awaforge

varInstance

AGPL-3.0-onlyRelease 2L4

Tuple scalars for gvar variation tuples and in-place application of decoded point deltas to a glyph (OT §10.6.2).

Module varInstance | Source packages/front/office/fonts/src/variable/instance.js | Deps fontErrors | Worker-safe yes

This module computes the scalar of a variation tuple at a normalised axis location and applies already-decoded gvar deltas, scaled by that scalar, to a glyph's points. It does not instantiate a font: there is no instantiate(font, coords) entry point, and decoding the tuples, selecting the deltas of each glyph and re-encoding the glyf data remain the caller's job.

Exports

Symbol Type Description
axisScalar function (peak: number, coord: number, intermStart?: number, intermEnd?: number) => number — scalar in [0, 1] for one axis. 1 when peak is 0 (axis unused) or coord === peak. With an explicit intermediate range: 0 outside [intermStart, intermEnd], otherwise a linear ramp up to the peak and back down. Without one: a triangle from 0 through peak, 0 when coord is on the other side of zero or at/beyond peak.
tupleScalar function (peak: number[], coord: number[], intermStart?: number[], intermEnd?: number[]) => number — product of the per-axis scalars, short-circuiting to 0 at the first zero. Throws a ContractError (code fonts/var-tuple-mismatch) when peak is missing or its length differs from coord.
applyGvarDeltas function (glyph: { points: { x, y, onCurve }[] }, deltas: { pointNumbers: number[], deltaX: number[], deltaY: number[] }, scalar: number) => void — adds delta * scalar to the point coordinates in place. An empty pointNumbers means every point (up to the shorter of deltaX.length and points.length); otherwise only the listed indices are touched, and out-of-range indices are skipped. Returns without effect when scalar is 0 or the glyph / deltas are missing.

Usage

import fw from '@awacloud/fw';
import { fw_require, modules } from '@awacloud/fonts';

for (const m of [...fw_require, ...modules]) fw.runtime.register(m);
const { tupleScalar, applyGvarDeltas } = fw.runtime.resolve('varInstance');

// One tuple over two axes, evaluated at a normalised location.
const scalar = tupleScalar([1, 0], [0.5, 0.25]); // 0.5 (second axis unused)

const glyph = { points: [{ x: 0, y: 0, onCurve: true }, { x: 100, y: 0, onCurve: true }] };
applyGvarDeltas(glyph, { pointNumbers: [], deltaX: [10, 20], deltaY: [0, 0] }, scalar);
// glyph.points[1].x === 110

Notes

  • Coordinates passed as coord are normalised values; build them with coordsConvert.
  • applyGvarDeltas mutates the glyph and does not interpolate untouched points (no inferred deltas for points absent from pointNumbers).
  • The deltas must already be unpacked, for example with the point-number and delta decoders exposed by gvar.

See also

  • coordsConvert — user-space values to normalised coordinates
  • gvar — glyph variation table and its packed-data decoders
  • errors — ContractError