Stonebrook Quill

Strokes to outlines

Nothing here was drawn as an outline. Every letter in the engine is a set of pen strokes: a skeleton path, the angle of the nib, how hard it presses. The exporter (crates/letter/examples/fontgen.rs) asks the engine for each form as the nib swept along its strokes, in one particular writing, with the hand's small differences of slant, proportion and placing. It takes the union of those pieces (i_overlay) and fits the outline with smooth curves: cubic least squares, kept to within about half a font unit of the ink and split at the true corners, then converted to the quadratic curves of TrueType (kurbo).

Where a letter has fewer than three shapes, the exporter writes its canonical form again with a different seed. These further writings (a.w1, a.w2) are the same letter with the hand's small irregularities, and they give the contextual rotation enough shapes to choose from.

Spacing and kerning

Spacing comes from the engine's optical spacing: for every ordered pair of forms it reports how far apart it would set them. That is split into a right side for the first and a left side for the second (a median polish over the lower case; capitals are judged after capitals, figures after figures), which become the advance widths and side bearings. What is left over is the kerning, grouped into classes.

Tables and features

The features are generated as an Adobe feature file and compiled with fea-rs; the other tables are built with write-fonts. Everything is read from the engine, so new forms and joins appear in the fonts when they are regenerated, and the output is deterministic.

This page reads the finished font files back (crates/letter/examples/fontdata.rs, with ttf-parser) and checks each form it shows by shaping it with rustybuzz, the Rust port of the shaper Chrome and Firefox use.