Re: [ft-devel] [PATCH 1/2] Improve FT_Outline_Embolden for the unintended arfifacts problem (#45597).

[Byeongsik Jeon]

Hi.

> +  det == 0 case:
> +     i.x == i.y == 0, or
> +     o.x == o.y == 0, or
> +     abs( gradient i ) == abs( gradient o )
> +

> +        /* The shift vector is only calculated from the corner type segment.
> +           Other points -- zero length segment, forward straight segment,
> +           wrong forward and backward mixed straight segment -- use this
> +           shift vector as it is. Note the "in.x * out.y - in.y * out.x".
> +
> +           wrong forward and backward mixed straight segment:
> +             one of the causes of unintended artifact generation.
> +         */

It's the segnemts of zero length.
The other problem is the worng frward-backward mixed straight segment (Bauhaus 
'O'). This is abs( gradient i ) == abs (gradient o), or det == 0.


> +        /* The large shift value creates a cross point, which appears
> +           as one of the artifacts. The shift value limitation inhibits
> +           the occurrence of artifacts. */
> +        shift.x = FT_MAX( FT_MIN( shift.x, strength.x ), -strength.x );
> +        shift.y = FT_MAX( FT_MIN( shift.y, strength.y ), -strength.y );
> +

Maybe, it is threshold on the determinant. This inhibits the sarpen corner, and 
the cross point artifacts.


On Thu, 4 Oct 2018 15:29:42 -0400, Alexei Podtelezhnikov <address@hidden> wrote:
> > +  two coalition equation solution:
> > +    det = i.y * o.x - i.x * o.y , det != 0
> > +    shift.x = strength * ( i.x - o.x ) / det
> > +    shift.y = strength * ( i.y - o.y ) / det
>
> So your algorithm is exactly the same as the one implemented
> currently. The tricky part is how you deal with very short collapsing
> segments, the segments of zero length, and your threshold on the
> determinant. Can you please elaborate on that and explain why your
> algorithm is superior?