Var store quantize

[behdad]

No description provided.

[behdad]

Not sure if we want to set quantization higher than one by default in any fontmake-related codepath.

[anthrotype]

why "round towards 0"?

you can use decimal.Decimal's quantize method with a ROUND_DOWN rounding method:

https://docs.python.org/3/library/decimal.html#decimal.ROUND_DOWN

though it might be quicker to simply do floor(v) if v > 0 else ceil(v)

[behdad]

I'll remove the comment. round is fine.

[behdad]

What I meant was a round that rounds .5 to 0, such that eg. with quantization 2, value 1 will become 0, not 2.

[anthrotype]

ah that's https://docs.python.org/3/library/decimal.html#decimal.ROUND_HALF_DOWN

[anthrotype]

yeah i think as a size saving optimization this quantization should make the deltas smaller, would be strange if it made them bigger

[anthrotype]

(though the sharing comes from reuse, not the delta magnitude itself)

[behdad]

Thanks!

[anthrotype]

Not sure if we want to set quantization higher than one by default in any fontmake-related codepath.

I don't know, maybe an option in the public varLib.build/build_many methods that ufo2ft uses. But I'm not sure if one wants to use the same quantization (if at all) for all the VarStores (HVAR, MVAR, COLR, etc.).
What did you have in mind for this? Make GPOS variable kerning tables smaller? Did somebody request this?

[anthrotype]

I think it's fine to have this option available in the fonttools varLib.varStore command-line tool only for now (that one only touches GDEF VarStore as used in GPOS), one can already start experiment with it and if needed we can surface it to varLib's public api

[behdad]

Did somebody request this?

No. I was just inspecting some varstores in GDEFs and saw many similar values. Ie. this is the entirety of the varstore from NotoSansCJK:

      <VarData index="0">
        <!-- ItemCount=118 -->
        <NumShorts value="0"/>
        <!-- VarRegionCount=1 -->
        <VarRegionIndex index="0" value="0"/>
        <Item index="0" value="[-113]"/>
        <Item index="1" value="[-93]"/>
        <Item index="2" value="[-91]"/>
        <Item index="3" value="[-90]"/>
        <Item index="4" value="[-88]"/>
        <Item index="5" value="[-84]"/>
        <Item index="6" value="[-83]"/>
        <Item index="7" value="[-73]"/>
        <Item index="8" value="[-71]"/>
        <Item index="9" value="[-69]"/>
        <Item index="10" value="[-68]"/>
        <Item index="11" value="[-66]"/>
        <Item index="12" value="[-65]"/>
        <Item index="13" value="[-62]"/>
        <Item index="14" value="[-61]"/>
        <Item index="15" value="[-58]"/>
        <Item index="16" value="[-57]"/>
        <Item index="17" value="[-56]"/>
        <Item index="18" value="[-52]"/>
        <Item index="19" value="[-51]"/>
        <Item index="20" value="[-50]"/>
        <Item index="21" value="[-49]"/>
        <Item index="22" value="[-48]"/>
        <Item index="23" value="[-47]"/>
        <Item index="24" value="[-46]"/>
        <Item index="25" value="[-45]"/>
        <Item index="26" value="[-44]"/>
        <Item index="27" value="[-43]"/>
        <Item index="28" value="[-42]"/>
        <Item index="29" value="[-41]"/>
        <Item index="30" value="[-40]"/>
        <Item index="31" value="[-39]"/>
        <Item index="32" value="[-38]"/>
        <Item index="33" value="[-37]"/>
        <Item index="34" value="[-36]"/>
        <Item index="35" value="[-34]"/>
        <Item index="36" value="[-33]"/>
        <Item index="37" value="[-32]"/>
        <Item index="38" value="[-31]"/>
        <Item index="39" value="[-30]"/>
        <Item index="40" value="[-29]"/>
        <Item index="41" value="[-28]"/>
        <Item index="42" value="[-27]"/>
        <Item index="43" value="[-26]"/>
        <Item index="44" value="[-25]"/>
        <Item index="45" value="[-24]"/>
        <Item index="46" value="[-23]"/>
        <Item index="47" value="[-22]"/>
        <Item index="48" value="[-21]"/>
        <Item index="49" value="[-20]"/>
        <Item index="50" value="[-19]"/>
        <Item index="51" value="[-18]"/>
        <Item index="52" value="[-17]"/>
        <Item index="53" value="[-16]"/>
        <Item index="54" value="[-15]"/>
        <Item index="55" value="[-14]"/>
        <Item index="56" value="[-13]"/>
        <Item index="57" value="[-12]"/>
        <Item index="58" value="[-11]"/>
        <Item index="59" value="[-10]"/>
        <Item index="60" value="[-9]"/>
        <Item index="61" value="[-8]"/>
        <Item index="62" value="[-7]"/>
        <Item index="63" value="[-6]"/>
        <Item index="64" value="[-5]"/>
        <Item index="65" value="[-4]"/>
        <Item index="66" value="[-3]"/>
        <Item index="67" value="[-2]"/>
        <Item index="68" value="[-1]"/>
        <Item index="69" value="[1]"/>
        <Item index="70" value="[2]"/>
        <Item index="71" value="[3]"/>
        <Item index="72" value="[4]"/>
        <Item index="73" value="[5]"/>
        <Item index="74" value="[6]"/>
        <Item index="75" value="[7]"/>
        <Item index="76" value="[8]"/>
        <Item index="77" value="[9]"/>
        <Item index="78" value="[10]"/>
        <Item index="79" value="[11]"/>
        <Item index="80" value="[12]"/>
        <Item index="81" value="[13]"/>
        <Item index="82" value="[14]"/>
        <Item index="83" value="[15]"/>
        <Item index="84" value="[16]"/>
        <Item index="85" value="[17]"/>
        <Item index="86" value="[18]"/>
        <Item index="87" value="[19]"/>
        <Item index="88" value="[20]"/>
        <Item index="89" value="[21]"/>
        <Item index="90" value="[22]"/>
        <Item index="91" value="[23]"/>
        <Item index="92" value="[26]"/>
        <Item index="93" value="[27]"/>
        <Item index="94" value="[28]"/>
        <Item index="95" value="[29]"/>
        <Item index="96" value="[30]"/>
        <Item index="97" value="[31]"/>
        <Item index="98" value="[33]"/>
        <Item index="99" value="[34]"/>
        <Item index="100" value="[35]"/>
        <Item index="101" value="[36]"/>
        <Item index="102" value="[37]"/>
        <Item index="103" value="[38]"/>
        <Item index="104" value="[39]"/>
        <Item index="105" value="[40]"/>
        <Item index="106" value="[41]"/>
        <Item index="107" value="[42]"/>
        <Item index="108" value="[43]"/>
        <Item index="109" value="[44]"/>
        <Item index="110" value="[46]"/>
        <Item index="111" value="[47]"/>
        <Item index="112" value="[49]"/>
        <Item index="113" value="[52]"/>
        <Item index="114" value="[55]"/>
        <Item index="115" value="[56]"/>
        <Item index="116" value="[66]"/>
        <Item index="117" value="[95]"/>
      </VarData>

[behdad]

I think it's fine to have this option available in the fonttools varLib.varStore command-line tool only for now (that one only touches GDEF VarStore as used in GPOS), one can already start experiment with it and if needed we can surface it to varLib's public api

Sounds good. Thanks.