remove zero delta tuples from variable font

[aminabedi68]

Hi
in many projects and most of the time, a large number of glyphs remain unchanged along the axes, this cause to generate a large number of unnecessary zero delta tuples, like this:

      <tuple>
        <coord axis="wght" min="0.375" value="1.0" max="1.0"/>
        <coord axis="CNTR" value="1.0"/>
        <delta pt="0" x="0" y="0"/>
        <delta pt="1" x="0" y="0"/>
        <delta pt="2" x="0" y="0"/>
        <delta pt="3" x="0" y="0"/>
        <delta pt="4" x="0" y="0"/>
        <delta pt="5" x="0" y="0"/>
        <delta pt="6" x="0" y="0"/>
      </tuple>

removing these tuples helps to optimize the file size. glyphs app has Optimize Variable Delta for this, Slice also do similar optimization...

I need it as a part of independent build process. maybe it's predicted in fonttools or ttx, or a script(that i couldn't write it). so please help.
thank you.

(I'm not aware of software complexities, but extremely recommend to add it (directly or as an optional stage) to fontmake.)

[behdad]

Something like this should do:

from fontTools.ttLib import TTFont
import sys

font = TTFont(sys.argv[1])
gvar = font["gvar"]

new_variations = {}
for glyph,variations in gvar.variations.items():
    l1 = len(variations)
    variations = [v for v in variations
                  if any(i is None or i[0] or i[1]
                         for i in v.coordinates)]
    l2 = len(variations)
    if l1 != l2:
        print(glyph, l1, l2)
    if variations:
        new_variations[glyph] = variations
gvar.variations = new_variations

font.save("out.ttf")

[aminabedi68]

Wait. It looks like all of those correspond to composite glyphs. We encode those for a reason. There was a bug in CoreText I think...

If I change the snippet to only do the optimization for non-composite glyphs, then your font will be unchanged, suggesting that it was built with fontmake. Is that correct

yes.

[aminabedi68]

i tried again with your latest edition, it's working now :)
should i use it? i mean with the CoreText bug that you mentioned?

[behdad]

I'm coming up with a better fix in #2831 which has the CoreText workaround but is more optimized.

[behdad]

Can you build your font with fonttools from #2832 ?

[aminabedi68]

I'm sorry. Unfortunately I couldn't do it. I'm not familiar with this much about github.

[behdad]

(I'm not aware of software complexities, but extremely recommend to add it (directly or as an optional stage) to fontmake.)

We already do that:
https://github.com/fonttools/fonttools/blob/main/Lib/fontTools/varLib/__init__.py#L275

except for composite glyphs as I mentioned. The change that disabled this optimization for composites was:
9c3dde3

[aminabedi68]

ok, i didn't aware of that, thank you.