#ifndef _VMUHEADER_H_
#define _VMUHEADER_H_

/* vmu file header */

/*
	http://mc.pp.se/dc

This is the contents of the header:
Offset Size (bytes) Datatype Contents
$00 16 Text Description of file (shown in VMS file menu)
$10 32 Text Description of file (shown in DC boot ROM file manager)
$30 16 String Identifier of application that created the file
$40 2 Integer Number of icons (>1 for animated icons)
$42 2 Integer Icon animation speed
$44 2 Integer Graphic eyecatch type (0 = none)
$46 2 Integer CRC (Ignored for game files.)
$48 4 Integer Number of bytes of actual file data following header,
icon(s) and graphic eyecatch. (Ignored for game files.)
$4C 20 Reserved (fill with zeros)
$60 32 Integers Icon palette (16 16-bit integers)
$80 512*n Nybbles Icon bitmaps
... depends on type ... Graphic eyecatch palette and bitmap

Text fields are padded with space ($20). String fileds are padded with
NUL ($00). Integer fields are little endian.

CRC calculation

The CRC should be computed on the entire file, including header and data
payload, but excluding any padding in the final block. When calcukating
the CRC, set the CRC field itself to 0 to avoid miscalculating the CRC
for the header. The CRC calculation algorithm is as follows (C code):

int calcCRC(const unsigned char *buf, int size)
{
  int i, c, n = 0;
  for (i = 0; i < size; i++)
  {
    n ^= (buf[i]<<8);
    for (c = 0; c < 8; c++)
      if (n & 0x8000)
	n = (n << 1) ^ 4129;
      else
	n = (n << 1);
  }
  return n & 0xffff;
}

Icon palette

The palette consists of 16 16-bit little endian integers, one for each
colour in the palette. Each integer consists of four four-bit fields:
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Alpha Red Green Blue

Alpha 15 is fully opaque, alpha 0 is fully transparent.

Icon bitmaps

The header should contain at least one icon bitmap for the file. If an
animated icon is desired, up to three bitmaps can be used (set the field
at offset $40 accordingly). The bitmaps are stored directly after each
other, starting at offset $80. The bitmaps contain one nybble per pixel.
Each byte thus represents two horizontally adjacent pixels, the high
nybble being the left one and the low nybble being the right one. Each
complete bitmap contains 1024 (32 * 32) nybbles, or 512 bytes.

Graphic eyecatch

The header can optionally contain a 72×56 pixel image shown as a graphic
eyecatch for the file in the DC boot ROM file manager. The graphic data
for the eyecatch is stored immediately after the last icon bitmap. There
are four possible visual modes, selected with the field at offset $44:
Mode Graphic data size (bytes) Data format
0 0 None
1 8064 16-bit true colour, see Icon palette for pixel format.
2 4544 (512 bytes palette, 4032 bytes bitmap) 256 colour palette based.
Begins with a palette in the same format as the Icon palette, but with
256 entries. Then the bitmap has one byte per pixel, giving the index
into the palette.
3 2048 (32 bytes palette, 2016 bytes bitmap) 16 colour palette based.
Format is just like the Icon palette and bitmap, except for the width
and height of the bitmap of course.

*/

typedef unsigned short uint16le;
typedef unsigned long  uint32le;

struct vmuheader {
	char desc_vm[16];
	char desc_dc[32];
	char application[16];
	uint16le n_icons;
	uint16le anime_speed;
	uint16le eyecache;
	uint16le crc;
	uint32le filesize;
	char reserved[20];
	uint16le icon_pal[16];
	unsigned char icon_data[32*32/2];
};

extern struct vmuheader vmuheader;

#endif