Re: [ft-devel] [PATCH v2] Improve FT_Outline_Embolden for the unintended artifacts problem (#45596).

[Byeongsik Jeon]

On Mon, 8 Oct 2018 21:38:42 -0400, Alexei Podtelezhnikov <address@hidden> wrote:
> > I want to hear your opinion on this approach.
>
> The original glyph shape is usually smooth: the contours have no
> self-intersections. The emboldening might result in self-intersecting
> contours. This is the main reason for majority of artifacts. You
> already figured out that corners slide along bisectors, assuming
> symmetric strength.x == strength.y. It is easy to see that self
> intersections happen when a segment flips its orientation under
> certain condition. This condition is easy to formulate but it involves
> both corners at the segment termini and the length of the segment.
> Nothing short of resolving these will work: such segments have to be
> removed. To put it differently, the outline has to be simplified by
> removing self-intersecting segments and replacing them with a point at
> the intersection of the flanking segments. That is it and then you
> apply emboldening cleanly.
Yes. I was trying to do a solution this way. The problem is that this method 
alone can eliminate the intended design of the font.

So, how about using the newly introduced shifter to implement it? k==2.3 is 
almost similar to the existing shifter between 90 and 270 degrees, and I think 
it is appropriate for the rest.

> The other issue is sharp corners that are left. The standard solution
> for them is bevel or round join of lines in the emboldened outline.
> This is totally separate.
>
> I do not see other reasons for artifacts and very much doubt that any
> easier solution exists. By the way, we has glyph stroker
> https://www.freetype.org/freetype2/docs/reference/ft2-glyph_stroker.html.
> This should be a sister algorithm, but it is implemented separately
> with a bunch of trigonometry. I personally would love to have a single
> FreeType module handle both, implemented using bisectors. So this is a
> big project altogether: I would estimate at least 100 hours of
> programing.