Lookuptype 6 tests #105
Comments
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substFormat 3 doesn't have additional function, it already parses everything in the constructor, as per https://github.com/Pomax/Font.js/blob/master/src/opentype/tables/advanced/shared/subtables/gsub.js#L281-L297, you can directly consult However, there is no coverage format 3. Only versions 1 and 2 exist, so that looks like a genuine bug. |
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Ah, I was thinking this referred to the Chained Sequence Context Format |
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Time to figure out why the CoverageTable format is so very wrong. Step one: does |
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Updating your code to include the lookup number and subtable format: ...
lookupIDs.forEach((id) => {
const lookup = GSUB.getLookup(id);
// Only dump lookup type 6 for DFLT/dflt
if (lookup.lookupType === 6 && lang === "dflt") {
console.log(`--- lookup type 6 in dflt, lookup ${id}`);
for (let i = 0; i < lookup.subTableCount; i++) {
const subtable = lookup.getSubTable(i);
console.log(` - subtable ${subtable.substFormat}`)
const coverage = subtable.getCoverageTable();
console.log(` `, coverage);
}
}
});
});
});
});
};so let's look at whether or not https://github.com/Pomax/lib-font/blob/master/src/opentype/tables/advanced/shared/subtables/gsub.js#L281-L299 is doing the right thing: if (this.substFormat === 3) {
this.backtrackGlyphCount = p.uint16;
this.backtrackCoverageOffsets = [
...new Array(this.backtrackGlyphCount),
].map((_) => p.Offset16);
this.inputGlyphCount = p.uint16;
this.inputCoverageOffsets = [...new Array(this.inputGlyphCount)].map(
(_) => p.Offset16
);
this.lookaheadGlyphCount = p.uint16;
this.lookaheadCoverageOffsets = [
...new Array(this.lookaheadGlyphCount),
].map((_) => p.Offset16);
this.substitutionCount = p.uint16;
this.substLookupRecords = [...new Array(this.substitutionCount)].map(
(_) => new SubstLookupRecord(p)
);
}This should match https://docs.microsoft.com/en-us/typography/opentype/spec/chapter2#chseqctxt3:
The class LookupType extends ParsedData {
constructor(p) {
super(p);
this.substFormat = p.uint16;
this.coverageOffset = p.Offset16;
}
getCoverageTable() {
let p = this.parser;
p.currentPosition = this.start + this.coverageOffset;
return new CoverageTable(p);
}
}But we actually see this reading too much data. For substformat 3, the near universal LookupType 5, subtable format 3 is the only other data structure that does this, and has code in place to correct for reading ahead by two bytes, but LookupType 6 subtable format 3 does not: let's fix that. Adding the same correction: p.currentPosition -= 2;
delete this.coverageOffset;now yields: So that looks pretty good @RoelN |
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This seems to report |
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Further updating: the 6.3 code was not complete, so I've updated that in 2ae18d9 and I've updated my test run code to: import { Font } from "./lib-font.js";
const font = new Font("boink");
font.src = `./fonts/Recursive_VF_1.064.ttf`;
// font.src = `./fonts/MehrNastaliqWeb-Regular.ttf`;
font.onload = (evt) => {
let font = evt.detail.font;
const { GSUB } = font.opentype.tables;
let scripts = GSUB.getSupportedScripts();
scripts.forEach((script) => {
let langsys = GSUB.getSupportedLangSys(script);
langsys.forEach((lang) => {
let langSysTable = GSUB.getLangSysTable(script, lang);
let features = GSUB.getFeatures(langSysTable);
features.forEach((feature) => {
const lookupIDs = feature.lookupListIndices;
lookupIDs.forEach((id) => {
const lookup = GSUB.getLookup(id);
// Only dump lookup type 6 for DFLT/dflt
if (lookup.lookupType === 6 && lang === "dflt") {
for(let i=0; i<lookup.subTableCount; i++) {
let subtable = lookup.getSubTable(i);
console.log(`=====================================================`);
console.log(`lookup type 6 in dflt, lookup ${id}, subtable ${i}`);
console.log(`=====================================================`);
if (subtable.backtrackGlyphCount > 0)
subtable.backtrackCoverageOffsets.forEach((offset, id) => {
let coverage = subtable.getCoverageFromOffset(offset);
console.log(`backtrack coverage ${id+1}:`, coverage);
});
if (subtable.lookaheadGlyphCount > 0)
subtable.lookaheadCoverageOffsets.forEach((offset, id) => {
let coverage = subtable.getCoverageFromOffset(offset);
console.log(`lookahead coverage ${id+1}:`, coverage);
});
subtable.seqLookupRecords.forEach(slRecord => {
console.log(`sequence lookup record:`, slRecord);
});
}
}
});
});
});
});
};Which yields an insane amount of data, but of the form: Which looks more in line with what the data should look like. the first backtrack rule maps to: Which anecdotally feels like things make more sense now =) Confirming with TTX shows: <Lookup index="1">
<LookupType value="6"/>
<LookupFlag value="0"/>
<!-- SubTableCount=23 -->
<ChainContextSubst index="0" Format="3">
<!-- BacktrackGlyphCount=11 -->
<BacktrackCoverage index="0" Format="2">
<Glyph value="zero"/>
<Glyph value="one"/>
<Glyph value="two"/>
<Glyph value="three"/>
<Glyph value="four"/>
<Glyph value="five"/>
<Glyph value="six"/>
<Glyph value="seven"/>
<Glyph value="eight"/>
<Glyph value="nine"/>
<Glyph value="zero.sans"/>
</BacktrackCoverage>
<BacktrackCoverage index="1" Format="2">
<Glyph value="zero"/>
<Glyph value="one"/>
<Glyph value="two"/>
<Glyph value="three"/>
<Glyph value="four"/>
<Glyph value="five"/>
<Glyph value="six"/>
<Glyph value="seven"/>
<Glyph value="eight"/>
<Glyph value="nine"/>
<Glyph value="zero.sans"/>
</BacktrackCoverage> |
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This is fantastic! Thanks a lot, @Pomax! For the record, I'm also logging the input coverage, so you have a complete picture of what goes "in" the substitution: if (subtable.inputGlyphCount > 0)
subtable.inputCoverageOffsets.forEach((offset, id) => {
let coverage = subtable.getCoverageFromOffset(offset);
console.log(`input coverage ${id+1}:`, coverage);
console.log("\n");
}); |
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I'm testing as follows:
For Recusive, this outputs stuff like:
Which seems wrong.
If I understand https://github.com/Pomax/Font.js/blob/master/src/opentype/tables/advanced/shared/subtables/gsub.js#L301 correctly there's only getters for
substFormat1 and 2, while most fonts I test with have asubstFormatof 3.Dumping the subtable appears to provide valid data, if these offsets are supposed to jump around this much (from 1 to 1410, to 1, to 20, etc.)
Getting
backtrackCoverage,inputCoverageandlookaheadCoveragewith a list of glyphs sounds like what I could use for Wakamai Fondue. Is there a way to get to that?The text was updated successfully, but these errors were encountered: