# Feature Status
This document keeps the implementation-oriented notes that were previously in `README.md`.
The README now focuses on the public API and runnable examples.
## Layout support
`layout` is partially implemented.
### GSUB
- Parsed: `ScriptList`, `FeatureList`, `LookupList`
- Implemented: `lookup_vertical()` for single-substitution vertical forms
- Partial: `lookup_ccmp()` exists but does not expand all results yet
- Implemented: `lookup_locale()` and `lookup_liga()`
- Text APIs apply variation selectors and basic `locl` / `liga` / `dlig` / `ccmp`
- Direction-aware APIs support vertical flow and RTL layout
- Arabic shaping currently covers `isol` / `init` / `medi` / `fina`
- Arabic shaping also applies `rlig`, `rclt`, `calt`, and `clig` when present
- Locale-aware lookup collection prefers matching scripts such as `arab`, `hebr`, and `syrc`
- Language-system selection also uses full locale subtags such as `ur-Arab-PK`
- Japanese variant forms can be requested through `FontOptions::font_variant`
- Context/chaining support is partially wired through the feature-sequence engine
- Not implemented: `lookup_width()`, `lookup_number()`
### Lookup parsing
- Type 1 Single Substitution: parsed and expandable
- Type 2 Multiple Substitution: parsed and expandable
- Type 3 Alternate Substitution: parsed and expandable
- Type 4 Ligature Substitution: parsed and expandable
- Type 5 Context Substitution:
- Format 1 parsed, partially applicable
- Format 2 parsed, partially applicable
- Format 3 parsed, applicable
- Type 6 Chaining Context Substitution:
- Format 1 parsed, partially applicable
- Format 2 parsed, partially applicable
- Format 3 parsed, applicable
- Type 7 Extension Substitution: parsed, not fully applied
- Type 8 Reverse Chaining Contextual Single Substitution: parsed, not applied
### GDEF
- Parsed: glyph class definitions, attach list, ligature caret list, mark attach class definition, mark glyph sets definition
- Current state: partially integrated
- Pair positioning now skips GDEF mark glyphs when searching previous/next spacing glyphs for kerning
- `GPOS mark-to-base` (Type 4 Format 1) is now parsed and used during shaping when a `mark` feature lookup is available
- `GPOS mark-to-mark` (Type 6 Format 1) is now parsed and used during shaping when an `mkmk` feature lookup is available
- When neither `GPOS mark-to-base` nor `mark-to-mark` anchors are available, shaping still falls back to the existing GDEF-based mark attachment heuristic
- Attach / caret / mark-set data is still not fully integrated into higher-level layout
## Notes
- `FontFamily` currently supports cached-face selection and per-glyph fallback across loaded faces
- Family fallback chains and Last Resort handling are still not implemented
- Variable-font metadata and axis-driven metrics are available through `fvar` / `avar` / `HVAR` / `VVAR` / `MVAR`
- Public API axis entry points are `FontFace::variation_axes()` and `FontEngine::with_variation()`
- `gvar` outline deltas now cover both simple glyphs and composite glyphs, including recursive component variation for Source Serif variable-font fixtures
- `gvar` phantom-point deltas now feed horizontal and vertical glyph metrics in both layout getters and shaping output
- Phantom-point behavior is covered by synthetic unit tests and Source Serif real-font regressions
- Parser hardening is in progress: malformed optional GSUB/GPOS feature-variation data is now skipped instead of panicking
- Unsupported contextual GSUB subtables now fall back to `LookupResult::None` instead of panicking during shaping
- `hmtx` / `vmtx` now tolerate zero-metric edge cases without panicking, returning zero advances as a fallback
- `OTFHeader`, `TTCHeader`, `get_font_type()`, and `COLR::new()` now return errors instead of panicking on truncated input
- `COLR::get_layer_record()` now stops at available layers instead of trusting malformed layer ranges
- `fontreader.rs` now removes more public-path `unwrap()` calls in name lookup, metrics/layout getters, and mandatory-table loading
- CFF2 outlines now load through the shared `cff.rs` path, including `vsindex` / `blend` evaluation and real-fixture SVG smoke coverage
- CFF2 variation support now covers both outline charstrings and Private DICT `vsindex` / `blend` parsing
- The current local corpus does not contain a confirmed real CFF2 font; coverage is therefore synthetic/unit-test heavy until a true CFF2 fixture is added
- With `svg-fonts`, OpenType `SVG ` glyphs are pathified first, and simple shapes are emitted as `GlyphLayer::Path`
- Payloads that cannot be pathified, and payloads that still contain unsupported constructs such as `pattern`, `mask`, or `filter`, are kept as `GlyphLayer::Svg` fallback layers
- The current supported SVG subset covers `path`, `rect`, `circle`, `ellipse`, `line`, `polyline`, `polygon`, `defs` / `use`, `fill` / `fill-rule` / `stroke` / `stroke-width`, `clipPath` / `clip-path`, simple `mask`, `translate` / `scale` / `rotate` / `skewX` / `skewY` / `matrix`, minimal `linearGradient` / `radialGradient` / `stop`, and preserved `gradientUnits` / `gradientTransform`
- Patterns, `mask`, `filter`, and richer stroke styles are still unsupported
- The `paintcore` bridge now preserves clip/gradient-capable layer data from the public 0.0.12 `fontcore` line
- WOFF2 still requires the complete byte stream before decoding
- CFF2 planning notes live in `cff2-investigation.md`