BURG-grub2/video/readers/png.c

/*
 *  GRUB  --  GRand Unified Bootloader
 *  Copyright (C) 2008,2009  Free Software Foundation, Inc.
 *
 *  GRUB is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  GRUB is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <grub/bitmap.h>
#include <grub/types.h>
#include <grub/normal.h>
#include <grub/dl.h>
#include <grub/mm.h>
#include <grub/misc.h>
#include <grub/bufio.h>

/* Uncomment following define to enable PNG debug.  */
//#define PNG_DEBUG

#define PNG_COLOR_MASK_PALETTE	1
#define PNG_COLOR_MASK_COLOR	2
#define PNG_COLOR_MASK_ALPHA	4

#define PNG_COLOR_TYPE_GRAY	0
#define PNG_COLOR_TYPE_PALETTE	(PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_PALETTE)
#define PNG_COLOR_TYPE_RGB	(PNG_COLOR_MASK_COLOR)
#define PNG_COLOR_TYPE_RGBA	(PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_ALPHA)
#define PNG_COLOR_TYPE_GRAYA	(PNG_COLOR_MASK_ALPHA)

#define PNG_COMPRESSION_BASE	0

#define PNG_INTERLACE_NONE	0
#define PNG_INTERLACE_ADAM7	1

#define PNG_FILTER_TYPE_BASE	0

#define PNG_FILTER_VALUE_NONE	0
#define PNG_FILTER_VALUE_SUB	1
#define PNG_FILTER_VALUE_UP	2
#define PNG_FILTER_VALUE_AVG	3
#define PNG_FILTER_VALUE_PAETH	4
#define PNG_FILTER_VALUE_LAST	5

#define PNG_CHUNK_IHDR		0x49484452
#define PNG_CHUNK_IDAT		0x49444154
#define PNG_CHUNK_IEND		0x49454e44

#define Z_DEFLATED		8
#define Z_FLAG_DICT		32

#define INFLATE_STORED		0
#define INFLATE_FIXED		1
#define INFLATE_DYNAMIC		2

#define WSIZE			0x8000

#define DEFLATE_HCLEN_BASE	4
#define DEFLATE_HCLEN_MAX	19
#define DEFLATE_HLIT_BASE	257
#define DEFLATE_HLIT_MAX	288
#define DEFLATE_HDIST_BASE	1
#define DEFLATE_HDIST_MAX	30

#define DEFLATE_HUFF_LEN	16

#ifdef PNG_DEBUG
static grub_command_t cmd;
#endif

struct huff_table
{
  int *values, *maxval, *offset;
  int num_values, max_length;
};

struct grub_png_data
{
  grub_file_t file;
  struct grub_video_bitmap **bitmap;

  int bit_count, bit_save;

  grub_uint32_t next_offset;

  int image_width, image_height, bpp, is_16bit, raw_bytes;
  grub_uint8_t *image_data;

  int inside_idat, idat_remain;

  int code_values[DEFLATE_HLIT_MAX];
  int code_maxval[DEFLATE_HUFF_LEN];
  int code_offset[DEFLATE_HUFF_LEN];

  int dist_values[DEFLATE_HDIST_MAX];
  int dist_maxval[DEFLATE_HUFF_LEN];
  int dist_offset[DEFLATE_HUFF_LEN];

  struct huff_table code_table;
  struct huff_table dist_table;

  grub_uint8_t slide[WSIZE];
  int wp;

  grub_uint8_t *cur_rgb;

  int cur_column, cur_filter, first_line;
};

static grub_uint32_t
grub_png_get_dword (struct grub_png_data *data)
{
  grub_uint32_t r;

  r = 0;
  grub_file_read (data->file, &r, sizeof (grub_uint32_t));

  return grub_be_to_cpu32 (r);
}

static grub_uint8_t
grub_png_get_byte (struct grub_png_data *data)
{
  grub_uint8_t r;

  if ((data->inside_idat) && (data->idat_remain == 0))
    {
      grub_uint32_t len, type;

      do
	{
          /* Skip crc checksum.  */
	  grub_png_get_dword (data);

          if (data->file->offset != data->next_offset)
            {
              grub_error (GRUB_ERR_BAD_FILE_TYPE,
                          "png: chunk size error");
              return 0;
            }

