Ok, let's use the big guns...
I run ttx on the current MuseScore FreeXxxx.ttf fonts and on your Mac and
non-Mac variants (downloaded from your github PR). Leaving aside for the
moment being the bold variants, these are the results.
*1) Common tables*: All fonts contains the following tables (which are more
or less mandatory):
'GlyphOrder'
'head'
'hhea'
'maxp'
'OS/2'
'hmtx'
'cmap'
'cvt '
'loca'
'glyf'
'name'
'post'
'gasp'
'FFTM'
*2) The current MuseScore fonts* in addition contain:
*) FreeSans.ttf Tables:
'fpgm'
'prep'
'kern' for Cyrillic only
'GDEF'
'GPOS' kern for Cyrillic, Latin and 'bn'(?), but only Cyrillic
is linked
to main lookup table
'GSUB'
*) FreeSerif.ttf Tables:
'fpgm'
'prep'
'kern' for Cyrillic and Latin (and several others)
'GDEF'
'GPOS' kern for Arabic, Cyrillic, Devanagari, Latin, Thai all
properly
linked
'GSUB'
Note that:
2.1) *both* 'kern' *and* 'GPOS'/'kern' are present
2.2) 'GPOS'/'kern' for FreeSans.ttf is bogus; in fact FreeSans.ttf lacks any
usable kerning data for Latin.
2.1) is in general not good, as the presence of both tables may confuse some
font stack and/or make unpredictable which table a given font stack will
use. The cure for this is to have *only one* of the 'OpenType' and
'Old-style kern' check boxes checked at a time.
2.2) is also obviously not good! There is a cure for this which I gave in my
previous post and will repeat below.
*3) Your font variants* in addition to the common tables also contain:
*) FreeSans.ttf Tables:
'kern' for Latin only
*) FreeSans-Mac tables:
'GDEF'
'GPOS' kern for Latin only
'GSUB'
*) FreeSerif.ttf Tables:
'kern' for Latin only
*) FreeSerif-Mac.ttf Tables:
'GDEF'
'GPOS' kern for Latin only
'GSUB'
Note that:
3.1) non-Mac versions have the 'kern' table and lack the OpenType tables (as
you turned off the OpenType check box) and that Mac versions have the
OpenType tables and lack the 'kern' table (as you turned on the OpenTypeType
check box and possibly kept off the Old-style kern check box). Having only
one of the two tables is generally positive, as I said above.
3.2) Having different sets of tables for different fonts is sub-optimal, as
it complicates maintenance and development and might be a source of problems
difficult to track. My opinion is that there should a very good reason for
this.
3.3) All fonts lost the non-Latin kern data. This may be secondary right
now, but has to be kept in mind, given the international coverage of
MuseScore. It would be nice to know from which editing / choice of settings
this happened.
3.4) All fonts lack the 'fpgm' and 'prep' tables. They are not related with
kern (at least, they should not be), but with font instructing: loosing
these tables is generally not good, as very few (and usually rather simple)
fonts can have instructing without them. We probably do not want to loose
them.
__________________________
*4) Some conclusions?*
4.1) Of the two possibilities surfaced above:
'kern' table only without 'GPOS'/'kern'
vs.
'GPOS'/'kern' (and in general OpenType) tables only without the 'kern'
table,
I believe the latter is generally preferable, because the former is a rather
outdated setup and because other OpenType tables may contain useful data;
for instance the FreeType-based font stack in (most) Linux automatically
recognizes the 'GSUB'/'liga' sub-table for ligature substitution.
4.2) Of course, this implies that data in OpenType tables are correct. In
current MuseScore FreeSans.sfd font, 'GPOS'/'kern' data are inconsistent,
this is why it does not behave correctly.
4.3) Fixing FreeSans.sfd is easy: it is enough to add the missing 'kern'
feature in the 'GPOS'/'kern' sub-table. With this change, the rebellious
"VA" pair -- among others -- kerns correctly!
4.4) IMHO, until something solid surfaces against, the way to go is to
generate all fonts from FontForge with:
*) Correct table data!
*) "OpenType" turned ON
*) "Old-style kern" turned OFF
*) "TrueType hints" turned ON
in order to have 'GPOS'/'kern' sub-table (and other potentially useful
OpenType tables) without the 'kern' table messing in.
If helpful, I can submit a PR along 4.3) and 4.4) guidelines. If this would
be more messy than helpful, I'll happily leave it to someone else.
4.5) For Mac/OSX, the impact of the "Apple" generation option possibly
requires some investigation. I cannot do that; if someone is willing, is
welcome! I would start with the options listed above, though.
Hoping it helps...
Maurizio
--
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