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Font backend migration
The font stack uses released Skrifa 0.48.0, read-fonts 0.45.0 and HarfRust 0.14.0. Raw SVG text and rasterization use usvg/resvg 0.48.1. Font parsing, shaping and rendering remain in WASM with caller-injected fonts.
API and failure changes
The TypeScript render, registry and shaping signatures are unchanged. WASM schema 35 must be paired with the matching JavaScript package; older schema 34 artifacts are rejected. Native boundtext callers must replace the old backend modules/types/features with backend_skrifa::SkrifaBackend / skrifa-backend and backend_harfrust::HarfRustShaper / harfrust-backend. The custom backend traits remain available. The workspace requires Rust 1.88.0 or later.
FontBackend::create_face_with_admission can reuse proof for an exact immutable allocation; custom implementations keep their shared-face factory by default. Missing or mismatched proof still requires admission. Native outline::extract_glyph_paths now accepts a &dyn FontFace at the desired variation location. Construct or obtain that face first, then reuse it for the whole extraction instead of passing raw font bytes to the outline operation.
FontRegistry::rasterize_font_data now returns Result<RasterizeFontData, BoundtextError>. The snapshot has aliases, fonts and aligned optional admissions fields. Snapshot allocation failures propagate before rasterization. The built-in renderer checks each proof against the exact immutable font allocation; missing or mismatched proofs take full admission. Animation sessions retain proofs only with their font snapshot and release them on finish, abort or failure. Standalone native raster functions still admit raw bytes. Custom Renderer implementations retain their existing methods through the provided proof-aware defaults.
Native metrics and control bounds now use finite f64 values in font units. Shape and outline operations return Result; legitimate absent metrics and empty glyphs use Option inside the result. Drawing and shaping failures do not produce successful partial output. A present but malformed table used for metrics or shaping now fails registration or the operation; optional table absence remains valid. Unknown unused tables are ignored.
| Diagnostic | Meaning |
|---|---|
FONT_PARSE_FAILED | Font container, metric table or shaping admission failed. |
FONT_OUTLINE_FAILED | Glyph ID, positioned-glyph input or outline drawing failed. |
TEXT_SHAPING_FAILED | Input, buffer preparation or the shaping operation failed. |
TEXT_SHAPING_LIMIT_EXCEEDED | The shaper reported buffer failure during processing, including possible allocation or operation limits. |
TEXT_SHAPING_INVALID_OUTPUT | Returned glyph arrays, glyph IDs or UTF-8 clusters violate the font contract. |
TEXT_FONT_UNAVAILABLE | No requested alias resolves to a registered font, including an empty fallback chain. |
FONT_DUPLICATE | Native font registration reported an existing entry. |
Fixed messages and typed context
The WASM/TypeScript transport preserves these exact message, stage and reason combinations. Different messages under the same code describe different failures; callers must not replace one with another.
| Diagnostic | Fixed message | Stage | context.reason |
|---|---|---|---|
FONT_PARSE_FAILED | Font parsing or admission failed. | font | invalidData, missingTable, invalidTable, noOutlines, invalidUnitsPerEm, invalidGlyphCount, nonFiniteMetric, invalidVariationAxis, allocationFailed |
FONT_OUTLINE_FAILED | Font outline extraction failed. | font | invalidGlyphId, nonFiniteMetric, allocationFailed, drawingFailed |
FONT_OUTLINE_FAILED | Baseline glyph rotation must be finite. | font | invalidBaselineRotation |
FONT_OUTLINE_FAILED | Glyph inline scale must be positive and finite. | font | invalidInlineScale |
TEXT_SHAPING_FAILED | Text shaping failed. | text | nonFiniteVariation, nonFiniteMetric, allocationFailed, bufferPreparationFailed, inputTooLong, alreadyShaped, directionUnset, planMismatch, shapingFailed |
TEXT_SHAPING_LIMIT_EXCEEDED | The shaping buffer failed during processing. | text | bufferFailedDuringShaping |
TEXT_SHAPING_INVALID_OUTPUT | The shaper returned invalid glyph data. | text | invalidGlyphId, invalidCluster, parallelArrayLengthMismatch |
TEXT_FONT_UNAVAILABLE | No requested font is available. | font | unregisteredFont |
TEXT_FONT_UNAVAILABLE | No requested font is available for text layout. | text | Layout preparation uses run/alias context without a reason field. |
FONT_DUPLICATE | The font is already registered. | font | duplicateRegistration |
The native font-classification forms include context.operation and the typed context.reason. Parse errors also include the zero-based faceIndex and, when applicable, a four-character OpenType table tag; an absent tag is omitted rather than null. Ordinary outline failures include the requested glyphId; the two positioned-glyph argument failures do not. Invalid shaped output includes glyphIndex, the zero-based output-record index rather than a glyph ID or UTF-8 cluster. The font-stage unavailable form includes the requested weight. The text-stage layout-preparation form instead carries the bounded effective-run and requested-alias context documented in the text layout diagnostic guide.
Rendering preserves node identity when available. Dependency-internal infallible allocations and process-wide memory exhaustion are not guaranteed to be recoverable. Raw SVG text uses usvg’s own shaping path and error visibility.
Geometry and reproducibility
Horizontal line metrics retain explicit OS/2/hhea/typographic/Win selection; they do not switch to the new libraries’ default line-height policy. Normal line height keeps its 1.2em floor and explicit line height keeps half-leading and baseline placement. Registration metrics remain at the default variation location; per-call variation settings cannot change shared registration state. Vertical VORG/vmtx origins, typographic fallback and rotated glyph placement remain the responsibility of the text engine’s final positioning.
Unsigned Win metrics no longer wrap through i16. Outlines use official, unhinted floating point drawing, and control bounds include emitted endpoints and curve control points. They are not tight curve bounds. Fractional variation metrics are retained, and normalized axis-coordinate quantization can differ from previous versions. Fonts with 65,535 glyphs, including a nonempty last glyph, no longer require a vendored parser.
Raw SVG text follows usvg's optical sizing behavior: when a variable font has an opsz axis, font-optical-sizing: auto selects an optical size from the font size. This can change outlines from older versions. Use font-optical-sizing: none or an explicit font-variation-settings: "opsz" 14 when the SVG needs a fixed optical size. This does not implicitly add an opsz setting to the declarative Text API.
SVG text, geometry, decoded RGBA pixels and encoded PNG/WebP/GIF bytes are separate comparison surfaces. Font and raster library upgrades can change them across versions. The byte reproducibility guarantee applies to repeated runs within one matched version and the documented input domain; compare outputs before upgrading pinned versions.
PNG encoding explicitly selects fast compression and the Sub filter to retain the established encoding-speed policy across dependency upgrades. This remains a lossless RGBA path; no new PNG quality option is required.
Raster backend feature
The resvg-backend and explicit default Cargo feature names are removed in 0.9.0. The boundsvg crate always includes its rasterization dependencies. Remove these selectors from dependency manifests and --features arguments, including forwarded package selectors. Normal dependency declarations and default-features = false remain valid and do not disable rasterization. The Renderer injection API remains available; custom renderers do not exclude the standard raster dependencies from the build.