CHAPTER 4
TrueType Fonts
Downloading TrueType Fonts to Disk 79
operation of intelligent font downloaders, there are several conventions that must be
used for the textual definition of the font.
The first line in the PostScript font file is
%!PS-TrueTypeFont-sfntFormat-fontRevision-commentFormat
where sfntFormat is the version number of the 'sfnt' format (from the 'sfnt' header),
fontRevision is the font manufacturer’s revision of the font (also from the 'sfnt'
header), and commentFormat refers to this version of the commenting convention. An
intelligent downloading utility can use this line to identify TrueType fonts on a printer’s
hard disk.
If this line appears as the first line of a font program, the following conventions must be
strictly followed or an error may occur.
■ The token /sfnts must be followed by the token [ and either < or (, depending on
the encoding of the binary 'sfnt' data. There may be whitespace and/or control
characters (<CR>, <LF>, <TAB>) between these tokens.
■ All of the strings defined in the 'sfnt' array of a font program must use the same
encoding (ASCII or ASCIIHex). Different font programs may use different encodings.
■ The characters representing the 'sfnt' data must follow a sequence of N characters
of data followed by M characters of whitespace, repeating until the string’s data is
exhausted. The last sequence of character data may be less than N characters long.
The last tokens in each string should be M characters of whitespace, followed by the
character(s) for 1 pad byte of data, followed immediately by the string terminator
(either > or), depending on the data encoding. There may be whitespace and/or
control characters between string definitions. The values of M and N must be
constants for a font program. Different font programs may use different values of M
and N. The value for N must be between 0 and 2048, inclusive.
Note
The 1024 bytes of binary 'sfnt' data require 2048 characters to
represent them in the ASCII Hex encoding. ◆
■ The last string definition in the 'sfnt' array must be followed by the token ] and the
token def. There may be whitespace or control characters, or a combination of
whitespace and control characters, between these tokens.
■ The PostScript code for different classes of printers must be bracketed with begin
and end comments. The end comments are already used by the checkload and
fcheckload procedures when discarding sections of PostScript code that are not
appropriate for a given class of printer. The begin comments are for the font
downloader, which does not have a PostScript interpreter to do the discarding
automatically. Because of a limitation in the readline operator in early versions of the
PostScript interpreter, the end comments must be bracketed by only linefeed (ASCII
10) characters.
