[scribus] right-alignment bug

[ZASKE Martin]

Dear list and Scribus bug-fixers,

below I will paste an extract from my correspondence with a friend from
my organization (we do not know each other face to face), who managed to
create a test-font (as a tiny modification of another font which is
affected), which does NOT trigger the right-align bug any longer.

So what he has got to say, might be relevant for this bug. I paste it
here for the list, so that one or two other users can have their say,
before it gets summarized and submitted to "the people in the engine
room" (who got my utmost respect). Maybe JLuc would know how to submit
such information, or do I just paste it as another "note" at the
bug-tracking site? Will it be found there?




---- Here some extracts from our exchange: ----

On 2014-05-21 at 15:28 Martin Zaske wrote:
> Hi Bob,
>
> I am really exited about your suspicion. Of course I am willing to
test since we are benefiting from your help. .......
> Whatever you tweaked in the copy of Charis, it makes the right-align
bug in Scribus "go away".

That's good news!

> Normally (with the bug) each right-aligned line shows one unwanted
right-side-space (except the very last line). With your modified version
it behaves better. ......
>
> Now I would like to ask you "how you did it", please. Maybe you could
briefly write up your tweak in "font-developer-speak", so that I can
post it on the Scribus list and on the Scribus bug-management-site, for
the benefit of the Scribus users, and developers and other font makers.

My suspicions are that Scribus is "drawing" the glyphs not only for the
text of your lines, but also at least the "carriage return" character
(U+000D) and possibly the "linefeed" character (U+000A). Most
applications don't actually draw these characters (unless the user turns
on special "show invisible" or similar options that the app might
support) but rather just performs the necessary re-positioning that
would be indicated by the CR or LF.

Actually drawing the CR/LF characters wouldn't be a problem -- UNLESS
the font being rendered had real glyphs encoded to the CR or LF
characters. As it turns out, Charis and Andika (and a number of other of
our fonts) *do* have a glyph encoded for the CR character. This isn't a
violation of any technical specification, and it hasn't (until now) been
a problem.

Thus my guess is that all the fonts you are having trouble with have a
glyph encoded for the CR and/or LF characters and the fonts that "work"
do not encode those.

What I tweaked in the font I sent  you was to remove the CR character
from the font (LF wasn't present anyway).

> Would you consider this an issue which should rather be "fixed" at the
font-side of things, or rather at the text-rendering (in Scribus) side
of things?

As you might deduce from the above description, I think it could be
"fixed" either way. One could change Scribus so that it doesn't
physically draw the CR/LF glyphs, or one can patch all the affected
fonts so they don't encode those characters.

Assuming my understanding is correct, then making the change to Scribus
would be a universal fix. But there may be reasons that the Scribus
folks don't want to make this change, in which case you are dependent on
font vendors to fix all the fonts that you are interested in.

Hope this helps
Bob

---- end of extract ----

So, we got more information now. And as this goes beyond my level, I
would like to hear from people who know about the Scribus text rendering
engine: Are we on the right track?

fwiw,

Martin