Re: The current state of rendering and overlap

On Tue, Dec 19, 2023 at 11:25 AM Alexei Podtelezhnikov <[email protected]>
wrote:

>
> 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.