Re: envelope

Hans Hagen <[email protected]>
Newsgroups gmane.comp.tex.metapost
Message-ID <[email protected]> 
On 9/15/2016 8:27 PM, Daniel H. Luecking wrote:
> Nicola:
>
> The syntax is
>    envelope <polygonal pen> of <path primary>
>
> For example,
>   path p;
>   p := envelope pensquare of (up--left);
>
> It returns the path which, when filled, produces the effect of stroking
> the pen along the path. Elliptical pens (e.g., pencircle) produce an error.
>
> Stroking an elliptical pen is simply passed on to PostScript. But polygonal
> pens (inherited from metafont) require this as a workaround.
>
> I deduced this by a little trial and error based on some descriptions in
> the web source mp.w.

Here's what happens in the result.


\starttext

\startMPpage
draw envelope pensquare of (up--left) ;
\stopMPpage

% 0.500000000 w
% 0.500000000 0.500000000 m
% 0.500000000 0.500000000 0.500000000 1.500000000 0.500000000 1.500000000 c
% 0.500000000 1.500000000 -0.500000000 1.500000000 -0.500000000 
1.500000000 c
% -1.500000000 0.500000000 l
% -1.500000000 0.500000000 -1.500000000 -0.500000000 -1.500000000 
-0.500000000 c
% -1.500000000 -0.500000000 -0.500000000 -0.500000000 -0.500000000 
-0.500000000 c
% 0.500000000 0.500000000 l
% h S

\startMPpage
draw (up--left) withpen pensquare ;
\stopMPpage

% 0.500000000 0.500000000 m
% 0.500000000 0.500000000 0.500000000 1.500000000 0.500000000 1.500000000 c
% 0.500000000 1.500000000 -0.500000000 1.500000000 -0.500000000 
1.500000000 c
% -1.500000000 0.500000000 l
% -1.500000000 0.500000000 -1.500000000 -0.500000000 -1.500000000 
-0.500000000 c
% -1.500000000 -0.500000000 -0.500000000 -0.500000000 -0.500000000 
-0.500000000 c
% 0.500000000 0.500000000 l
% h f

\startMPpage
draw fullcircle ;
\stopMPpage

% 0.500000000 w
% 0.500000000 0 m
% 0.500000000 0.132614136 0.447311401 0.259780884 0.353546143 0.353546143 c
% 0.259780884 0.447311401 0.132614136 0.500000000 0 0.500000000 c
% -0.132614136 0.500000000 -0.259780884 0.447311401 -0.353546143 
0.353546143 c
% -0.447311401 0.259780884 -0.500000000 0.132614136 -0.500000000 0 c
% -0.500000000 -0.132614136 -0.447311401 -0.259780884 -0.353546143 
-0.353546143 c
% -0.259780884 -0.447311401 -0.132614136 -0.500000000 0 -0.500000000 c
% 0.132614136 -0.500000000 0.259780884 -0.447311401 0.353546143 
-0.353546143 c
% 0.447311401 -0.259780884 0.500000000 -0.132614136 0.500000000 0 c
% h S

\startMPpage
draw envelope pensquare of fullcircle ;
\stopMPpage

% 0.500000000 w
% 1 0.500000000 m
% 1 0.632614136 0.947311401 0.759780884 0.853546143 0.853546143 c
% 0.759780884 0.947311401 0.632614136 1 0.500000000 1 c
% 0.500000000 1 -0.500000000 1 -0.500000000 1 c
% -0.500000000 1 l
% -0.632614136 1 -0.759780884 0.947311401 -0.853546143 0.853546143 c
% -0.947311401 0.759780884 -1 0.632614136 -1 0.500000000 c
% -1 0.500000000 -1 -0.500000000 -1 -0.500000000 c
% -1 -0.500000000 l
% -1 -0.632614136 -0.947311401 -0.759780884 -0.853546143 -0.853546143 c
% -0.759780884 -0.947311401 -0.632614136 -1 -0.500000000 -1 c
% -0.500000000 -1 0.500000000 -1 0.500000000 -1 c
% 0.500000000 -1 l
% 0.632614136 -1 0.759780884 -0.947311401 0.853546143 -0.853546143 c
% 0.947311401 -0.759780884 1 -0.632614136 1 -0.500000000 c
% 1 -0.500000000 1 0.500000000 1 0.500000000 c
% 1 0.500000000 l
% h S