	  len = grub_png_get_dword (data);
	  type = grub_png_get_dword (data);
	  if (type != PNG_CHUNK_IDAT)
	    {
	      grub_error (GRUB_ERR_BAD_FILE_TYPE,
			  "png: unexpected end of data");
	      return 0;
	    }

          data->next_offset = data->file->offset + len + 4;
	}
      while (len == 0);
      data->idat_remain = len;
    }

  r = 0;
  grub_file_read (data->file, &r, 1);

  if (data->inside_idat)
    data->idat_remain--;

  return r;
}

static int
grub_png_get_bits (struct grub_png_data *data, int num)
{
  int code, shift;

  if (data->bit_count == 0)
    {
      data->bit_save = grub_png_get_byte (data);
      data->bit_count = 8;
    }

  code = 0;
  shift = 0;
  while (grub_errno == 0)
    {
      int n;

      n = data->bit_count;
      if (n > num)
	n = num;

      code += (int) (data->bit_save & ((1 << n) - 1)) << shift;
      num -= n;
      if (!num)
	{
	  data->bit_count -= n;
	  data->bit_save >>= n;
	  break;
	}

      shift += n;

      data->bit_save = grub_png_get_byte (data);
      data->bit_count = 8;
    }

  return code;
}

static grub_err_t
grub_png_decode_image_header (struct grub_png_data *data)
{
  int color_type;
  int color_bits;

  data->image_width = grub_png_get_dword (data);
  data->image_height = grub_png_get_dword (data);

  if ((!data->image_height) || (!data->image_width))
    return grub_error (GRUB_ERR_BAD_FILE_TYPE, "png: invalid image size");

  color_bits = grub_png_get_byte (data);
  if ((color_bits != 8) && (color_bits != 16))
    return grub_error (GRUB_ERR_BAD_FILE_TYPE,
                       "png: bit depth must be 8 or 16");
  data->is_16bit = (color_bits == 16);

  color_type = grub_png_get_byte (data);
  if (color_type == PNG_COLOR_TYPE_RGB)
    {
      if (grub_video_bitmap_create (data->bitmap, data->image_width,
				    data->image_height,
				    GRUB_VIDEO_BLIT_FORMAT_RGB_888))
	return grub_errno;
      data->bpp = 3;
    }
  else if (color_type == PNG_COLOR_TYPE_RGBA)
    {
      if (grub_video_bitmap_create (data->bitmap, data->image_width,
				    data->image_height,
				    GRUB_VIDEO_BLIT_FORMAT_RGBA_8888))
	return grub_errno;
      data->bpp = 4;
    }
  else
    return grub_error (GRUB_ERR_BAD_FILE_TYPE,
		       "png: color type not supported");

  if (data->is_16bit)
    {
      data->bpp <<= 1;

      data->image_data = grub_malloc (data->image_height *
                                      data->image_width *  data->bpp);
      if (grub_errno)
        return grub_errno;

      data->cur_rgb = data->image_data;
    }
  else
    {
      data->image_data = 0;
      data->cur_rgb = (*data->bitmap)->data;
    }

  data->raw_bytes = data->image_height * (data->image_width + 1) * data->bpp;

  data->cur_column = 0;
  data->first_line = 1;

  if (grub_png_get_byte (data) != PNG_COMPRESSION_BASE)
    return grub_error (GRUB_ERR_BAD_FILE_TYPE,
		       "png: compression method not supported");

  if (grub_png_get_byte (data) != PNG_FILTER_TYPE_BASE)
    return grub_error (GRUB_ERR_BAD_FILE_TYPE,
		       "png: filter method not supported");

  if (grub_png_get_byte (data) != PNG_INTERLACE_NONE)
    return grub_error (GRUB_ERR_BAD_FILE_TYPE,
		       "png: interlace method not supported");

  /* Skip crc checksum.  */
  grub_png_get_dword (data);

  return grub_errno;
}

/* Order of the bit length code lengths.  */
static const grub_uint8_t bitorder[] = {
  16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
};

/* Copy lengths for literal codes 257..285.  */
static const int cplens[] = {
  3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
  35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0
};

