[metapost] Feature Request: Get envelope of path stroked with arbitrary pen

[luigi scarso]

On Fri, Feb 9, 2018 at 1:36 AM,  <mskala at ansuz.sooke.bc.ca> wrote:
> On Thu, 8 Feb 2018, Kevin Keith wrote:
>> It would be of immense use if it were possible to get the path of the
>> outline of some arbitrary pen stroke.
>> Since metapost already outputs bezier curves, instead of bitmaps, it would
>> seem that the machinery to compute the envelope is already in place, so it
>> shouldn't be too difficult to expose this as an operator in the language
>> itself.
>
> I agree this would be nice.  However, I don't think it's so easy to do.
> METATYPE1 (used by the Latin Modern project and my own Tsukurimashou) has
> an implementation in Metapost macros; it usually works, but requires
> handholding, and when it fails it's difficult to debug.  FontForge also
> has an implementation of a similar feature, which has always been buggy
> and a cause of user complaints.  If it were to be a Metapost language
> feature, I hope that the implementation would be at the standard of
> quality and non-bugginess that we expect of "engine" code in the TeX
> ecosystem - and I think algorithms to actually achieve that on the "expand
> stroke" problem may be an open research problem.  Among other issues, the
> envelope of a path defined by cubic splines is not itself a cubic spline,
> so you need to do some approximation, and coming up with rules for how
> close the approximation needs to be, that cover all cases, is difficult.
>
> --
> Matthew Skala
> mskala at ansuz.sooke.bc.ca                 People before principles.
> http://ansuz.sooke.bc.ca/
> --
> http://tug.org/metapost/

I can think about it, but first I need a small set of significant
examples (quite unlikely that I will implement something new for the
next texlive,  btw) .

-- 
luigi