\startMPpage
draw fullcircle withpen pensquare ;
\stopMPpage

% 0 -0.500000000 m
% 0 -0.500000000 1 -0.500000000 1 -0.500000000 c
% 1 -0.500000000 1 0.500000000 1 0.500000000 c
% 1 0.632614136 0.947311401 0.759780884 0.853546143 0.853546143 c
% 0.759780884 0.947311401 0.632614136 1 0.500000000 1 c
% 0.500000000 1 -0.500000000 1 -0.500000000 1 c
% -0.500000000 1 l
% -0.632614136 1 -0.759780884 0.947311401 -0.853546143 0.853546143 c
% -0.947311401 0.759780884 -1 0.632614136 -1 0.500000000 c
% -1 0.500000000 -1 -0.500000000 -1 -0.500000000 c
% -1 -0.500000000 l
% -1 -0.632614136 -0.947311401 -0.759780884 -0.853546143 -0.853546143 c
% -0.759780884 -0.947311401 -0.632614136 -1 -0.500000000 -1 c
% -0.500000000 -1 0.500000000 -1 0.500000000 -1 c
% 0.500000000 -1 l
% 0.632614136 -1 0.759780884 -0.947311401 0.853546143 -0.853546143 c
% 0.947311401 -0.759780884 1 -0.632614136 1 -0.500000000 c
% 1 -0.500000000 1 0.500000000 1 0.500000000 c
% 1 0.500000000 l
% 1 0.500000000 0 0.500000000 0 0.500000000 c
% 0 0.367385864 -0.052688599 0.240219116 -0.146453857 0.146453857 c
% -0.240219116 0.052688599 -0.367385864 0 -0.500000000 0 c
% -0.500000000 0 0.500000000 0 0.500000000 0 c
% 0.367385864 0 0.240219116 0.052688599 0.146453857 0.146453857 c
% 0.052688599 0.240219116 0 0.367385864 0 0.500000000 c
% 0 0.500000000 l
% 0 0.500000000 0 -0.500000000 0 -0.500000000 c
% 0 -0.367385864 0.052688599 -0.240219116 0.146453857 -0.146453857 c
% 0.240219116 -0.052688599 0.367385864 0 0.500000000 0 c
% 0.500000000 0 l
% 0.500000000 0 -0.500000000 0 -0.500000000 0 c
% -0.367385864 0 -0.240219116 -0.052688599 -0.146453857 -0.146453857 c
% -0.052688599 -0.240219116 0 -0.367385864 0 -0.500000000 c
% h f

\startMPpage
draw fullcircle withpen pensquare ;
\stopMPpage

% 0 -0.500000000 m
% 0 -0.500000000 1 -0.500000000 1 -0.500000000 c
% 1 -0.500000000 1 0.500000000 1 0.500000000 c
% 1 0.632614136 0.947311401 0.759780884 0.853546143 0.853546143 c
% 0.759780884 0.947311401 0.632614136 1 0.500000000 1 c
% 0.500000000 1 -0.500000000 1 -0.500000000 1 c
% -0.500000000 1 l
% -0.632614136 1 -0.759780884 0.947311401 -0.853546143 0.853546143 c
% -0.947311401 0.759780884 -1 0.632614136 -1 0.500000000 c
% -1 0.500000000 -1 -0.500000000 -1 -0.500000000 c
% -1 -0.500000000 l
% -1 -0.632614136 -0.947311401 -0.759780884 -0.853546143 -0.853546143 c
% -0.759780884 -0.947311401 -0.632614136 -1 -0.500000000 -1 c
% -0.500000000 -1 0.500000000 -1 0.500000000 -1 c
% 0.500000000 -1 l
% 0.632614136 -1 0.759780884 -0.947311401 0.853546143 -0.853546143 c
% 0.947311401 -0.759780884 1 -0.632614136 1 -0.500000000 c
% 1 -0.500000000 1 0.500000000 1 0.500000000 c
% 1 0.500000000 l
% 1 0.500000000 0 0.500000000 0 0.500000000 c
% 0 0.367385864 -0.052688599 0.240219116 -0.146453857 0.146453857 c
% -0.240219116 0.052688599 -0.367385864 0 -0.500000000 0 c
% -0.500000000 0 0.500000000 0 0.500000000 0 c
% 0.367385864 0 0.240219116 0.052688599 0.146453857 0.146453857 c
% 0.052688599 0.240219116 0 0.367385864 0 0.500000000 c
% 0 0.500000000 l
% 0 0.500000000 0 -0.500000000 0 -0.500000000 c
% 0 -0.367385864 0.052688599 -0.240219116 0.146453857 -0.146453857 c
% 0.240219116 -0.052688599 0.367385864 0 0.500000000 0 c
% 0.500000000 0 l
% 0.500000000 0 -0.500000000 0 -0.500000000 0 c
% -0.367385864 0 -0.240219116 -0.052688599 -0.146453857 -0.146453857 c
% -0.052688599 -0.240219116 0 -0.367385864 0 -0.500000000 c
% h f

\startMPpage
draw fullcircle withpen pencircle ;
\stopMPpage

% 1 w
% 0.500000000 0 m
% 0.500000000 0.132614136 0.447311401 0.259780884 0.353546143 0.353546143 c
% 0.259780884 0.447311401 0.132614136 0.500000000 0 0.500000000 c
% -0.132614136 0.500000000 -0.259780884 0.447311401 -0.353546143 
0.353546143 c
% -0.447311401 0.259780884 -0.500000000 0.132614136 -0.500000000 0 c
% -0.500000000 -0.132614136 -0.447311401 -0.259780884 -0.353546143 
-0.353546143 c
% -0.259780884 -0.447311401 -0.132614136 -0.500000000 0 -0.500000000 c
% 0.132614136 -0.500000000 0.259780884 -0.447311401 0.353546143 
-0.353546143 c
% 0.447311401 -0.259780884 0.500000000 -0.132614136 0.500000000 0 c
% h S

\stoptext




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