Fix #190 — font lookup: registered, system and bundled faces

[sbeitzel]

Fix #190

What changed

• FontRequest (public): a family, weight (regular/bold) and style (upright/italic, with oblique counted as italic).

  • init(postScriptName:) parses Times-Roman, Times-BoldItalic, Helvetica-Oblique, Courier-Bold and similar names, and keeps the original name for an exact match.
  • The base 14 and serif/sans-serif/monospace come with stand-in lists, following abcm2ps (serif = Times, sans-serif = Helvetica): the macOS/Windows equivalents, then Liberation, Nimbus (URW) and DejaVu.

• FontLibrary (public, immutable, Sendable): fonts the host supplies as Data, CFF or TrueType, single fonts or collections (OpenTypeFont: read TrueType (glyf) outlines and font collections (.ttc) #189), parsed once.

  • Set it on SVGRenderConfig.fontLibrary.
  • It is part of the config rather than a process-wide registry, so the same config always gives the same output, and tests don't affect one another.

• SVGRenderConfig.systemFonts, default false, uses installed fonts on Apple platforms. On Linux there is no system lookup; a host supplies fonts through FontLibrary instead.

• FontProvider resolves a request:

  • It searches the host's fonts, then system fonts, then the bundled ones. For each family (the requested one first, then its stand-ins), an exact match from any source beats a near match.
  • A face whose fsType forbids embedding is skipped when outlining.
  • Results are cached per render.
  • The emitter's own Bravura and Libertinus Serif requests go straight to the bundled fonts, so existing output is unchanged. The snapshot tests pass.

• FontResolution (public) records the face used, its origin and any faces refused. diagnostics(at:) produces two new codes:

  • .fontSubstituted: an info note when a stand-in answered, otherwise a warning;
  • .fontNotEmbeddable: a warning.

  Support the §11.4.2 font directives (%%titlefont, %%vocalfont, %%wordsfont, …) #186 will report these against the directive that named the font.

• FaceKey is now an open-ended key. The bundled fonts keep their <defs> ids, and other fonts get f-<PostScript name>.

• TextOutliner.outline(_:font:fontSize:fill:library:systemFonts:) draws text in a named font. OutlinedText.resolution reports which face was used.

• OpenTypeFont now also reads the family name (name ID 16, else 1), usWeightClass and the italic flag. Where a font has no OS/2 table (macOS's own Courier.ttc), weight and italic come from head.macStyle.

A deliberate departure from the issue

The issue suggested converting CoreText glyph paths (CTFontCreatePathForGlyph → CGPath → GlyphPath). Instead, CoreText is used only to find the font file and face name, and the file is read by our own parser from #189. As a result, every face, wherever it came from, goes through the same measuring, outlining and fsType checks, and a system font draws exactly as the same file supplied by a host would. A system font in a format we can't read is skipped.

Lookups pass the family or PostScript name as a mandatory attribute. Otherwise CoreText answers any query, including one for a family that isn't installed, with some fallback face (usually Helvetica).

Tests (FontProviderTests, 14)

• PostScript-name parsing and stand-in lists.
• A host-supplied fixture font (from OpenTypeFont: read TrueType (glyf) outlines and font collections (.ttc) #189) is drawn when named, by PostScript name or by family: the fixture's "A", not Libertinus's. Its diagnostics are empty.
• A request for a weight the family lacks is answered by the nearest face, flagged as a substitute.
• A restricted (fsType 0x0002) face is refused, producing fontNotEmbeddable and fontSubstituted.
• An unreadable font in the library is reported by its position.
• With nothing supplied and system lookup off, the bundled fonts answer everything, with a warning.
• The bundled fonts keep their keys.
• SVGBuilder writes f-CeolKitTest-Regular-g… glyph definitions for a host-supplied font.
• macOS:
  • with system lookup on, Courier-Bold resolves through CoreText to the system's Courier-Bold and is outlined (0.6 em monospaced advances);
  • serif italic → Times-Italic, reported as an info note;
  • system lookup is off by default;
  • a family that isn't installed is not answered by CoreText's fallback.

swift test: all tests pass on macOS. Linux: built and tested in the swift:6.3 container as CI does, and all 1,420 tests pass (the CoreText tests compile out).

Not yet wired

Nothing in a document names a font yet. #186 will map the font directives onto FontRequest, report FontResolution diagnostics at the directive's source, and route layout measurements through the provider. #191 builds on FontResolution and FontLibrary.

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