[NTG-context] Re: Animation using MetaFun

19 Jul 2025

      Hi,

On Sat, Jul 19, 2025 at 2:42 AM Jeong Dal via ntg-context
 wrote:
...
Dear all,
I tried to make an animation which draws Cardioid curve.
I found a code which draws Cardioid using circles.
Since I’d like to draw it differently, I modified it a little.
1. Define the z[] values in the \startMPdefinitions block
2. Modified the drawing method in \startMPbuffer
When I run it, it doesn’t recognize the z[] values defined already.
I think that the z[] values are not delivered to \startbuffer.
I tried \startMPinclusions, \startMPinitialization, but I couldn’t succeed.
1. How can I deliver the z[] values into the buffer?
2. What is wrong in the following code?
Thank you for reading.
Best regards,
Dalyoung
\usemodule[animation]
\setupinteraction[state=start]
\startMPdefinitions%{Cardioid}
path p,q;
numeric u, ang,j,num;
picture pict;
u := 1cm;
ang := 360/52;
p := fullcircle scaled 5u;
for i=0 upto 51:
z[i] = 2.5*dir(ang*i)*u;
endfor;
pict := image (
draw p withpen pencircle scaled 1;
);
\stopMPdefinitions
\startbuffer[Cardioid][s]
draw pict;
num := \MPrawvar{Cardioid}{s};
for i = 0 upto num:
j := 2i mod 52;
draw z[i] -- z[j];
endfor;
setbounds currentpicture to boundingbox currentpicture enlarged 2mm ;
\stopbuffer
\startdocument
\startanimation[menu=yes, framerate=7]
\dorecurse{52}
{\startexpanded
\startframe
\setupMPvariables[Cardioid][s=\recurselevel]
\processMPbuffer[Cardioid]
\stopframe
\stopexpanded}
\stopanimation
\stopdocument
I don't have the animation module, so maybe I miss the point, but the
code below at least compiles and gives something that could be what
you are looking for. If not, sorry for the noise.

% \usemodule[animation]
\setupinteraction[state=start]

\startMPinitializations% CHANGED
path p,q;
numeric u, ang,j,num;
picture pict;

u := 1cm;
ang := 360/52;

p := fullcircle scaled 5u;
for i=0 upto 51:
  z[i] = 2.5*dir(ang*i)*u;
endfor;

z[52]=z[0] ; % NEW

pict := image (
    draw p withpen pencircle scaled 1;
    );
\stopMPinitializations% CHANGED

\startbuffer[Cardioid][s]
  draw pict;
  num := \MPrawvar{Cardioid}{s};

  for i = 0 upto num:
    j := 2i mod 52;
    draw z[i] -- z[j];
  endfor;
  setbounds currentpicture to boundingbox currentpicture enlarged 2mm ;
\stopbuffer

\startdocument

% \startanimation[menu=yes, framerate=7]
\dorecurse{52}
{%\startexpanded
\startframed
\setupMPvariables[Cardioid][s=\recurselevel]
\processMPbuffer[Cardioid]
\stopframed
%\stopexpanded
}
% \stopanimation
\stopdocument

/Mikael

[NTG-context] Re: Animation using MetaFun

Mikael Sundqvist