[texhax] TeX Queries (2): Artificial Break

Paul Isambert zappathustra at free.fr
Sat Jul 14 08:33:06 CEST 2012

Paul Stanley <paulrichardstanley at gmail.com> a écrit:
>  > Extract from TeXbook:
>  > "The `|\/|' tells \TeX\ to add an \break
>  > % makes the line tighter, to be fair
>  > ``{\sl^{italic correction}\/}'' to the previous letter, depending on
>  > that letter; this correction is about four times as much for an `$f$'
>  > as for a `$c$', in a typical italic font."
>  >
>  > What does the author mean by "makes the line tighter"?
> If the artificial break weren't there the line would be stretched too
> much; in other words, it's just a hand-made justification.
> Just to confirm, by "artificial break" are you refering to `\/' ?

Oh, no, I refer to \break, which is what the commented expression "makes
the line tighter, to be fair" also refers to. This has nothing to do
with what is being talked about here.

If I'm not mistaken, you're using a screen reader, and perhaps it got
things wrong here; what Don Knuth is saying is (removing macros):

    The `\/' tells TeX to add an ``italic correction'' to the previous
    letter ...

Then he adds \break after the word ``an'' so that TeX breaks the line
here instead of elsewhere, because TeX's default result here is not very
good. His remark about a tighter line comments on the use of \break, not
italic correction at all.

>  > What does "italic correction" actually mean?
> 		[snip]
> The italic correction adds a thin kern whose width depends on the
> preceding character; for instance, after an `f', it is much larger than
> after a `c', because in the former, the difference between the glyph's
> declared width and its real, visual width, i.e. its rightmost point,
> is much larger than in the latter. You can try this:
> Sorry, I'm not quite sure what you mean by the "declared" and "real" widths.

Well then I wasn't exactly crystal clear. Let's try again: the width
of a glyph is technically independent of the drawing of that glyph.
Suppose for instance that a glyph's rightmost point is at x-coordinate
50; then the glyph's width could very well be 52. What I have called
the ``real'' width is 50, and the ``declared'' width is 52; in other
words, all glyphs have a little bit of space on either side so that
adjacent glyphs don't touch.

For some glyphs, however, and italic glyphs in particular, especially an
italic ``f'', the declared width is smaller than the rightmost point; in
the above example, the declared width would be, say, 48; that means that
the glyph's right side hangs over the next glyph, which is generally
good, as long as the next glyph is in italic too; with an upright
parenthesis, things go wrong, hence italic correction.

I hope I've been clearer this time!


More information about the texhax mailing list