Parse glyf and OS/2 tables for glyph outline extraction #24

Phase 2: Pure Rust Font Engine#

Parse the remaining font tables needed for glyph rendering:

glyf table (Glyph Data)#

Extract TrueType glyph outlines from the glyf table:

• Simple glyphs: Parse glyph header (numberOfContours, xMin, yMin, xMax, yMax), endPtsOfContours array, instruction bytes, flags array, and x/y coordinate arrays (with delta decoding)
• Compound/composite glyphs: Parse component records with glyph indices, transformation matrices (scale, rotation, translation), and flags (ARG_1_AND_2_ARE_WORDS, WE_HAVE_A_SCALE, etc.)
• Handle flag bits: ON_CURVE_POINT, X_SHORT_VECTOR, Y_SHORT_VECTOR, REPEAT_FLAG, X_IS_SAME_OR_POSITIVE, Y_IS_SAME_OR_POSITIVE
• Use the already-parsed loca table to find glyph byte ranges within glyf

OS/2 table#

Parse the OS/2 table for font-wide metrics:

• sTypoAscender, sTypoDescender, sTypoLineGap
• usWeightClass, usWidthClass
• fsType (embedding restrictions)
• sxHeight, sCapHeight (if version >= 2)
• yStrikeoutSize, yStrikeoutPosition
• ySuperscriptYOffset, ySubscriptYOffset

Data structures#

• GlyphOutline with contours as Vec<Contour>
• Contour as Vec<Point> with on-curve/off-curve flags
• Point { x: i16, y: i16, on_curve: bool }
• Public API: Font::glyph_outline(glyph_id) -> Option<GlyphOutline>

Acceptance criteria#

• Simple glyph outlines are correctly extracted (test with known glyphs)
• Compound glyphs are flattened to simple outlines
• OS/2 table metrics are parsed and accessible
• All existing tests continue to pass
• cargo clippy --workspace -- -D warnings passes
• cargo fmt --all --check passes