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

[Alexei Podtelezhnikov]

On Sun, Jun 28, 2020 at 10:18 AM Anuj Verma <anujv@iitbhilai.ac.in> wrote:
> Apart from that, I thought about another optimization:
> Smooth rasterizer is ultra fast, it only takes a few nano-
> seconds to render. So we can embolden the outline by
> spread, render it with the smooth or monochrome rasterizer
> and that will give us all the points that we need to check. It
> can pair up well with the bounding box method.

Unfortunately, the emboldening algorithm has flaws... The stroker is
probably a bit more reliable but is much slower too.

The smooth renderer performance is a good benchmark to aspire to and I
think that the SDF renderer can be within reach. The distance to a
line is a cross product divided by the line length ignoring the
distances to the ends for a moment. The division by the length is the
same for all grid points in the neighborhood so it can be reused as
inverse length. The cross products are also interesting: they turn out
to be incremental from grid to grid point. Combining the two facts, it
is super fast to fill the neighborhood of a line using a single
division. Now you just have to deal with the ends trivially. That is
why I think that ultimately dividing the curves will win and the
performance will be comparable to the smooth renderer.

Best,
Alexei