[texhax] TeX Queries (2): Artificial Break

Paul Isambert zappathustra at free.fr
Wed Jul 18 07:47:25 CEST 2012

Paul Stanley <paulrichardstanley at gmail.com> a écrit:
> Are descenders glyphs that *descend* below the baseline?

Parts of glyphs, yes.

> Just to confirm, does kerning concerns both the adding and 
> subtracting from the advanced width of the glyph?

Visually, yes; technically, as far as TeX is concerned, no: it is the
adding of space, possibly negative.

> Could you please elaborate why many more kerning pairs would be 
> needed?  I'm not sure if i understand the problem.

An italic `f', for instance, crosses the baseline at x = 20, and then
moves upwards and to the right, so that it ends at x = 50. If its width
were equivalent to its rightmost point, then an `o' next to it would
be placed at x = 50. Thus there would be a gap of 30 units between the
base of the `f' and the base of the `o', and that gap would give the
impression that the letters are disconnected, and you'd need kerning.
However, since that is going to happen with all letters following an
italic `f', it's simpler to set the width of that glyph to something
less than 50 so that following glyphs are correctly placed without
additional kerning.

> yes, kerning pairs can be an accessibility pain in the ... They are 
> either invisible to the screen reader or show up as strange control 
> characters (which comes to the same thing).

In a PDF, kerning is not denoted differently from interword space; as
far as I can tell from text extraction (searching for a string), a space
is interpreted as such if it doesn't exceed a certain amount. For
instance, with:

    ab\kern1pt cd
    ab\kern2pt cd

both Acrobat and Evince identify ``abcd'' in the first case but not in
the second (I haven't looked up the PDF reference to see whether that's
expected behavior).


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