Re: Animations in ConTeXt

[Richard Hirsch <richard.hirsch@gmx.net>]

Richard Rascher-Friesenhausen asked
> So again. Is it possible to write something like the above animation
packages 
> in ConTeXt (as a module)?

If Acrobat can display them, ConTeXt can generate them.

Here is a simple example. 

\setupoutput      [pdf]
\setupcolors      [state=start]
\setupinteraction [state=start]
\setuppapersize   [S6][S6]

%% this is just code to get something to animate
\startMPinclusions
  picture thearrow, thestar;

  drawarrow (origin--up) scaled 10mm
    withpen pencircle scaled 3pt
    withcolor .9 red;
  setbounds currentpicture to (fullcircle scaled 22mm);

  thearrow:= currentpicture scaled 5;
  currentpicture:= nullpicture;

  for angle=0 step 72 until 359:
    draw thearrow rotated angle;
  endfor

  thestar:= currentpicture;
  currentpicture:= nullpicture
\stopMPinclusions

\setupMPvariables [drawstar] [rotation=0]
\startuniqueMPgraphic{drawstar}{rotation}
  draw thestar rotated \MPvar{rotation};
\stopuniqueMPgraphic


%% now we define some symbols (the frames of the animated sequence)
\def\definestarsymbol#1{%
  \definesymbol [star #1] [\uniqueMPgraphic{drawstar}{rotation=#1}]}

\definestarsymbol{0}
\definestarsymbol{6}
\definestarsymbol{12}
\definestarsymbol{18}
\definestarsymbol{24}
\definestarsymbol{30}
\definestarsymbol{36}
\definestarsymbol{42}
\definestarsymbol{48}
\definestarsymbol{54}
\definestarsymbol{60}
\definestarsymbol{66}

%% the frames are put into a fieldstack
\definefieldstack [vortex]
  [star 0,  star 6,  star 12, star 18, star 24, star 30, 
   star 36, star 42, star 48, star 54, star 60, star 66]

%% and this is the JavaScrip code that displays the frames one by one
\startJSpreamble MyField used later
var current = 1;
var delay   = 200;              % 200 milliseconds
var timer;
var running = false;            % animation currently not running

function Advance_Angle ( ) {
  this.getField("vortex:"+current).value = "Off";
  if (++current > 12)    % number of frames
    { current = 1; }    % loop through frames
  this.getField("vortex:"+current).value = "On";
}
\stopJSpreamble

%% we want to control the starting and stopping of the animation
\startJScode Rotate_Star uses MyField
if (running) { 
  try { app.clearInterval(timer); } catch(except) {};
  running = false;
}
else { 
  timer = app.setInterval("Advance_Angle()",delay); 
  running = true;
}
\stopJScode


\starttext
  \placefigure [here] [fig:animation]
  {A simple \MetaFun\ animation,
  click \goto {here} [JS(Rotate_Star)] to start (or stop)}
  {\fieldstack [vortex]}
\stoptext

Of course you would want to put the symbol definitions and the
definition of the fieldstack into a loop. I tried 
%% \newcount\angle
%% \angle=0%\zerocount
%% \dorecurse{12} {%
%%    \number\angle:\qquad
%%    \definestarsymbol{\the\angle}
%%    \symbol[star \number\angle]\par
%%    \advance\angle by 6}
and did get the single symbols. I wasn't successful however in putting
the symbol list of the fieldstack definition into a loop. Perhaps the
ConTeXt gurus can help.

Best regards,

  Richard