oxideav-ttf

Pure-Rust TrueType font parser for the oxideav framework. Implements the sfnt container, the core OpenType tables, and just enough of GSUB / GPOS to do Latin/Cyrillic/Greek/CJK shaping with ligatures and kerning.

Round-1 scope (this release)

• sfnt + table directory walker.
• head, hhea, maxp, cmap (base formats 0, 4, 6, 12 + format 14 Unicode Variation Sequences as a sidecar), name, OS/2, hmtx, loca, glyf (simple + composite), post.
• Legacy kern table (format 0).
• GSUB LookupType 4 (ligature substitution).
• GPOS LookupType 2 (pair-adjustment / kerning).
• GDEF (glyph class definitions, used to skip mark glyphs).

The companion oxideav-scribe crate consumes the outlines + shaping output to rasterise text to RGBA bitmaps for subtitles and the scene compositor.

Public API

use oxideav_ttf::Font;

let bytes = std::fs::read("DejaVuSansMono.ttf")?;
let font  = Font::from_bytes(&bytes)?;

// Metadata.
let _ = font.family_name();         // Some("DejaVu Sans Mono")
let _ = font.units_per_em();        // 2048
let _ = font.glyph_count();
let _ = font.ascent();
let _ = font.descent();
let _ = font.line_gap();

// Glyph lookup.
let gid_a = font.glyph_index('A').unwrap();
let _ = font.glyph_advance(gid_a);  // i16 advance width in font units
let _ = font.glyph_lsb(gid_a);
let _ = font.glyph_bounding_box(gid_a);
let _ = font.glyph_outline(gid_a)?; // contours of i16 points

// Shaping helpers.
let gid_f = font.glyph_index('f').unwrap();
let gid_i = font.glyph_index('i').unwrap();
if let Some((replacement_gid, consumed)) = font.lookup_ligature(&[gid_f, gid_i]) {
    // `fi` ligature substitutes 2 input glyphs with `replacement_gid`.
    let _ = (replacement_gid, consumed);
}

let gid_v = font.glyph_index('V').unwrap();
let _ = font.lookup_kerning(gid_a, gid_v); // negative i16 in font units

// Unicode Variation Sequences (cmap format 14). Used by emoji
// presentation selectors and registered IVS for CJK.
let _ = font.lookup_variation('\u{1F600}', '\u{FE0F}'); // grinning face + VS-16

// Colour glyphs — three families covered:
//
//   COLR/CPAL: vector layer stack (Microsoft Segoe UI Emoji, Twemoji-Mozilla, …)
//   CBDT/CBLC: PNG-payload bitmap strikes (Noto Color Emoji and friends)
//   sbix:      Apple-style PNG/JPEG bitmap strikes (Apple Color Emoji)
//
if font.has_color_layers() {
    for layer in font.color_layers(gid_a) {
        let rgba = font.cpal_color(0, layer.palette_index); // Option<[u8;4]>
        let _ = (layer.layer_glyph_id, rgba);
    }
}
if font.has_color_bitmaps() {
    let _ = font.glyph_color_bitmap(gid_a, /* target_ppem */ 64);
}
if font.has_sbix() {
    let _ = font.sbix_glyph(gid_a, /* target_ppem */ 64);
}

// TTC (TrueType Collection) — pick one subfont from a `.ttc` file.
let _ = oxideav_ttf::is_collection(&bytes);
let _ = Font::from_collection_bytes(&bytes, /* index */ 0);

// Variable fonts (fvar / avar / gvar). Pick a coord vector in
// user-space units (e.g. wght 100..900); glyph_outline() then
// returns the gvar-deltad outline.
let mut vfont = Font::from_bytes(&bytes)?;
if vfont.is_variable() {
    for axis in vfont.variation_axes() {
        // axis.tag, axis.min, axis.default, axis.max, axis.name_id
    }
    for inst in vfont.named_instances() {
        // inst.subfamily_name_id + inst.coords
    }
    let mut coords = vfont.variation_coords().to_vec();
    if let Some(i) = vfont.variation_axes().iter().position(|a| &a.tag == b"wght") {
        coords[i] = 700.0;
    }
    vfont.set_variation_coords(&coords);
    let bold = vfont.glyph_outline(vfont.glyph_index('A').unwrap())?;
    let _ = bold;
}

Out of scope (round 2+)

• CFF / Type 2 charstrings — moves to a sibling oxideav-otf crate.
• Bidi, Arabic shaping, Indic conjuncts, complex contextual GSUB/GPOS.
• TrueType bytecode hinting (modern AA at ≥ 16 px does not need it).
• cmap formats 2, 8, 10, 13.
• GSUB lookup types 1/2/3/5/6/7/8 and GPOS lookup types 1/3..9.
• COLR v1 paint graph (gradients, transforms, composites) — only the v0 flat layer stack is supported.
• sbix 'dupe' chasing (the indirection sentinel is surfaced as-is; consumers chase it with their own cycle detection).
• avar v2 delta-set index map (variable-axis remap).
• HVAR / VVAR / MVAR (per-glyph horizontal-metrics / vertical-metrics / per-table metric variations).
• gvar delta propagation into composite-glyph component offsets and the four phantom points.

Test fixtures

• tests/fixtures/DejaVuSansMono.ttf is the upstream DejaVu Sans Mono 2.37 under the Bitstream Vera license (see tests/fixtures/DEJAVU-LICENSE).
• tests/fixtures/InterVariable.ttf is Inter 4.0 (variable font, wght + opsz axes) under the SIL Open Font License 1.1 (see tests/fixtures/INTER-OFL-LICENSE.txt).

License

MIT — see LICENSE.