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
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>
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—
Taco Hoekwater E: taco@bittext.nl
genderfluid (all pronouns)