[XeTeX] letter spacing

Jonathan Kew jonathan_kew at sil.org
Sun Jun 4 15:18:58 CEST 2006

On 4 Jun 2006, at 1:34 pm, Adam Twardoch wrote:

> Jonathan Kew wrote:
>> I'd usually agree with those who consider letterspacing a Bad Thing,
> No no no. Letterspacing of lowercase is generally considered a Bad  
> Thing.

Yes, sorry, this statement was much too general; adjustments for all- 
caps setting are indeed often appropriate.

> I don't know much about TeX and am now actually quite surprised to  
> hear
> that there is no standard tracking control in TeX. Tracking is an
> essential ingredient of typographic design. Good typographic design
> usually involves adding and removing some interletter whitespace
> depending on the point size. Especially when using a font that doesn't
> have independent optical masters, you'd slightly increase tracking in
> small sizes and slightly reduce it in large sizes. This has always  
> been
> a common practice.

Yes. The traditional TeX view is that fonts should be designed  
specifically for the size, not just scaled linearly, so Knuth  
wouldn't have needed to adjust tracking for this reason; it would be  
built into the fonts. Thus, I expect cmr7 has relatively more  
interletter space than cmr17. But with the adoption of scalable fonts  
(most of which don't have optical sizes), it becomes an issue.

It would be possible to vary the tracking of a (single-design)  
scalable font by the use of TeX virtual fonts, so that there would be  
multiple TFMs and VFs for use at different sizes, even though the  
actual glyph outlines would be the same. I don't know whether this  
has actually been done in some of the traditional LaTeX font  
packages; probably others here would know more.

The XeTeX approach starts with the assumption that the font designer  
was right, so we use the font as designed. If there are optical  
sizes, we automatically use them. But of course there are times when  
(especially in the absence of optical sizes, but also sometimes for  
other reasons) it would be beneficial to adjust tracking. I'd  
definitely like to provide access to the AAT tracking table, when  
available; and in addition, provide a "pseudo-feature" to impose  
adjustments on glyph spacing in any font. Just hasn't gotten done  


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