Re: [Freetype-devel] Re: GSOC - Distance Fields

[Alexei Podtelezhnikov]

On Fri, Aug 7, 2020 at 12:54 AM Anuj Verma <anujv@iitbhilai.ac.in> wrote:
>
> Hello Alexei,
>
> > Can you describe discontinuities with the same sign if I overlook them?
>
> So, I found there are two types of discontinuities due to overlapping 
> contours:
>
> A) Discontinuity in sign. (i.e. there is a sudden jump from negative to 
> positive)
> B) Discontinuity in distances. (i.e. the points that should be at 
> infinity/spread have smaller distances)

Yeah. We should basically think of overlaying or combining two
distance fields, generated independently one for each contour.
Has this been discussed in the literature?

> Also, I looked at a library (msdfgen) which handles overlapping contours 
> without
> removing the overlaps. It works well, but it doesn't work for 
> self-intersecting contours,
> that is why I'm not sure whether it's worth implementing.

Self intersecting contours should never and hopefully will never be
allowed in fonts.

> Finally, I can find and fix signs such that all points inside a shape are 
> positive and
> all points outside are negative. But I don't know how I can fix the incorrect 
> distances
> caused by the overlaps. Here is one final example: 
> https://i.imgur.com/jiaqiBS.png
> In this the point `P' has a positive sign and it points to a line inside the 
> shape, which
> is not correct, instead it should point to the corner. Moreover there is no 
> corner in the
> shape because they are two separate contours, so I think removing the 
> overlaps is
> the best way to handle this.

Here I concede we will never find proper distance unless we define the
intersection point.

Alexei