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Add MVAR support - #420
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lehni wants to merge 4 commits into
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Add MVAR support#420lehni wants to merge 4 commits into
lehni wants to merge 4 commits into
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lehni
commented
Oct 26, 2026
lehni
commented
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- Builds on Follow HarfBuzz for the font metrics, and fix vhea and empty glyphs #419, whose metrics it varies; only the last two commits are new here
- Read the MVAR table and vary the ascent, descent, line gap, cap height, x-height and underline metrics of a variation by their deltas, whichever table each metric comes from, as HarfBuzz does
- Pierre-Henri Toussaint wrote the MVAR support; the last commit is my follow-up
- Tests use HarfBuzz's values for Playwrite and Recursive, two OFL fonts from HarfBuzz's test suite, and Mada
- Fix the vhea table structure - Give empty glyphs zero coordinates instead of infinite ones - Read the maxp, post and vhea versions as 16.16 version numbers - Respect the useTypoMetrics flag for the font's ascent, descent and line gap, and add lineHeight - Fix an undefined control box in the glyph metrics
- Use the typo metrics only when the font sets useTypoMetrics and the hhea metrics otherwise, with a positive ascent and a negative descent, as HarfBuzz does, instead of FreeType's fallbacks - Drop lineHeight, which HarfBuzz doesn't have and clients can derive - Expect HarfBuzz's vertical advance for Open Sans's space, which has no vmtx and doesn't set useTypoMetrics - Add tests for the typo metrics, the vertical advance without vmtx, the vhea and maxp versions, and empty CFF glyph boxes, with HarfBuzz's values
- Read the MVAR table and compute its adjustments for a variation of the font - Apply them to the typo ascent, descent and line gap, the cap height and the x-height
- Vary each metric by its MVAR delta whichever table it comes from, so fonts without useTypoMetrics also vary their ascent, descent and line gap, as HarfBuzz does - Vary the underline position and thickness too - Fall back to the ascent for the cap height without calling the metrics again, which recursed in fonts without OS/2 - Add tests with Playwrite, Recursive and Mada, with HarfBuzz's values, and one that variations don't share glyphs requested with other code points
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