[Scribus] some layout stability concerns from freetype kerning bug

[Michael Koren]

Hi,

Can upgrading external libraries affect the layout of text in existing
documents? I wanted to voice some concerns regarding layout consistency in
scribus documents prompted by my recent fun upgrading freetype. :)

For example, I came across an old debian bug report
(http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=351251) saying that
scribus and other programs no longer kerned truetype fonts with freetype
2.1.10. (It seems from the changelog and looking at the patch that truetype
kerning briefly got disabled in freetype, though that was fixed in debian as
of 2.1.10-2.) Since, as far as I can tell, scribus only stores the logical
text and high-level formatting in a document, changes in the font metrics
reported by freetype (even if they fix a prior bug) would change the
rendering of text in an existing file.

This is a problem because it could break a carefully constructed layout. I
don't know if other DTP programs have this issue as well, but in my opinion,
part of the point of using a layout app is precisely creating and preserving
document layout, which should include resilience to differences (and bugs)
in the environment in which a document is read. This particular case may be
uncommon, but there are other issues which could or do affect the stability
of existing layouts:

- opentype kerning: an earlier post said that scribus doesn't yet support
kerning of some opentype fonts. What happens to documents using them when it
does?
- font upgrades: are font version updates guaranteed to keep all the same
metrics? Otherwise font package upgrades could cause the same problem (this
also applies to sharing documents across platforms/distributions)
- scribus 1.2 and 1.3 have different algorithms for determining the spacing
above the first line of text in a frame, leading to layout changes on
scribus upgrades
- other changes to come in the 1.3.4+ new layout engine...

...etc. Some of these may seem picky, but again isn't precise control the
strength of DTP? Especially for long documents, subtle changes in text
rendering could cause undetected layout problems later in the document, such
as text overflowing the allotted space. There could likewise be problems
with tightly-fitted text no longer fitting in many small frames, which would
be tedious to fix. Do other people agree that this is important? Some
suggestions to address this:

- tracking versions of fonts used in documents, if this isn't done already
- storing the effective font metric information used to create a layout in
the document file
- storing the version of the layout algorithm used for text
- when a document is loaded, if any subsystem has been upgraded/differs from
the versions stored in the file, prompt to convert them or continue using
the original layout

Any other ideas?

Thanks,
Michael

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