SharpAstro.Fonts.Shaping 1.9.751

SharpAstro.Fonts

A pure-managed, MIT-licensed C# library for loading and rendering OpenType / TrueType fonts.

Status

All phases complete. TrueType hinting, CFF outlines, COLR v0/v1 color glyphs, bitmap emoji, variable fonts, PostScript Type 1, WOFF/WOFF2, and CJK variation selectors. 155 tests passing across outline, rasterizer, color, hinting, variation, and CJK baseline suites.

Goals

• 100% managed C#, AOT-compatible, no native dependencies.
• Cross-platform — targets net10.0, runs on x64 (Windows, Linux, macOS) and ARM64 (Windows on ARM, Apple Silicon, Linux ARM64). SIMD hot paths use Vector<T> to auto-scale across SSE2 / AVX2 / AVX-512 / AdvSIMD.
• Thread-safe by construction (immutable font records, per-call rasterizer state, lock-free hinting snapshot cache).
• MIT-licensed end to end. No code is copied from FreeType, SixLabors.Fonts, HarfBuzz, or other non-MIT sources.
• Feature parity with the FreeType subset needed for PDF rendering and UI text.

Supported formats

Container formats

AutoCAD SHX

The format DWG text styles use, and the reason SHX text in a plotted PDF arrives as bare path geometry with no font object and no /ToUnicode behind it — which makes it invisible to every text extractor. ShxFont is deliberately separate from OpenTypeFont: it shares no tables, no cmap and no SFNT structure.

The one thing that behaves unlike every other format here: SHX is stroked, not filled. A glyph is a pen path whose width comes from the graphics state (the w operator in PDF), never from the font, and there is no filled counter — the bowl of an O is a stroked circle, not two contours. So TryGetGlyph emits an open path and never calls Close(). Consumers wanting geometry (text extraction, shape matching, hit-testing) take it directly; consumers wanting something fillable go through TryGetStrokedOutline or RenderGlyph with a width of their choosing.

Shape libraries (AutoCAD-86 shapes — simplex.shx, ACAD.SHX, P&ID and survey symbol sets) are rejected with NotSupportedException. They are not text fonts: their records are addressed by shape number from a DWG rather than by character code, so there is no character mapping to read.

Validated against 4,428 stock and third-party .shx files: 470,156 glyphs decode without an exception, 99.0% of them producing geometry. That corpus cannot be bundled (Autodesk's faces are their IP; this repo is MIT end to end), so CI runs against two fixtures authored from scratch by tools/make_shx_fixtures.py. Point SHX_TEST_FONT_DIR at a local directory of .shx files to run the breadth suite in ShxRealFaceTests.

OpenType tables

Core

Character mapping (cmap)

Not implemented: formats 2 (high-byte CJK legacy), 8 (mixed 16/32), 13 (last-resort).

Outlines

Not implemented: CFF2 (blend operator, uint32 INDEX counts).

TrueType hinting

Full v40 grayscale interpreter: ~150 opcodes including DELTAP1/2/3, DELTAC1/2/3, ISECT, engine compensation, IUP, SHP/SHC/SHZ, all round modes, function defs, projection/freedom/dual vector setters. Per-(face, ppem) HintingSnapshot cache with thread-safe per-call clone.

Color

Not implemented: sbix (Apple bitmap strikes), non-PNG CBDT image formats.

Variable fonts

Not implemented: avar v2 (non-linear ItemVariationStore remapping).

Kerning / positioning

Not implemented: Apple kern v1, kern format 2, GPOS lookup types 1/3–9.

Shared variation infrastructure

Rasterizer

PostScript Type 1

Not implemented: .pfa ASCII format, standalone CID Type 0 (CID-keyed CFF is supported via the CFF1 parser).

License

MIT — see LICENSE.

Specifications used as reference

All public, freely-implementable specs:

• OpenType (Microsoft)
• CFF / Type 2 charstrings (Adobe)
• TrueType instruction set (Microsoft / Apple)
• WOFF / WOFF2 (W3C)
• COLR (Microsoft / Google)
• Unicode UAX (Unicode Consortium)

Layout

src/SharpAstro.Fonts/                   pure library
tests/SharpAstro.Fonts.Tests/           xUnit v3 tests + font fixtures
benchmarks/SharpAstro.Fonts.Benchmarks/ BenchmarkDotNet perf suite

Development history

Developed in 12 phases, each validated against golden output:

1. SFNT skeleton + cmap
2. TrueType outlines (glyf/loca, composite glyphs)
3. Smooth rasterizer (analytic coverage)
4. CFF1 (Type 2 charstring interpreter, CID-keyed fonts)
5. COLR v0/v1 + CPAL (paint tree, gradients, composite modes)
6. CBDT bitmap glyphs (PNG emoji)
7. Variable fonts (fvar/avar/gvar/cvar/HVAR/VVAR/MVAR)
8. TrueType bytecode hinting (v40 grayscale, ~150 opcodes)
9. PostScript Type 1 (.pfb)
10. SDF rasterizer, kern/GPOS kerning, stroker, vertical metrics
11. WOFF / WOFF2
12. DIR.Lib integration (replaced FreeType native bindings)