CrossGlyph

Tune a font for an Xteink reader running CrossPoint, and watch the page redraw as you move each control. Changes appear as fast as your machine can rebuild that part of the font, which is fast enough to keep turning a knob and watching what happens.

These readers draw in four shades of grey and nothing else, so most fonts need work before they read well on one. Without a preview, every guess costs a card swap or an emulator run, which is why most people stop at the point size.

• The reader's own renderer. The firmware's drawing code, compiled to run in the browser, so the page shows what the device will draw and not an impression of it.
• Controls for the letters. How dark the type is (gamma, and the three grey cut points), how thick or thin the strokes are (weight, and stem darkening), a slant for a face with no italic of its own, how the outline is snapped onto the pixel grid (hinting, grayscale hinting, and a one-bit mode that drops the greys), the space between letters, words and lines, how hard pairs are pulled together (kerning), whether fi joins into one shape (ligatures), and whether digits are all one width. docs/fonts.md explains what every one of them does to the type.
• Controls for the page. Margins, alignment, line and paragraph spacing, hyphenation and the language its rules come from, anti-aliasing and night mode, so the page you are judging is set up like the device you are judging it for.
• The page inside the reader. Drawn from XTEINK's own models, one screen pixel to one of your monitor's, shaded to match a real device and adjustable from there. One press copies it out as an image.
• Variable fonts. These carry a range of weights in a single file. Build one at the weight its designer named, or at any weight you pick. Left alone, Merriweather would hand you its Light as your Regular.
• A family in seconds. Regular, bold, italic and bold italic, at every point size you asked for, one process per size.
• The bundled Noto faces on request, so a missing arrow or Greek letter is not a hole in the page. Each one lends its own bold or italic to text set that way, where it has one.
• Arabic comes out joined with any face. A modern Arabic font carries the rules for how letters connect, and CrossGlyph runs them and builds the joined shapes in. The device has no room to do that itself.
• Nothing installed system wide. The launcher fetches uv, Python and the dependencies into a cache directory you can delete.

CrossGlyph turns TTF and OTF files into .cpfont, the format the device reads. A .cpfont holds a picture of every letter at one point size, in the four greys the screen has, along with the tables that space letter pairs and join fi into one shape. The device cannot scale type itself, so each point size is a separate file and a separate build.

Quick start

1. Unpack the release somewhere you can write to.
2. Run crossglyph.cmd on Windows, or ./crossglyph.sh on macOS and Linux.
3. Put your TTF or OTF files in the fonts folder beside the launcher.

The launcher fetches uv on first use, which then fetches Python and the dependencies. Nothing is installed system wide, and the whole of it lives in a cache directory you can delete. A browser opens on the first family it finds.

What you unpack holds the launcher, your fonts folder, and a versions folder with the code in it. The launcher runs whichever version current names, so a later release is added beside this one and never written over it.

CrossGlyph looks for a newer release about once a day and says so when there is one. crossglyph update, or the button in the preview, installs it beside the version you are on and leaves your fonts and your settings alone. A local preview restarts on the new version and reloads the page; a command-line update waits for you to close CrossGlyph and open it again. crossglyph update --rollback goes back. Nothing is downloaded or installed until you ask, and one line in update.conf turns the looking off. See docs/updating.md.

Step 3 is second on purpose: there is nothing to set up before the first run. An empty workspace opens on Literata, which ships with the tool, so the page has type on it while you decide what to tune. Add a font of your own and it takes over.

To build every family in the workspace, with no page in between:

./crossglyph.sh build

To keep the preview running without a terminal window holding it open, there is start, status, restart and stop. start opens a browser once the page answers, restart comes back on the same address and picks up an update if one has been installed, and stop --port 8123 names a preview on another address instead of the one this install started. docs/preview.md has the rest.

Windows on ARM is the one platform without ready-made wheels: freetype-py publishes none, so uv tries to compile it and needs a build toolchain.

Docker

Docker can run the preview and command-line builds with only the fonts workspace mounted from the host. On Windows:

crossglyph-docker.cmd

On macOS or Linux:

./crossglyph-docker.sh

The launcher waits for a healthy preview, then prints its browser address, the mounted workspace and the commands for logs and shutdown. Add --local to build from the unpacked release or checkout instead of pulling CrossGlyph's published image. The image installs nothing on the host and publishes the preview on 127.0.0.1 by default. docs/docker.md covers the raw Compose commands, image tags, batch builds and remote hosting.

The workspace

The fonts folder sits beside the launcher, outside versions, so an update only ever adds to it: a file you edited is kept, with the new one written beside it as <name>.new. It holds four things:

fonts/
  NotoSans-Regular.ttf   your font files, at the root
  NotoSans-Bold.ttf
  conf/                  one <family>.conf per family, and all.conf
  fallbacks/             the bundled Noto faces, once fetched
  cpfonts/               what gets built

$CROSSGLYPH_FONTS names another workspace, and so does --fonts DIR. Builds land in cpfonts unless out in all.conf says otherwise.

A family needs no config at all. Drop the regular, bold, italic and bold italic files in, name them the way their foundry did, and they build on the next run. all.conf holds settings shared by every family. It is yours and starts absent; copy all.conf.example beside it to start from a commented list of every key. Write a <family>.conf when one family needs settings the others do not. See docs/fonts.md for every key, and for what the tuning controls actually do.

Getting the fonts onto the device

Copy a built family folder from cpfonts into /fonts on the SD card, or into /.fonts to keep it out of the file browser. The device scans both at boot, and the family then appears under Settings > Reader > Font.

The point sizes offered are the ones you built. A family built at 12, 14 and 16 offers three of them.

Fallback faces

A codepoint is one character as the computer stores it, and CrossPoint draws nothing at all for one that no font in the chain has. A family with no arrow in it leaves a gap where the arrow should be. The bundled Noto faces fill those gaps, covering Hebrew, Arabic, Thai, Bengali, Armenian, Georgian, Ethiopic, Cherokee, Tifinagh, Coptic, mathematics, symbols and emoji.

They are OFL licensed and unmodified, so they are downloaded on request and not shipped here:

./crossglyph.sh fetch-fallbacks

That is a few megabytes, and it puts OFL.txt beside them. The face for Chinese, Japanese and Korean is a much larger download on its own, and it comes only when something has asked for it: a config naming one of those scripts, or, in the preview, text on the page that cannot be drawn without it. That one face covers Chinese in both its written forms, Japanese and Korean, so there is no choice to make between them.

The preview offers the same download as a button, with a bar, since it takes a while. Bundled fallbacks are off by default, which keeps a first build self-contained and makes a narrow face a fraction of the size. After fetching them, turn on bundled fallback faces in the preview or set fallbacks = yes in a config to fill codepoints the family lacks.

What is here

src/crossglyph/	the converter, the workspace rules and the preview server
src/crossglyph/cpfont/	the .cpfont writer, forked from the tool behind the CrossPoint website
src/crossglyph/render/	the firmware's renderer, compiled to WebAssembly, and the Python that drives it
src/render/	the C++ and the build script that produce that module
src/crossglyph/starter/	Literata, the family an empty workspace opens on
docs/	fonts.md for building, preview.md for the renderer, docker.md for containers, updating.md for the update check

CrossGlyph is MIT licensed. See THIRD-PARTY-NOTICES.md for the code it carries, and CONTRIBUTING.md to work on it.