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 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

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