This seems to be triggered by the font having variations (an 'fvar' table is present) but no 'gvar' -- it looks like this confuses the Core Text APIs that we rely on, and as soon as any non-default variation values are passed, the glyphs (and advance widths) collapse. Adding an empty 'gvar' table fixes it. As we don't have FreeType in our Mac build as an alternative for rasterizing the glyphs (which I presume is what Blink uses?), maybe we could add an empty 'gvar' during sanitization as a workaround.
Bug 1792214 Comment 3 Edit History
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This seems to be triggered by the font having variations (an 'fvar' table is present) but no 'gvar' -- it looks like this confuses the Core Text APIs that we rely on to get glyph outlines and advances, and as soon as any non-default variation values are passed, the glyphs (and advance widths) collapse. Adding an empty 'gvar' table fixes it. As we don't have FreeType in our Mac build as an alternative for rasterizing the glyphs (which I presume is what Blink uses?), maybe we could add an empty 'gvar' during sanitization as a workaround.