`sfnt.rs` read the metric tables and nothing else. It could say how wide a
glyph was and not what shape it had, so every renderer drew embedded text
with a substitute font at the correct advance — the failure mode that looks
most like success: the line breaks land right and the letterforms belong to
somebody else.
`outline.rs` returns one outline type for both formats. TrueType quadratics
are degree-elevated to cubics, which is exact, so no format detail leaks to
a consumer. Composite glyphs are placed by their offsets and scales, with a
depth bound because a font can reference itself. CFF Type 2 charstrings run
through an interpreter with biased local and global subroutines, hints,
hintmask byte counting, the leading width operand, and the FontMatrix as
declared rather than assumed to be 1/1000.
Separately, `ShowTextWithMetrics` carried one advance for a whole run —
enough to move the pen to the next run and nothing else. So `text.rs`
guessed: `seg.advance / char_count`. For "Wi" that puts the boundary
between the letters at 5 when it is at 9, and every caret, drag-selection
and search highlight in the application was wrong by that much for every
proportional font. `GlyphPlacement` now carries per-glyph pen offsets,
computed with the same expression as the run total so the two cannot drift.
The even-spacing fallback stays for fonts with no width table, which is
what `advance_is_measured` has always been for.
The fixture story is ADR 0029's, again. `cff_sample.otf` is a fontTools
conversion of DejaVu: no subroutines, no hints, no width operands. It
proved the interpreter draws the right shapes, and then four mutations of
that interpreter survived because nothing in the corpus reached the code
they broke — each of which produces a plausible wrong glyph from a font
that parses. `cff_subrs.cff` is hand-assembled for exactly those four, and
fontTools agrees with every expectation asserted against it. A fifth
mutation survived a composite test that counted contours; it is killed now
by one that measures where the components land.
Coordinates are asserted against fontTools ground truth, not against our
own output. Seven mutations, all killed. 1397 tests pass.
Deferred and recorded, not claimed: CID-keyed CFF, `seac` accents,
rendering outlines through the Makepad device.
ADR 0031.
