[pdftex] Accessible LaTeX for large print (36pt-48pt) with reflow

Ulrike Fischer news3 at nililand.de
Fri Sep 16 10:08:23 CEST 2022

Am Tue, 13 Sep 2022 10:11:49 +1000 schrieb Ross Moore via pdftex:

I made a few reflow-tests with specially tailored enc-files and
various space chars.

> Han Thé Thành did this, by introducing a “fake space” that could be inserted either explicitly,
> or algorithmically if an appropriate flag was set.
> This space comes as the single character in a special font, set at an infinitesimal width
> so as to not upset the page rendering. 

The infinitesimal width is a major problem at least with acrobat. In
the cases where reflow worked acrobat adjusted the width of the
spaces to the width of the used space char. This means that the
space is there but infinitesimal small and so not visible. 

I think the code here must really be changed to get something
equivalent to "text\rlap{\pdffakespacechar} text" (without
disturbing hyphenation) with a space char which can be adjusted from
the macro layer so that font and size changing commands can adapt it
when needed. 

> • This works fine for PDF/A validation, but has *no effect* whatsoever for reflow.
> To achieve reflow one must satisfy the following:
>   A.  the space character needs to be included in the font subset written into the PDF;
>   B.  font characters must occur within the same text-strings as the words themselves.
> Otherwise no reflow can occur.

If the pdf is *tagged* reflow works with the
"text\rlap{\pdffakespacechar} text" approach even if the space char
is from a different font.

If the pdf is *untagged* it only works currently if the space char
is from the current font as acrobat looses it otherwise when
autotagging for the reflow, but I would say that is a bug in acrobat
and should be addressed there.

> Of course this all requires the current font to have a space character in the normal position in the font.
> Early TeX fonts do *not* meet this criterion; but more modern fonts (TeXGyre, etc.) and non-TeX fonts
> do have it. 

Even early type1 tex fonts have a space char, there is one in cmr
and in the ec fonts and I used them for the tests mentioned above.
The problem is that the space char is not encoded in T1-encoding and
most of the other encodings (imho it is only in LY1) so you can't
access it without changing the font. 

On the whole I doubt that it would be really feasible to change the
encodings to support the space char, so I think one should continue
to use a distinct font but address the width problem so that at
least tagged pdf works ok in a reflow  (tagged pdf is better anyway
as then acrobat doesn't have to guess the meaning of the text).

Ulrike Fischer 

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