Hi Taco,

thanks for your help. This works for me!
On Jan. 5 2024, at 2:13 pm, Taco Hoekwater <taco@bittext.nl> wrote:
> Hi,
>
> Here is 'a' way to draw the subpath, at least. I do not have time to come up with a nice “thicker in the middle” solution.
> Best wishes,
> Taco
>
>
> \startMPcode
> numeric u; u=1cm;
> %equiangular spiral
> numeric a, k ;
> a = 2.3; %scaling factor
> k = 8.61722335;
> path S;
> S = right for t=1 upto 360: .. a ** (t/50.2) * dir (-k*t) endfor;
> draw S;
>
> z1 = 8 dir -14;
> path A; A = origin -- z1 scaled 0.7u ;% draw A;
> pair AEndPoint; AEndPoint = point 1 of A;
> pair gong[], times; numeric n; n = 0;
> numeric gongtimes[]; % new
> for i = 1 upto length(A):
> for j = 1 upto length(S):
> times := subpath (i-1,i) of A intersectiontimes subpath (j-1,j) of S;
> if xpart times > -1:
> gong[incr n] = 1[point xpart times of subpath (i-1,i) of A,
> point ypart times of subpath (j-1,j) of S];
> gongtimes[n] = j-1 + ypart times; % new
> fi
> endfor
> endfor
>
> % new
> path H; H = subpath(gongtimes[6],gongtimes[7]) of S;
> lH = length(H);
> for i = 1 upto 100:
> draw (subpath((i-1)/100*lH, i/100* lH) of H) withcolor red withpen (pencircle scaled(abs(abs(i-50)-50)/10)) ;
> endfor;
>
> \stopMPcode
>
> > On 5 Jan 2024, at 09:56, Emanuel Han via ntg-context <ntg-context@ntg.nl> wrote:
> >
> > Hi all,
> >
> > I have this MWE. Now I want to draw only the subpath of S between gong6 and gong7 with a red line which is narrower at the two ends and thicker in the middle part. How to achieve this?
> >
> > Thanks!
> > Emanuel
> >
> > \setuppapersize[A4,landscape]
> >
> > \starttext
> >
> > \startMPcode
> > numeric u; u=1cm;
> > %equiangular spiral
> > numeric a, k ;
> > a = 2.3; %scaling factor
> > k = 8.61722335;
> > path S;
> > S = right for t=1 upto 360: .. a ** (t/50.2) * dir (-k*t) endfor;
> > draw S;
> >
> > z1 = 8 dir -14;
> > path A; A = origin -- z1 scaled 0.7u ; draw A;
> > pair AEndPoint; AEndPoint = point 1 of A;
> > pair gong[], times; numeric n; n = 0;
> > for i = 1 upto length(A):
> > for j = 1 upto length(S):
> > times := subpath (i-1,i) of A intersectiontimes subpath (j-1,j) of S;
> > if xpart times > -1:
> > gong[incr n] = 1/2[point xpart times of subpath (i-1,i) of A,
> > point ypart times of subpath (j-1,j) of S];
> > fi
> > endfor
> > endfor
> >
> > dotlabel.rt ("$gong6$", gong6);
> > dotlabel.rt ("$gong7$", gong7);
> >
> > %Now I want to draw only the subpath of S between gong6 and gong7 with a red line which is narrower at the two ends and thicker in the middle part
> >
> > \stopMPcode
> >
> > \stoptext
> > ___________________________________________________________________________________
> > If your question is of interest to others as well, please add an entry to the Wiki!
> >
> > maillist : ntg-context@ntg.nl / https://mailman.ntg.nl/mailman3/lists/ntg-context.ntg.nl
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> > archive : https://github.com/contextgarden/context
> > wiki : https://wiki.contextgarden.net
> > ___________________________________________________________________________________
>
> —
> Taco Hoekwater E: taco@bittext.nl
> genderfluid (all pronouns)
>