Optional param to only diff mark combos which shaping engines allow

googlefonts / fontdiffenator

Font comparison tool

Apache License 2.0

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Optional param to only diff mark combos which shaping engines allow #7

Closed m4rc1e closed 6 years ago

m4rc1e commented 6 years ago

Since each font builder has their own way of building GPOS mark features, I'm tempted to only diff combos which shaping engines allow.

anthrotype commented 6 years ago

what are these "combos which shaping engines allow"?

m4rc1e commented 6 years ago

@anthrotype I assumed that shaping engines could only add Nonspacing marks to certain base glyphs... I'm wrong.

screen shot 2018-06-19 at 13 16 47

m4rc1e commented 6 years ago

Interestingly in Mac OS X, it will position glyphs which are not Nonspacing Marks as well.

screen shot 2018-06-19 at 14 01 00

screen shot 2018-06-19 at 14 13 11 D positioned with acute (U+00B4)

screen shot 2018-06-19 at 14 16 00 Font with no anchor on acute (U+00B4)

anthrotype commented 6 years ago

check that font's GDEF table, and see if the "acute" glyph is marked as class 3 (combining mark)

m4rc1e commented 6 years ago

Nope

<Glyph value="acute"/>

Alice-Regular.txt

anthrotype commented 6 years ago

Ok it’s not marked as such, but still it is included in the Coverage table of the mark class for all the top marks, along with acutcomb etc so for the sake of the mark feature it is a combining mark

anthrotype commented 6 years ago

The GDEF category applies for things like IgnoreMarks lookup flags