[XeTeX] XeTeX, fontspec, OTF, and fontdimens

[mskala at ansuz.sooke.bc.ca]

On Sun, 27 Feb 2011, Tobias Schoel wrote:
> If the monospace option is set by hand for non-monospaced fonts, how will the
> letters be positioned in the monospaced grid? How should the following pattern
> look?

I only envision the monospace option as affecting the width of TeX's word
and sentence spaces - that is, \fontdimen2, 3, 4, and 7.  It wouldn't
affect other font metrics.  Glyphs would still be set in the widths
specified by font; and if those widths happened to be proportional, then
there wouldn't BE a monospaced grid; "mim" would probably be narrower
than "mmm".

It's important not to override the widths of glyphs because of the common
case I described earlier of a font that is in some meaningful way
monospaced, but doesn't have all characters exactly the same width.  For
instance, fonts designed for CJK typesetting may have all the Latin
characters the same width, and all the CJK characters exactly twice that
width.  These two lines should be the same width, equal to eight
typewriter spaces, despite being six glyphs and two spaces on the first
line and just four glyphs on the second line:

ab cd ef
なになに

(and they do line up in the terminal window where I'm typing this)

Is that monospace?  Well, the spaces between words and sentences
in Latin script should be treated as they would for a monospace font; if
they are, then there will be a grid structure to the page; but the glyphs
are not all the same width.

If someone wants to force a proportional font to be typeset as monospace
with the glyphs on a grid, I think that's beyond the scope of what XeTeX
should support.  Such users would be better served by editing the font
files before giving them to TeX, and in that case they can make their own
decisions about how to deal with the "Where is the glyph within the box?"
issue when they do the editing.
-- 
Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before principles.
http://ansuz.sooke.bc.ca/