rounded */);
   }

   return 1;
}

/* Do the main body of a 'png_image_begin_read' function; read the PNG file
 * header and fill in all the information.  This is executed in a safe context,
 * unlike the init routine above.
 */
static int
png_image_read_header(png_voidp argument)
{
   png_imagep image = png_voidcast(png_imagep, argument);
   png_structrp png_ptr = image->opaque->png_ptr;
   png_inforp info_ptr = image->opaque->info_ptr;

   png_set_benign_errors(png_ptr, 1/*warn*/);
   png_read_info(png_ptr, info_ptr);

   /* Do this the fast way; just read directly out of png_struct. */
   image->width = png_ptr->width;
   image->height = png_ptr->height;

   {
      png_uint_32 format = png_image_format(png_ptr);

      image->format = format;

#ifdef PNG_COLORSPACE_SUPPORTED
      /* Does the colorspace match sRGB?  If there is no color endpoint
       * (colorant) information assume yes, otherwise require the
       * 'ENDPOINTS_MATCHP_sRGB' colorspace flag to have been set.  If the
       * colorspace has been determined to be invalid ignore it.
       */
      if ((format & PNG_FORMAT_FLAG_COLOR) != 0 && ((png_ptr->colorspace.flags
         & (PNG_COLORSPACE_HAVE_ENDPOINTS|PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB|
            PNG_COLORSPACE_INVALID)) == PNG_COLORSPACE_HAVE_ENDPOINTS))
         image->flags |= PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB;
#endif
   }

   /* We need the maximum number of entries regardless of the format the
    * application sets here.
    */
   {
      png_uint_32 cmap_entries;

      switch (png_ptr->color_type)
      {
         case PNG_COLOR_TYPE_GRAY:
            cmap_entries = 1U << png_ptr->bit_depth;
            break;

         case PNG_COLOR_TYPE_PALETTE:
            cmap_entries = png_ptr->num_palette;
            break;

         default:
            cmap_entries = 256;
            break;
      }

      if (cmap_entries > 256)
         cmap_entries = 256;

      image->colormap_entries = cmap_entries;
   }

   return 1;
}

#ifdef PNG_STDIO_SUPPORTED
int PNGAPI
png_image_begin_read_from_stdio(png_imagep image, FILE* file)
{
   if (image != NULL && image->version == PNG_IMAGE_VERSION)
   {
      if (file != NULL)
      {
         if (png_image_read_init(image) != 0)
         {
            /* This is slightly evil, but png_init_io doesn't do anything other
             * than this and we haven't changed the standard IO functions so
             * this saves a 'safe' function.
             */
            image->opaque->png_ptr->io_ptr = file;
            return png_safe_execute(image, png_image_read_header, image);
         }
      }