/* Extra bits for literal codes 257..285.  */
static const grub_uint8_t cplext[] = {
  0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2,
  3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0, 99, 99
};				/* 99==invalid  */

/* Copy offsets for distance codes 0..29.  */
static const int cpdist[] = {
  1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
  257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
  8193, 12289, 16385, 24577
};

/* Extra bits for distance codes.  */
static const grub_uint8_t cpdext[] = {
  0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
  7, 7, 8, 8, 9, 9, 10, 10, 11, 11,
  12, 12, 13, 13
};

static void
grub_png_init_huff_table (struct huff_table *ht, int cur_maxlen,
			  int *cur_values, int *cur_maxval, int *cur_offset)
{
  ht->values = cur_values;
  ht->maxval = cur_maxval;
  ht->offset = cur_offset;
  ht->num_values = 0;
  ht->max_length = cur_maxlen;
  grub_memset (cur_maxval, 0, sizeof (int) * cur_maxlen);
}

static void
grub_png_insert_huff_item (struct huff_table *ht, int code, int len)
{
  int i, n;

  if (len == 0)
    return;

  if (len > ht->max_length)
    {
      grub_error (GRUB_ERR_BAD_FILE_TYPE, "png: invalid code length");
      return;
    }

  n = 0;
  for (i = len; i < ht->max_length; i++)
    n += ht->maxval[i];

  for (i = 0; i < n; i++)
    ht->values[ht->num_values - i] = ht->values[ht->num_values - i - 1];

  ht->values[ht->num_values - n] = code;
  ht->num_values++;
  ht->maxval[len - 1]++;
}

static void
grub_png_build_huff_table (struct huff_table *ht)
{
  int base, ofs, i;

  base = 0;
  ofs = 0;
  for (i = 0; i < ht->max_length; i++)
    {
      base += ht->maxval[i];
      ofs += ht->maxval[i];

      ht->maxval[i] = base;
      ht->offset[i] = ofs - base;

      base <<= 1;
    }
}

static int
grub_png_get_huff_code (struct grub_png_data *data, struct huff_table *ht)
{
  int code, i;

  code = 0;
  for (i = 0; i < ht->max_length; i++)
    {
      code = (code << 1) + grub_png_get_bits (data, 1);
      if (code < ht->maxval[i])
	return ht->values[code + ht->offset[i]];
    }
  return 0;
}

static grub_err_t
grub_png_init_fixed_block (struct grub_png_data *data)
{
  int i;

  grub_png_init_huff_table (&data->code_table, DEFLATE_HUFF_LEN,
			    data->code_values, data->code_maxval,
			    data->code_offset);

  for (i = 0; i < 144; i++)
    grub_png_insert_huff_item (&data->code_table, i, 8);

  for (; i < 256; i++)
    grub_png_insert_huff_item (&data->code_table, i, 9);

  for (; i < 280; i++)
    grub_png_insert_huff_item (&data->code_table, i, 7);

  for (; i < DEFLATE_HLIT_MAX; i++)
    grub_png_insert_huff_item (&data->code_table, i, 8);

  grub_png_build_huff_table (&data->code_table);

  grub_png_init_huff_table (&data->dist_table, DEFLATE_HUFF_LEN,
			    data->dist_values, data->dist_maxval,
			    data->dist_offset);

  for (i = 0; i < DEFLATE_HDIST_MAX; i++)
    grub_png_insert_huff_item (&data->dist_table, i, 5);

  grub_png_build_huff_table (&data->dist_table);

  return grub_errno;
}

static grub_err_t
grub_png_init_dynamic_block (struct grub_png_data *data)
{
  int nl, nd, nb, i, prev;
  struct huff_table cl;
  int cl_values[sizeof (bitorder)];
  int cl_maxval[8];
  int cl_offset[8];
  grub_uint8_t lens[DEFLATE_HCLEN_MAX];

  nl = DEFLATE_HLIT_BASE + grub_png_get_bits (data, 5);
  nd = DEFLATE_HDIST_BASE + grub_png_get_bits (data, 5);
  nb = DEFLATE_HCLEN_BASE + grub_png_get_bits (data, 4);

