Module mbox

Expand description

The layout node model — the engine shape the G0-3 ratification froze — and the public output types of the frozen API sketch.

Two layers:

The public output: Layout — flat, positioned PlacedGlyph/PlacedRule/PlacedPath lists in em units, y-up, baseline at 0 — is what consumers (franken_manim’s fmn-tex; fmd’s HTML/PDF renderers) read. Every glyph names its face (multi-face layout is structural: ∑ ∫ ∏ resolve through the math-symbol fallback face) and carries its source span (§11.3 span provenance).
The internal node model: [MBox]/[MNode] — boxes, glue, and kerns, built bottom-up by the Appendix-G constructions and flattened into a Layout at the end. Fixed here (this bead) so the placement mathematics and the extension beads build on one shape.

typeset itself lands with the placement bead (fm-hk9); this module fixes the shapes both sides compile against.

Structs§

FaceId: Identifies one of the faces handed to the engine (an index into the engine’s face list, in construction order). Multi-face layout is structural: face selection is data on every glyph, never a rendering afterthought.
Layout: The final layout of a formula: flat positioned primitives plus overall metrics. Everything is in ems of the base size, y-up, baseline at 0; width spans the whole formula, height rises above the baseline, depth extends below it (a positive number).
PathContour: One closed contour of a drawn path: a start point plus segments; the contour closes back to the start implicitly.
PlacedGlyph: A positioned glyph in the final layout. Units are ems of the base (text-style) size; y is the baseline-relative vertical position, positive up; size is the glyph’s own size factor (1.0 / 0.7 / 0.5 per style).
PlacedPath: A positioned drawn-path construction (parametric delimiters past the glyph-scaling threshold, the drawn radical, braces): quadratic contours in ems, y-up, the same path model franken_manim’s geometry kernel and fmd-font outlines share.
PlacedRule: A positioned rectangular rule (fraction bars, \overlines, radical overbars). x/y name the rule’s left-bottom corner in ems, y-up.