I start by limiting my observations to Linux, where I can analyse things more
thoroughly. My system: Linux Mint 17 64bit, with self compiled sources with
Qt Creator 3.1.2 and Qt lib 5.2.1. MuseScore built-in .ttf fonts are used as
they come in the current master.
I had the additional problem that Free Sans/Serif font is installed by
default on my distro and hides the font which comes with MuseScore. For
cleaner results, I removed the system font, but this might not be what the
average user wants to do (or *knows* how to do!): possibly another detail to
keep in mind.
A) By adding a staff text element and setting a specific font, I can notice
the following:
- Free Sans is NOT kerned;
- Free Serif IS kerned;
- MuseJazz IS kerned;
- all the 'standard' textual fonts I tried are kerned (by 'standard', I mean
textual fonts which either comes with my distro or I got from well-known
foundries, for instance Liberation, DejaVu, Droid, Gentium, Linux Libertine
and others. I ignored non-textual fonts, like dingbats or symbols).
____________________
B) *Notice*: care should be used in the string used for showing the kerning.
For instance, for the "Terj" string used by Marc as a test bed: in the Free
Serif/Sans, the digraph "Te" is kerned very little (-30 FU in Serif and -25
FU in Sans) and the offset is in many cases not easily noticeable. The
digraph "VA" is kerned significantly more: -70 FU in Serif and -60 FU in
Sans and should give more visible results.
Even more: "rj" is not kerned at all in Free Sans, but heavily kerned in
Serif (-70 FU).
In practice, a string like "VA" or "AV" should show rather evident kerning
for any font which has kerning data.
____________________
C) *Kerning tables* in .ttf fonts. If I open the current FreeSerif.ttf and
FreeSans.ttf fonts with FontForge, I notice that for both it raises a
warning:
"This font contains both a 'kern' table and a 'GPOS' table. The 'kern' table
will only be read if there is no 'kern' feature in 'GPOS'."
It looks like the fonts have been generated from the .sfd with the "Old
style kern" box checked.
Actually, after loading into FontForge the .ttf's, FreeSerif has kerning
data in GPOS for Latin, but FreeSans lacks such data (only has kerning for
Cyrillic).
By examining the lookup tables of the source FreeSans.sfd, it appears that
the GSUB kern table for Latin has no feature at all. By adding a 'kern'
feature for latn{dflt} to the kern lookup for Latin, re-generating the font
and re-compiling MuseScore, also the Free Sans is kerned.
For the font generation, I used the following options:
"Apple": OFF
"OpenType": ON
"Old style 'kern'": OFF
_________________________
D) About discrepancies between Windows and Mac (two systems I cannot work
with, as I no longer have machines running either), I simply want to remind
that Microsoft and Apple succeeded in making TTF and OTF specs a mess by
disagreeing in several details (kerning being one of them) and issuing
conflicting specs. Then I am not surprised that the same font may work
differently under Windows and under OSX but, as I said, I am not an expert
of these areas.
Anyway, we may have to accept the idea that different versions of the fonts
should be used under the two OSes.
____________________
E) About the advice in fonts/README.md to uncheck "Old style kern", I
originally put it in, because somebody (possibly Marc himself?) noticed
kerning issues under Windows with this box checked (this is also connected
with D) above).
I still believe that turning the "Old style 'kern'" on, may confuse some
font stack in some OS, but I will welcome reports of successful font
generation with this box turned ON.
Thanks,
Maurizio
--
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