[XeTeX] Font protrusion --- new or old ?

[Peter Dyballa]

Am 07.02.2009 um 03:50 schrieb Nicolas Vaughan:

> However, after having examined several books and type specimens
> from the 16th to the 19th centuries (you can find them online in e.g.
> Archive.org), I have not been able to find any instances of font  
> protrusion.

Micro-typography has two levels. One is "character protrusion" which  
means that the characters at the left and at the right edges partly  
protrude into the margins. Usually you don't see it – that's the art!  
If you take a stripe of paper or a more precise mechanism and make it  
stand orthogonal to the lines and then move it to the text edges,  
then you'll see that the black of the glyphs does not stop at a  
thought line, not at once. Some glyphs, particularly punctuation and  
dashes, hang over into the margins. And also "regular" glyphs. The  
less black they have on the margin's side the more they can extend  
into the margin. This behaviour is based on tables. Humans built  
them, each for one font variant. You can extend this and build your own.

The second kind, which does not work with DVI output format, is kind  
of opposite of glue. Instead of manipulating the space between the  
glyphs that build a word – an ugly non-texnique of increasing it up  
to almost the width of whole character, mostly known from US DTP  
software – each glyph is manipulated. In one word they are either  
compressed or expanded by the same even factor. These are chosen in  
discrete steps of 2 %. Since this is equal for one word you can't  
easily see the change. If you have a large population of the same word 
(s) in a text and you measure each exactly, you might be able to see  
differences in their lengths.
In a first attempt this was accomplished by creating "new fonts" each  
with evenly compressed or expanded glyphs. Later pdfTeX learned to  
transform (as in PostScript via a matrix) the words. This could also  
be achieved in XeTeX I think ...

--
Greetings

   Pete

We have to expect it, otherwise we would be surprised.