CrossGlyph

Tune a font for an Xteink reader running CrossPoint, and watch the page redraw as you move each control. A change lands in 10 to 300 ms, depending on your hardware and how much of the font is being built.

Most fonts need tuning to read well at two bits per pixel. Until now every guess cost a card swap or an emulator run, so almost nobody went past changing the point size.

• the firmware's own renderer, its C++ compiled to WebAssembly, so the page is what the device draws rather than an impression of it
• fourteen rasterizing controls: gamma, the three grey thresholds, weight, slant, hinting mode, grayscale hinting, mono rasterizing, stem darkening, line height, letter and word spacing, kerning strength, ligatures, proportional figures
• eight page controls, so the page you judge is set up like the device you are judging for: margin, alignment, line spacing, hyphenation and the language its patterns come from, paragraph spacing, anti-aliasing and night mode
• variable fonts build at the weight their designer named, or at any weight you pick: left alone, Merriweather would ship its Light as your Regular
• four sizes of a four-style family, 795 glyphs each with kerning, built in about a second, one process per size
• thirteen Noto faces on request, so a missing arrow or Greek letter is not a hole in the page
• Arabic comes out joined with any face, because the joining rules a modern one stores are run here and the joined shapes built in, which the device has no room to do for itself
• nothing installed system wide, since the launcher fetches uv, Python and the dependencies into a cache directory you can delete

CrossGlyph turns TTF and OTF files into .cpfont, which is what the device reads: glyph bitmaps at two bits per pixel, one file per point size, kerning and ligature tables baked in. The device has no rasterizer, so every size is 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, which is how a later release can be added beside this one rather than 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 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 four files in, name them the way their foundry did, and they build on the next run. all.conf holds settings shared by every family and ships commented out, so it sets nothing until you edit it. Write a <family>.conf when one family needs settings of its own. 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

CrossPoint draws nothing for a codepoint no font in the chain has, so a family that lacks an arrow leaves a gap where it should be. Thirteen Noto faces fill those holes, covering Hebrew, Arabic, Armenian, Georgian, Ethiopic, Cherokee, Tifinagh, Coptic, mathematics, symbols and emoji.

They are OFL licensed and unmodified, so they are downloaded rather than shipped here:

./crossglyph.sh fetch-fallbacks

That is 3.4 MB, and it puts OFL.txt beside them. A CJK face is another 15.7 MB and comes only when something has asked for it: a config naming a CJK script, or, in the preview, text on the page that cannot be drawn without one. One face answers all four languages, Korean included, 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 about twelve times smaller. 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.