Hi Behdad >> >>> Note that freetype does not use the overlap flags to determine the path >>> fill rule (winding vs even-odd), it always uses winding for TT or CFF2 >>> variable fonts, as the spec mandates; the discussion here is about freetype >>> using the (TT glyf only) overlap flags to enable what Alexei calls "4x4 >>> bilevel oversampling" in order to mitigate the effects of increased pixel >>> coverage where paths overlap inside a glyph. I'm just summarizing the above >>> linked fonttools issue, but I don't fully understand the technical details >>> of this rendering technique. >>> CFF2 doesn't have an equivalent mechanism to say "this glyph may contain >>> overlaps", which prompted this specific email thread. >> >>>> CFF was even-odd. CFF2 is non-zero winding. >>>> >> This is about the coverage calculation rather than the fill rule. Suppose >> two contours cover half-pixel each. The integral coverage depends on how >> they overlap over that pixel. The only way to reasonably deal with it is >> oversampling. > > I might be wrong, but I think cairo simplifies the shape, merging the > overlaps.
I think some font tools do that then saving static instances from variable fonts. It is a not easy on the fly.