  if ((nl > DEFLATE_HLIT_MAX) || (nd > DEFLATE_HDIST_MAX) ||
      (nb > DEFLATE_HCLEN_MAX))
    return grub_error (GRUB_ERR_BAD_FILE_TYPE, "png: too much data");

  grub_png_init_huff_table (&cl, 8, cl_values, cl_maxval, cl_offset);

  for (i = 0; i < nb; i++)
    lens[bitorder[i]] = grub_png_get_bits (data, 3);

  for (; i < DEFLATE_HCLEN_MAX; i++)
    lens[bitorder[i]] = 0;

  for (i = 0; i < DEFLATE_HCLEN_MAX; i++)
    grub_png_insert_huff_item (&cl, i, lens[i]);

  grub_png_build_huff_table (&cl);

  grub_png_init_huff_table (&data->code_table, DEFLATE_HUFF_LEN,
			    data->code_values, data->code_maxval,
			    data->code_offset);

  grub_png_init_huff_table (&data->dist_table, DEFLATE_HUFF_LEN,
			    data->dist_values, data->dist_maxval,
			    data->dist_offset);

  prev = 0;
  for (i = 0; i < nl + nd; i++)
    {
      int n, code;
      struct huff_table *ht;

      if (grub_errno)
	return grub_errno;

      if (i < nl)
	{
	  ht = &data->code_table;
	  code = i;
	}
      else
	{
	  ht = &data->dist_table;
	  code = i - nl;
	}

      n = grub_png_get_huff_code (data, &cl);
      if (n < 16)
	{
	  grub_png_insert_huff_item (ht, code, n);
	  prev = n;
	}
      else if (n == 16)
	{
	  int c;

	  c = 3 + grub_png_get_bits (data, 2);
	  while (c > 0)
	    {
	      grub_png_insert_huff_item (ht, code++, prev);
	      i++;
	      c--;
	    }
	  i--;
	}
      else if (n == 17)
	i += 3 + grub_png_get_bits (data, 3) - 1;
      else
	i += 11 + grub_png_get_bits (data, 7) - 1;
    }

  grub_png_build_huff_table (&data->code_table);
  grub_png_build_huff_table (&data->dist_table);

  return grub_errno;
}

static grub_err_t
grub_png_output_byte (struct grub_png_data *data, grub_uint8_t n)
{
  int row_bytes;

  if (--data->raw_bytes < 0)
    return grub_error (GRUB_ERR_BAD_FILE_TYPE, "image size overflown");

  if (data->cur_column == 0)
    {
      if (n >= PNG_FILTER_VALUE_LAST)
	return grub_error (GRUB_ERR_BAD_FILE_TYPE, "invalid filter value");

      data->cur_filter = n;
    }
  else
    *(data->cur_rgb++) = n;

  data->cur_column++;
  row_bytes = data->image_width * data->bpp;
  if (data->cur_column == row_bytes + 1)
    {
      grub_uint8_t *blank_line = NULL;
      grub_uint8_t *cur = data->cur_rgb - row_bytes;
      grub_uint8_t *left = cur;
      grub_uint8_t *up;

      if (data->first_line)
	{
	  blank_line = grub_zalloc (row_bytes);
	  if (blank_line == NULL)
	    return grub_errno;

	  up = blank_line;
	}
      else
	up = cur - row_bytes;

      switch (data->cur_filter)
	{
	case PNG_FILTER_VALUE_SUB:
	  {
	    int i;

	    cur += data->bpp;
	    for (i = data->bpp; i < row_bytes; i++, cur++, left++)
	      *cur += *left;

	    break;
	  }
	case PNG_FILTER_VALUE_UP:
	  {
	    int i;

	    for (i = 0; i < row_bytes; i++, cur++, up++)
	      *cur += *up;

	    break;
	  }
	case PNG_FILTER_VALUE_AVG:
	  {
	    int i;

	    for (i = 0; i < data->bpp; i++, cur++, up++)
	      *cur += *up >> 1;

	    for (; i < row_bytes; i++, cur++, up++, left++)
	      *cur += ((int) *up + (int) *left) >> 1;

	    break;
	  }
	case PNG_FILTER_VALUE_PAETH:
	  {
	    int i;
	    grub_uint8_t *upper_left = up;

	    for (i = 0; i < data->bpp; i++, cur++, up++)
	      *cur += *up;

	    for (; i < row_bytes; i++, cur++, up++, left++, upper_left++)
	      {
		int a, b, c, pa, pb, pc;

                a = *left;
                b = *up;
                c = *upper_left;

                pa = b - c;
                pb = a - c;
                pc = pa + pb;

                if (pa < 0)
                  pa = -pa;

                if (pb < 0)
                  pb = -pb;

                if (pc < 0)
                  pc = -pc;

