FNT Font File Format

FNT is a simple binary font format used by Rockbox. It is a fixed-size raster font format that supports unicode.

(In this context a 'long' is intended to mean a 32 bit unit regardless of target architecture)

Header

The FNT header is exactly 36 bytes long consisting of the following fields:

Field	Length (bytes)	Description
UCHAR version[4]	4	magic number and version bytes (currently 'RB12')
USHORT maxwidth	2	font max width in pixels
USHORT height	2	font height in pixels
USHORT ascent	2	font ascent (baseline) in pixels
USHORT depth	2	monochrome (0) or anti-aliased (1)
ULONG firstchar	4	first character code in font
ULONG defaultchar	4	default character code in font
ULONG size	4	# characters in font
ULONG nbits	4	# bytes imagebits data in file
ULONG noffset	4	# longs offset data in file
ULONG nwidth	4	# bytes width data in file

Glyphs

Field	Length (bytes)	Description
MWIMAGEBITS bits	nbits	image bits variable data
[MWIMAGEBITS padded to 16-bit boundary]
USHORT offset	noffset*2	offset variable data
UCHAR width	nwidth*1	width variable data

(to be written)