NAME
lj4_font - groff fonts for use with devlj4
DESCRIPTION
Nominally, all Hewlett-Packard LaserJet 4–series and newer printers
have the same internal fonts: 45 scalable fonts and one bitmapped
Lineprinter font. The scalable fonts are available in sizes between
0.25 point and 999.75 points, in 0.25-point increments; the Lineprinter
font is available only in 8.5-point size.
The LaserJet font files included with groff assume that all printers
since the LaserJet 4 are identical. There are some differences between
fonts in the earlier and more recent printers, however. The LaserJet 4
printer used Agfa Intellifont technology for 35 of the internal
scalable fonts; the remaining 10 scalable fonts were TrueType.
Beginning with the LaserJet 4000–series printers introduced in 1997,
all scalable internal fonts have been TrueType. The number of
printable glyphs differs slightly between Intellifont and TrueType
fonts (generally, the TrueType fonts include more glyphs), and there
are some minor differences in glyph metrics. Differences among printer
models are described in the PCL 5 Comparison Guide and the PCL 5
Comparison Guide Addendum (for printers introduced since approximately
2001).
LaserJet printers reference a glyph by a combination of a 256-glyph
symbol set and an index within that symbol set. Many glyphs appear in
more than one symbol set; all combinations of symbol set and index that
reference the same glyph are equivalent. For each glyph, hpftodit(1)
searches a list of symbol sets, and selects the first set that contains
the glyph. The printing code generated by hpftodit(1) is an integer
that encodes a numerical value for the symbol set in the high byte(s),
and the index in the low byte. See groff_font(5) for a complete
description of the font file format; symbol sets are described in
greater detail in the PCL 5 Printer Language Technical Reference
Manual.
Two of the scalable fonts, Symbol and Wingdings, are bound to 256-glyph
symbol sets; the remaining scalable fonts, as well as the Lineprinter
font, support numerous symbol sets, sufficient to enable printing of
more than 600 glyphs.
The metrics generated by hpftodit(1) assume that the DESC file contains
values of 1200 for res and 6350 for unitwidth (or any combination
(e.g., 2400 and 3175) for which res × unitwidth = 7620000). Although
HP PCL 5 LaserJet printers support an internal resolution of 7200 units
per inch, they use a 16-bit signed integer for cursor positioning; if
devlj4 is to support U.S. ledger paper (11″ × 17″), the maximum usable
resolution is 32767 / 17, or 1927, units per inch, which rounds down to
1200 units per inch. If the largest required paper size is less (e.g.,
8.5″ × 11″ or A5), a greater resolution (and lesser unitwidth) can be
specified.
LIMITATIONS
Font metrics for Intellifont fonts were provided by Tagged Font Metric
(TFM) files originally developed by Agfa/Compugraphic. The TFM files
provided for these fonts supported 600+ glyphs and contained extensive
lists of kern pairs.
To accommodate developers who had become accustomed to TFM files, HP
also provided TFM files for the 10 TrueType fonts included in the
LaserJet 4. The TFM files for TrueType fonts generally included less
information than the Intellifont TFMs, supporting fewer glyphs, and in
most cases, providing no kerning information. By the time the
LaserJet 4000 printer was introduced, most developers had migrated to
other means of obtaining font metrics, and support for new TFM files
was very limited. The TFM files provided for the TrueType fonts in the
LaserJet 4000 support only the Latin 2 (ISO 8859-2) symbol set, and
include no kerning information; consequently, they are of little value
for any but the most rudimentary documents.
Because the Intellifont TFM files contain considerably more
information, they generally are preferable to the TrueType TFM files
even for use with the TrueType fonts in the newer printers. The
metrics for the TrueType fonts are very close, though not identical, to
those for the earlier Intellifont fonts of the same names. Although
most output using the Intellifont metrics with the newer printers is
quite acceptable, a few glyphs may fail to print as expected. The
differences in glyph metrics may be particularly noticeable with
composite parentheses, brackets, and braces used by eqn(1). A script,
located in /usr/share/groff/1.20.1/font/devlj4/generate, can be used to
adjust the metrics for these glyphs in the special font S for use with
printers that have all TrueType fonts.
At the time HP last supported TFM files, only Version 1 of the Unicode
standard was available. Consequently, many glyphs lacking assigned
code points were assigned by HP to the Private Use Area (PUA). Later
versions of the Unicode standard included code points outside the PUA
for many of these glyphs. The HP-supplied TrueType TFM files use the
PUA assignments; TFM files generated from more recent TrueType font
files require the later Unicode values to access the same glyphs.
Consequently, two different mapping files may be required: one for the
HP-supplied TFM files, and one for more recent TFM files.
FILES
/usr/share/groff/1.20.1/font/devlj4/DESC
Device description file.
/usr/share/groff/1.20.1/font/devlj4/F
Font description file for font F.
SEE ALSO
groff(1), groff_diff(1), hpftodit(1), grolj4(1), groff_font(5)