[XeTeX] fontsizes and interlinear space

[Jonathan Kew]

On 22 Aug 2006, at 6:01 pm, Pablo Rodríguez wrote:

>>> Using XeLaTeX, I experience something that I have never  
>>> experienced in
>>> LaTeX (as far as I can remember). Paragraphs do have different
>>> interlinear spaces within the same paragraph.

Standard LaTeX will do this too, if you use glyphs (or accents) that  
cause the lines to be high/deep enough that they would otherwise  
clash. But the CM fonts and standard LaTeX styles, at least, are  
designed such that accented capitals don't normally cause this.

>>> Probably this is caused by a flawed font design (('m using GFS  
>>> Didot),
>>> but I wonder whether there is a way to fix this with XeTeX.

I wouldn't call it flawed; there are a number of factors that  
interact here, of which font design is one.

>>
>> Maybe, maybe not.
>> You'll need to be more precise; can you post a minimal example of a
>> paragraph that does this?
>
> Thanks for the answer, Will.
>
> I'm not sure, but I think that XeLaTeX (or whatever it might be) seems
> not to get the font size from the ascent and descent (which is  
> common to
> all glyphs), but from the actual glyph.

Indeed it does. It didn't, in earlier versions, but users often  
requested this, and it was finally implemented in release 0.993 (June).

You can switch to the earlier behavior, if you really want, by  
setting \XeTeXuseglyphmetrics=0 in your document.

However, this will that if a font has tall glyphs (e.g., accented  
capitals) that extend beyond the nominal ascent, they may clash with  
descenders from the line above. With a little forcing of where line- 
breaks occur, you can see this just about happening with your sample  
text; try this version:

\documentclass[a4paper,12pt]{article}
\usepackage[spanish]{babel}
\usepackage{fontspec,xunicode,xltxtra}
\XeTeXuseglyphmetrics=0

\setromanfont{GFS Didot}
\begin{document}
\begin{quote}
De manera especialísima se advierte en el discípulo de Platón la
insatisfacción que le producen las tentativas de su maestro y la
determinación que le lleva a intentar dar una respuesta al inquietante
problema, a la oscura cuestión del no-ser.~Ése,~aunque~formulado ahora
de forma insuficiente, pudo ser el reto de Aristóteles. Ésa es, al
menos, una de las formas en que se puede leer el texto de
\emph{filosofía primera} de Aristóteles.
\end{quote}
\end{document}

Note the "p" of respuesta and the "É" on the following line; and  
compare the result without \XeTeXuseglyphmetrics=0.

What you might want to do is set the line spacing slightly wider than  
LaTeX's default, if you're using a font like this, so that the lines  
are always spaced sufficiently to allow accented uppercase letters  
without the risk of clashes. For example, rather than 12pt text on  
14.5pt leading, you might want to use 12/15.5 or even 12/16pt. (I'm  
sure the experienced LaTeX users here can tell you an easy way to set  
this.)

JK