Re: [Groff] Devps unmatched metrics

[Gunnar Ritter]

Tadziu Hoffmann <address@hidden> wrote:

> The kerning information, however, can be modified without
> a new font being created, because it is something the font
> doesn't "know" about.  [Don't know what the situation is with
> OpenType.]

Principally the same, in that the kerning information is not
sent to the output device.

A CFF-based OpenType font is essentially a PostScript font
(in a different encoding than Type 1) wrapped in a TrueType
font file. The output device only sees the PostScript part,
not the TrueType part that contains the kerning information
(in the GPOS table).

A TrueType font contains the kerning information in the kern
table which is not typically included when encoding the glyph
data for the output device as Type 42.

However, since the kerning information is contained in the
same input file, modifying it directly (as can easily be done
with AFM) is not advisable. It is absolutely no problem to
introduce different kerning values by other means, though.

> Groff runs out of the box on a multitude of different machines
> and operating systems without requiring the font files at all
> (only the metrics), and groff does not need ghostscript to work.
> (Of course we all use ghostscript, but it's still optional.)
> I prefer the default installation of groff to remain that way.

Another point is that if metrics differ between installed
systems, the generated documents (read: their PostScript
texts) also vary between them. Although the troff world has
not been as strict on avoiding this as Knuth, making it the
default situation would be highly undesirable.

Gunnar