Dear Otared,

> 
> Regarding the way Aditya uses \startuseMPgraphic, it is also very instructive. 
> Dalyoung, can you also share the animation example for the foldings ? I am sure we are a few on the list to learn something…
> 

1. Here is the working sample of animation using \processMPbuffer which I did before. You can see it using adobe reader.


\startbuffer[UDBasic]
  pair A,B,C,D;
  pair E, F, G, H;
  path p,q;
  numeric ang,maxNum;
  u:=1in;
  A=(.95*TextWidth,u); B=(0,u); C=(0,0); D=(.95*TextWidth,0);
  p := A--B--C--D;
  q := (TextWidth,1.5u)--(0,1.5u)--(0,-.5u)--(TextWidth,-.5u)--cycle;
  z0=(.1u,0);
  
   vardef nextPt (expr M,N) = 
   if ypart(N) = 0: 
       H := whatever[N, N + dir(.5*angle(M-N))*u] = whatever[A,B];
   else:
       H := whatever[N, N + dir(.5*angle(M-N))*u] = whatever[C,D];
   fi;
   H
   enddef;

   def grayUD(expr i) =
      draw G -- if ypart(B)=ypart(G): B -- C else: C -- B fi --z[i];
      filldraw z[i]+2*(G-z[i])*u -- z[i] -- z[i+1] -- z[i+1]+(G-z[i])*u -- cycle withcolor .75white; 
      draw G -- z[i+1] dashed evenly;
      draw z[0] for k=0 upto i: --z[k] endfor dashed evenly;
      clip currentpicture to q;
      setbounds currentpicture to boundingbox q;
   enddef;

   def linesUD(expr i) =
      draw p;
      draw z0 for k=0 upto i+1: --z[k] endfor dashed evenly;
      setbounds currentpicture to boundingbox q;
   enddef;
\stopbuffer

\startbuffer[UDpts]
   ang := 40;
   z[1] = whatever[z[0], z[0]+dir(ang)*u] = whatever[A,B];
   G := whatever[z[0], z[0]+dir(2*ang)*u] = whatever[A,B];
   for k = 2 upto 20:
      z[k] = nextPt(z[k-2],z[k-1]);
      maxNum := k;
      exitif xpart(z[k]) > TextWidth;
   endfor;
\stopbuffer
\startbuffer[UD0]
   draw p;
   setbounds currentpicture to boundingbox q;
\stopbuffer
\startbuffer[UD1]
   grayUD(0);
\stopbuffer
\startbuffer[UD11]
   linesUD(0);
\stopbuffer
\startbuffer[UD2]
   G := z0;
   grayUD(1)
\stopbuffer
\startbuffer[UD21]
   linesUD(1);
\stopbuffer
\startbuffer[UD3]
   G := z1;
   grayUD(2);
\stopbuffer
\startbuffer[UD31]
   linesUD(2);
\stopbuffer
\startbuffer[UD4]
   G := z2;
   grayUD(3);
\stopbuffer
\startbuffer[UD41]
   linesUD(3);
\stopbuffer
\startbuffer[UD5]
   G := z3;
   grayUD(4);
\stopbuffer
\startbuffer[UD51]
   linesUD(4);
\stopbuffer
\startbuffer[UDFinal]
draw p;
draw z0--z1--z2--z3--z4--z5--z6--z7--z8 dashed evenly;
setbounds currentpicture to boundingbox q;
\stopbuffer

\setupinteraction[state=start]
\usemodule[animation]
\starttext
\startanimation[menu=yes]
{\processMPbuffer[UDBasic,UDpts,UD0]}
{\processMPbuffer[UDBasic,UDpts,UD1]}
{\processMPbuffer[UDBasic,UDpts,UD11]}
{\processMPbuffer[UDBasic,UDpts,UD2]}
{\processMPbuffer[UDBasic,UDpts,UD21]}
{\processMPbuffer[UDBasic,UDpts,UD3]}
{\processMPbuffer[UDBasic,UDpts,UD31]}
{\processMPbuffer[UDBasic,UDpts,UD4]}
{\processMPbuffer[UDBasic,UDpts,UD41]}
{\processMPbuffer[UDBasic,UDpts,UD5]}
{\processMPbuffer[UDBasic,UDpts,UD51]}
{\processMPbuffer[UDBasic,UDpts,UDFinal]}
\stopanimation
\stoptext

Now, I am trying to do the same thing using \startuseMPgraphic, but I don’t the correct result yet.
Using \startuseMPgraphic, and \dorecurse, the code is simpler. But, it seems to me that \startanimation … \stopanimation is not working with \dorecurse{}{} …
It just list all the graphics.
Any hint is welcome.

\startMPinitializations%{UDBasic}
  pair A,B,C,D;
  pair E, F, G, H;
  path p,q;
  numeric ang,maxNum;

  numeric n; %AM Added

  u:=1in;
  A=(.95*TextWidth,u); B=(0,u); C=(0,0); D=(.95*TextWidth,0);
  p := A--B--C--D;
  q := (TextWidth,1.5u)--(0,1.5u)--(0,-.5u)--(TextWidth,-.5u)--cycle;
  z0=(.1u,0);
  
   vardef nextPt (expr M,N) = 
   if ypart(N) = 0: 
       H := whatever[N, N + dir(.5*angle(M-N))*u] = whatever[A,B];
   else:
       H := whatever[N, N + dir(.5*angle(M-N))*u] = whatever[C,D];
   fi;
   H
   enddef;

   def grayUD(expr i) =
      draw G -- if ypart(B)=ypart(G): B -- C else: C -- B fi --z[i];
      filldraw z[i]+2*(G-z[i])*u -- z[i] -- z[i+1] -- z[i+1]+(G-z[i])*u -- cycle withcolor .75white; 
      draw G -- z[i+1] dashed evenly;
      draw z[0] for k=0 upto i: --z[k] endfor dashed evenly;
      clip currentpicture to q;
   enddef;

   def linesUD(expr i) =
      draw p;
      draw z0 for k=0 upto i+1: --z[k] endfor dashed evenly;

      % AM: removed. Set in in the main code
      % setbounds currentpicture to boundingbox q;
   enddef;

   ang := 40;
   z[1] = whatever[z[0], z[0]+dir(ang)*u] = whatever[A,B];

   % AM: Changed next line from G to z[-1]
   z[-1] = whatever[z[0], z[0]+dir(2*ang)*u] = whatever[A,B];
   for k = 2 upto 20:
      z[k] = nextPt(z[k-2],z[k-1]);
      maxNum := k;
      exitif xpart(z[k]) > TextWidth;
   endfor;

\stopMPinitializations

\startuseMPgraphic{foldUD}{num}
   numeric n;
   n := \MPvar{num}-1;
   G := z[n-1];
   grayUD(n);
\stopuseMPgraphic
\startuseMPgraphic{dotLines}{num}
   numeric n;
   n := \MPvar{num}-1;
   linesUD(n);
\stopuseMPgraphic

\setupinteraction[state=start]
\usemodule[animation]
\starttext
\startanimation[menu=yes]
\dorecurse{7}
{
 {\useMPgraphic{foldUD}{num=\recurselevel}}
 {\useMPgraphic{dotLines}{num=\recurselevel}}
}
\stopanimation
\stoptext

Best regards,

Dalyoung