lib-font/src/opentype/tables/simple/variation/cvar.js

A JS based OpenType font inspector

import { SimpleTable } from "../../simple-table.js";
import lazy from "../../../../lazy.js";

/**
 * The OpenType `cvar` table.
 *
 * See https://docs.microsoft.com/en-us/typography/opentype/spec/cvar
 */
class cvar extends SimpleTable {
  constructor(dict, dataview) {
    const { p } = super(dict, dataview);
    this.majorVersion = uint16;
    this.minorVersion = uint16;
    this.tupleVariationCount = uint16;
    this.dataOffset = p.Offset32; // from the start of the table

    // FIXME: this is only correct if we can properly read full Tuple Variation Header...
    lazy(this`tupleVariationHeaders`, () =>
      [...new Array(this.tupleVariationCount)].map(
        (_) => new TupleVariationHeader(p)
      )
    );
  }
}

/**
 * See https://docs.microsoft.com/en-us/typography/opentype/spec/otvarcommonformats
 */
class TupleVariationHeader {
  constructor(p) {
    this.variationDataSize = p.uint16;

    // tupleIndex is a packed field:
    // - the high 4 bits are flags
    // - the low 12 bits are an index into a shared tuple records array.
    this.tupleIndex = p.uint16;

    // FIXME: not all tuples are actually there, it depends on the flags.

    this.peakTuple = new Tuple(p);
    this.intermediateStartTuple = new Tuple(p);
    this.intermediateEndTuple = new Tuple(p);
  }

  get EMBEDDED_PEAK_TUPLE() {
    return this.tupleIndex & (0x8000 === 0x8000);
  }
  get INTERMEDIATE_REGION() {
    return this.tupleIndex & (0x4000 === 0x4000);
  }
  get PRIVATE_POINT_NUMBERS() {
    return this.tupleIndex & (0x2000 === 0x2000);
  }
  get realTupleIndex() {
    return this.tupleIndex & 0xfff;
  }
}

class Tuple {
  constructor(p) {
    // FIXME: what... goes in here?
  }
}

export { cvar };