                *cur += ((pa <= pb) && (pa <= pc)) ? a : (pb <= pc) ? b : c;
	      }
	  }
	}

      if (blank_line)
	grub_free (blank_line);

      data->cur_column = 0;
      data->first_line = 0;
    }

  return grub_errno;
}

static grub_err_t
grub_png_read_dynamic_block (struct grub_png_data *data)
{
  while (grub_errno == 0)
    {
      int n;

      n = grub_png_get_huff_code (data, &data->code_table);
      if (n < 256)
	{
	  data->slide[data->wp] = n;
	  grub_png_output_byte (data, n);

	  data->wp++;
	  if (data->wp >= WSIZE)
	    data->wp = 0;
	}
      else if (n == 256)
	break;
      else
	{
	  int len, dist, pos;

	  n -= 257;
	  len = cplens[n];
	  if (cplext[n])
	    len += grub_png_get_bits (data, cplext[n]);

	  n = grub_png_get_huff_code (data, &data->dist_table);
	  dist = cpdist[n];
	  if (cpdext[n])
	    dist += grub_png_get_bits (data, cpdext[n]);

	  pos = data->wp - dist;
	  if (pos < 0)
	    pos += WSIZE;

	  while (len > 0)
	    {
	      data->slide[data->wp] = data->slide[pos];
	      grub_png_output_byte (data, data->slide[data->wp]);

	      data->wp++;
	      if (data->wp >= WSIZE)
		data->wp = 0;

	      pos++;
	      if (pos >= WSIZE)
		pos = 0;

	      len--;
	    }
	}
    }

  return grub_errno;
}

static grub_err_t
grub_png_decode_image_data (struct grub_png_data *data)
{
  grub_uint8_t cmf, flg;
  int final;

  cmf = grub_png_get_byte (data);
  flg = grub_png_get_byte (data);

  if ((cmf & 0xF) != Z_DEFLATED)
    return grub_error (GRUB_ERR_BAD_FILE_TYPE,
		       "png: only support deflate compression method");

  if (flg & Z_FLAG_DICT)
    return grub_error (GRUB_ERR_BAD_FILE_TYPE,
		       "png: dictionary not supported");

  do
    {
      int block_type;

      final = grub_png_get_bits (data, 1);
      block_type = grub_png_get_bits (data, 2);

      switch (block_type)
	{
	case INFLATE_STORED:
	  {
	    grub_uint16_t i, len;

	    data->bit_count = 0;
	    len = grub_png_get_byte (data);
	    len += ((grub_uint16_t) grub_png_get_byte (data)) << 8;

            /* Skip NLEN field.  */
	    grub_png_get_byte (data);
	    grub_png_get_byte (data);

	    for (i = 0; i < len; i++)
	      grub_png_output_byte (data, grub_png_get_byte (data));

	    break;
	  }

	case INFLATE_FIXED:
          grub_png_init_fixed_block (data);
	  grub_png_read_dynamic_block (data);
	  break;

	case INFLATE_DYNAMIC:
	  grub_png_init_dynamic_block (data);
	  grub_png_read_dynamic_block (data);
	  break;

	default:
	  return grub_error (GRUB_ERR_BAD_FILE_TYPE,
			     "png: unknown block type");
	}
    }
  while ((!final) && (grub_errno == 0));

  /* Skip adler checksum.  */
  grub_png_get_dword (data);

  /* Skip crc checksum.  */
  grub_png_get_dword (data);

  return grub_errno;
}

static const grub_uint8_t png_magic[8] =
  { 0x89, 0x50, 0x4e, 0x47, 0xd, 0xa, 0x1a, 0x0a };

static void
grub_png_convert_image (struct grub_png_data *data)
{
  int i;
  grub_uint8_t *d1, *d2;

  d1 = (*data->bitmap)->data;
  d2 = data->image_data + 1;

