fix(text): a variable font is instantiated out of a WOFF or a WOFF2, where the first weight off the file's default threw

[sidorares]

A variable font registered from a .woff2, which is how a web font nearly always arrives, threw from match at any weight but the file's default: ntk: cannot instantiate a variation of Geist-Regular (WOFF2). In react-x11-components' <Html> that was a whole document left blank, found on nextjs.org/blog. A .woff failed the same way.

Cause

fontkit 2.0.4's getVariation rebuilds the face as a plain sfnt from the container's bytes. For a WOFF that reads the wrong directory, and for a WOFF2 the bytes are still Brotli-compressed.

Fix

fontkit is now windowkit's fork, as a release tarball. The fix is windowkit/fontkit#1, offered upstream as foliojs/fontkit#389. Upstream's last release is from 2024, so dependencies names the URL of the tarball attached to the fork's v2.0.4-windowkit.1 release, which is what npm publish would have uploaded, and the lockfile holds its integrity. Not a github: spec: a git dependency has no dist/, npm builds one on every install with parcel and the devDependencies, 18 s measured, and Bun installs it unbuilt. The tarball was installed with npm and with Bun. AGENTS.md records the decision and when to go back to a range on npm.

One change in ntk itself. mendEmptyGlyphBoxes asked the loca table which glyphs are empty. A WOFF2 whose glyf table is transformed has no loca in the file, and fontkit reads the table after it in its place: it is wrong about 7 of the fixture's 76 glyphs, 24 of Geist's 975, 17 of KaTeX Main's 286. Those glyphs had their box read from a header that is not there, in static faces too, and in an instance of a variable face, whose box is needed to make the outline, the read went round until the stack ran out. A transformed glyf is now left alone.

The cannot instantiate error stays for an application that resolves fontkit to npm's over ntk's, and says that.

Tests

test/variable-fonts.test.js, with the fixture as a .woff and a .woff2, made from the .ttf with fontTools:

• an instance out of either container has every glyph of the sfnt's instance, by outline, advance and box, at three weights
• bytes registered with load and matched at 700 lay text out as wide as the sfnt does
• a WOFF2 glyph's box is its outline's, which fails on glyph 9 without the loca change

All three fail on master, and the first two fail with a stack overflow when only the fontkit is changed.

npm test: 1399 pass, 46 skipped, and one failure in present-clock.test.js, a frame-timing test that passed three times out of three alone, on a machine at a load average of 40.

Every character of Geist's variable WOFF2, 728 of them, was also set at five weights through <Html> with this ntk.