Module font_face

Glyph source: outlines extracted on first use, never up front.

A face keeps its file bytes and rebuilds the ttf_parser::Face on demand — parsing one is table-offset arithmetic, so the cost lands in the noise next to the outline work it guards. Each glyph’s outline is turned into a [tiny_skia::Path] the first time it is asked for and cached for the process lifetime; rasterising then fills that path into an 8-bit coverage [Mask].

The eager alternative — building every glyph in the cmap when the face is constructed — costs 330 MB and 1.7 s of CPU for a 44 810 glyph CJK collection, to draw the hundred or so glyphs a screen actually shows. A single arrow or bullet resolving through the fallback chain was enough to pay it in full.

Metrics, OutlineBounds and LineMetrics keep the layout conventions the renderers and widgets already lay text out with: sizes scale by px / units_per_em, bounds is the outline box in subpixels, ymin grows upwards from the baseline, and the bitmap runs row-major from its top-left corner.

Structs

• ColorGlyph
  A glyph drawn as a colour image rather than an outline. The box is in ems, from the pen on the baseline, y up: scale it by the text size in pixels.
• FontFace
  A font face that materialises glyphs on demand.
• LineMetrics
  Vertical metrics of a face at a given size.
• Metrics
  Placement and size of one rasterised glyph.
• OutlineBounds
  Bounding box of a glyph’s outline, in subpixels, ymin upwards from the baseline.