  /* Only copy the upper 8 bit.  */
  for (i = 0; i < (data->image_width * data->image_height * data->bpp >> 1);
       i++, d1++, d2+=2)
    *d1 = *d2;
}

static void
grub_png_check_transparency (struct grub_png_data *data)
{
  grub_uint8_t *p;
  int i;

  if (data->bpp != 4)
    return;

  p = (*data->bitmap)->data;
  for (i = 0, p += 3; i < data->image_width * data->image_height; i++, p += 4)
    if (*p != 255)
      {
	(*data->bitmap)->transparent = 1;
	break;
      }
}

static grub_err_t
grub_png_decode_png (struct grub_png_data *data)
{
  grub_uint8_t magic[8];

  if (grub_file_read (data->file, &magic[0], 8) != 8)
    return grub_errno;

  if (grub_memcmp (magic, png_magic, sizeof (png_magic)))
    return grub_error (GRUB_ERR_BAD_FILE_TYPE, "png: not a png file");

  while (1)
    {
      grub_uint32_t len, type;

      len = grub_png_get_dword (data);
      type = grub_png_get_dword (data);
      data->next_offset = data->file->offset + len + 4;

      switch (type)
	{
	case PNG_CHUNK_IHDR:
	  grub_png_decode_image_header (data);
	  break;

	case PNG_CHUNK_IDAT:
	  data->inside_idat = 1;
	  data->idat_remain = len;
	  data->bit_count = 0;

	  grub_png_decode_image_data (data);

	  data->inside_idat = 0;
	  break;

	case PNG_CHUNK_IEND:
          if (data->is_16bit)
            grub_png_convert_image (data);

	  grub_png_check_transparency (data);

	  return grub_errno;

	default:
	  grub_file_seek (data->file, data->file->offset + len + 4);
	}

      if (grub_errno)
        break;

      if (data->file->offset != data->next_offset)
        return grub_error (GRUB_ERR_BAD_FILE_TYPE,
                           "png: chunk size error");
    }

  return grub_errno;
}

static grub_err_t
grub_video_reader_png (struct grub_video_bitmap **bitmap,
		       const char *filename)
{
  grub_file_t file;
  struct grub_png_data *data;

  file = grub_buffile_open (filename, 0);
  if (!file)
    return grub_errno;

  data = grub_zalloc (sizeof (*data));
  if (data != NULL)
    {
      data->file = file;
      data->bitmap = bitmap;

      grub_png_decode_png (data);

      grub_free (data->image_data);
      grub_free (data);
    }

  if (grub_errno != GRUB_ERR_NONE)
    {
      grub_video_bitmap_destroy (*bitmap);
      *bitmap = 0;
    }

  grub_file_close (file);
  return grub_errno;
}

#if defined(PNG_DEBUG)
static grub_err_t
grub_cmd_pngtest (grub_command_t cmd __attribute__ ((unused)),
		  int argc, char **args)
{
  struct grub_video_bitmap *bitmap = 0;

  if (argc != 1)
    return grub_error (GRUB_ERR_BAD_ARGUMENT, "file name required");

  grub_video_reader_png (&bitmap, args[0]);
  if (grub_errno != GRUB_ERR_NONE)
    return grub_errno;

  grub_video_bitmap_destroy (bitmap);

  return GRUB_ERR_NONE;
}
#endif

static struct grub_video_bitmap_reader png_reader = {
  .extension = ".png",
  .reader = grub_video_reader_png,
  .next = 0
};

GRUB_MOD_INIT (png)
{
  grub_video_bitmap_reader_register (&png_reader);
#if defined(PNG_DEBUG)
  cmd = grub_register_command ("pngtest", grub_cmd_pngtest,
			       "FILE",
			       "Tests loading of PNG bitmap.");
#endif
}

GRUB_MOD_FINI (png)
{
#if defined(PNG_DEBUG)
  grub_unregister_command (cmd);
#endif
  grub_video_bitmap_reader_unregister (&png_reader);
}