Milky2018/moon_cosmic

MoonBit port of Rust cosmic-text (text shaping, layout, and editor primitives), built on top of Milky2018/moon_swash.

The project keeps behavior aligned with upstream cosmic-text through automated tests where feasible.

Features

• Font system (in-memory): load TTF/OTF/TTC bytes; resolve fonts by family + weight; per-codepoint fallback.
• Shaping: Shaping::Advanced uses moon_swash/shape to produce clustered glyphs and advances; tabs snap to stops.
• Wrapping & layout: Wrap::{None,Glyph,Word,WordOrGlyph}, Align::{Left,Right,Center,Justified,End}, hinting.
• BiDi: paragraph iteration + embedding levels and visual reordering of glyph runs.
• Raster cache: CacheKey + SwashCache backed by moon_swash/scale (variable wght axis support; fake-italic transform).
• Editor primitives: Buffer, Editor, cursor/selection, hit-testing, and motion actions.

Install

Add dependency:

moon add Milky2018/moon_cosmic

Quick Start (Layout)

import Milky2018/moon_cosmic

fn main {
  // Provide font bytes from your host app (file I/O is app-specific).
  let font_bytes : Bytes = /* ... */

  let font_system = FontSystem::new().load_font_data(font_bytes)
  let metrics = Metrics::new(14.0F, 20.0F)

  let attrs = Attrs::new().family(Family::Name("Inter"))
  let attrs_list = AttrsList::new(attrs)

  let buffer = Buffer::new(metrics)
    .set_wrap(Wrap::WordOrGlyph)
    .set_text("Hello world", attrs_list, Shaping::Advanced)
    .set_size(Some(200.0F), None)
    .layout_all_with_font_system(font_system)

  for run in buffer.layout_runs() {
    // `run.glyphs`: Array[LayoutGlyph]
    // `run.line_w`: line width in pixels
    ignore(run)
  }
}

Quick Start (Draw)

Buffer::draw renders via a callback (pixel-oriented for compatibility with the legacy renderer pattern).

import Milky2018/moon_cosmic

fn draw_demo(font_bytes : Bytes) -> Unit {
  let font_system = FontSystem::new().load_font_data(font_bytes)
  let cache = SwashCache::new()

  let buffer = Buffer::new(Metrics::new(14.0F, 20.0F))
    .set_text("Hi!", AttrsList::new(Attrs::new()), Shaping::Advanced)
    .set_size(Some(200.0F), None)

  let (_buffer, _cache) = buffer.draw(
    font_system,
    cache,
    Color::rgb(0, 0, 0),
    fn(_x, _y, _w, _h, _color) { () },
  )
}

Integration Notes

Subpixel Cache Keys (Atlas Caching)

Downstream atlas caches should key by PhysicalGlyph.cache_key (includes x_bin/y_bin), not only (glyph_id, x, y).

Font Collections (TTC / Multi-face)

FontSystem::load_font_data may load multiple faces from one file/collection. Each face gets its own font_id. Use FontSystem::get_font(font_id) / FontSystem::get_font_entry(font_id) to rasterize the correct face for a given LayoutGlyph.

Dev Workflow

Common commands:

moon check        # Lint/type-check
moon test         # Run tests
moon fmt          # Format
moon info         # Update .mbti
moon info && moon fmt

Test Font Blob

Some tests require real font metrics. This repo embeds Inter-Regular.ttf into src/test_fonts_test.mbt (base64).

To regenerate it (if test font data changes):

python3 scripts/gen_test_font_mbt.py
moon fmt
moon test

License

Apache-2.0. Upstream cosmic-text is dual-licensed MIT OR Apache-2.0.