Hi,

It is fun fact very easy to do. You just use \startMPpage (…) \stopMPpage 
multiple times. Here is an example which build an animation of a particle 
moving according to a Brownian motion. 

Fabrice.

% 8< -----------------------------------------------

\usecolors[crayola]
\setupMPinstance

\starttext

% We can put in the inclusions the material we will use at each page, to 
declare things only one time.
\startMPinclusions
 % the frame of the video ;
 path TheFrame ;
 TheFrame := fullsquare scaled 5in ;

 randomseed := 53 ;
 path TheBrownianMotion ;
 pair Coordinate[];
 Coordinate[0] := (0,0);
 TheBrownianMotion := Coordinate[0] ;
 variance := 10 ;
\stopMPinclusions

\dorecurse{600}{ % Frame

\setupMPpage[background=color, backgroundcolor=SpringGreen]
\startMPpage[pagestate=start]

 currentime := #1 ;
 % Just for learning :
 draw TheFrame withpen pencircle scaled .1in withcolor magenta ;
 draw textext("T="&decimal(currentime)) scaled 2 shifted(0,2in) withcolor 
magenta ;

Coordinate[currentime] := Coordinate[currentime-1] + 
%(normaldeviate*variance,normaldeviate*variance) ;
  ((uniformdeviate(1)-0.5)*variance,(uniformdeviate(1)-0.5)*variance) ;
TheBrownianMotion := for p=0 upto (currentime-1) :
  Coordinate[p] .. endfor Coordinate[currentime] ;

draw TheBrownianMotion withpen pencircle scaled .01in withcolor blue ;
draw Coordinate[currentime] withpen pencircle scaled .10in withcolor red ;

setbounds currentpicture to TheFrame ;

desiredformat := 1080;% In pixels (will be converted by default at 72dpi)
currentpicture := currentpicture xysized (desiredformat ,desiredformat );

\stopMPpage

} 

\stoptext
% 8< -----------------------------------------------



> Le 27 nov. 2023 à 13:49, Emanuel Han via ntg-context <ntg-context@ntg.nl> a 
> écrit :
> 
> How can I achieve multipage metapost output from ConTeXt? The result should 
> be a multipage pdf. It contains just a metapost graphic per page. The graphic 
> has always the same bounding box and evolves from page to page: Some elements 
> to be drawn are added, and some others would ideally also be removed, while 
> keeping elements which has already been drawn on previous pages. I can manage 
> when it is not possible to remove elements (in that case I'll just cover them 
> with a covering element).
> 
> I saw that it is possible to achieve my goal with standalone metapost, as 
> described here: 
> https://tex.stackexchange.com/questions/471662/mptopdf-is-multipage-output-pdf-possible
> But I'll need to achieve this with Metapost inside ConTeXt because I use 
> labels in Metapost which print text in Japanese, Korean , Arabic and Roman 
> script: Thanks to ConTeXt, I can define appropriate fonts for each script. 
> All this works already in my working example.
> 
> The only unsolved problem is to ship out multiple pages.
> 
> For the minimal working example, I didn't remove the font defining part, 
> because having 4 different fonts is a condition of my use case. The graphic 
> on the other hand is some simple dummy nonsense graphic not from my project. 
> The graphic is in the provided example drawn as a summing up of layered 
> drawing steps (6 steps, to be precise), so no removing is implemented here 
> (because I don't know how that would be done). If each of the figures 1 to 6 
> of my mwe can be put alone on a page, I'd be already very happy. Now, they're 
> put on top of each other all on the same single page, also on top of figure 0.
> 
> The desired multipage pdf will be used in presentation mode of a pdf viewer 
> and skipped forward and backward from page to page (that is from drawing step 
> to drawing step).
> 
> mwe:
> 
> \enableregime[utf] % enable unicoded input
> 
> \definefontfamily [RomanFont] [rm] [calluna]
> 
> \definefontfamily [KoreanFont] [rm] [applemyungjo]
> 
> \definefontfamily [JapaneseFont] [rm] [hannotatesc]
> 
> \definefontfeature
>  [fea]
>  [mode=node,language=dflt,script=arab,
>   init=yes,
>   medi=yes,
>   fina=yes,
>   isol=yes,
>   calt=yes,
>   rlig=yes,
>   tlig=yes,
>   trep=yes,
>   curs=yes,
>   kern=yes,
>   mark=yes
> ]
> 
> \starttypescript [serif] [notonaskharabic]
>  \definefontsynonym [notonaskharabic-Light]       [name:notonaskharabic]      
>   [features=fea]
>  \definefontsynonym [notonaskharabic-Bold]        [name:notonaskharabic]      
>   [features=fea]
>  \definefontsynonym [notonaskharabic-Italic]      [name:notonaskharabic]      
>   [features=fea]
>  \definefontsynonym [notonaskharabic-Bold-Italic] [name:notonaskharabic]      
>   [features=fea]
> \stoptypescript
> 
> \starttypescript [serif] [notonaskharabic]
>  \usetypescript[serif][fallback]
>  \definefontsynonym [Serif]                       [notonaskharabic-Light]     
>   [features=fea]
>  \definefontsynonym [SerifItalic]                 [notonaskharabic-Italic]    
>   [features=fea]
>  \definefontsynonym [SerifBold]                   [notonaskharabic-Bold]      
>   [features=fea]
>  \definefontsynonym [SerifBoldItalic]             
> [notonaskharabic-Bold-Italic] [features=fea]
> \stoptypescript
> 
> \starttypescript [notonaskharabic]
>   \definetypeface [notonaskharabic] [rm] [serif] [notonaskharabic] [default]
> \stoptypescript
> 
> \usetypescript[notonaskharabic]
> 
> \setupbodyfont [RomanFont]
>    
> 
> \starttext
> 
> \startMPcode
> 
> picture p[];
> path bb; %bounding box
> 
>  z0 = (0,0);   
>  z1 = (60,40);
>  z2 = (40,90); 
>  z3 = (10,70);
>  z4 = (30,50);
>  z5 = (90,70);
>  z6 = (-10,70);
> 
> path A; A = z0..z1..z2..z3..z4 ;
> pair AStartPoint; AStartPoint = point 0 of A;
> pair AEndPoint; AEndPoint = point 4 of A;
> path B; B =  z5..z6;
> pair BStartPoint; BStartPoint = point 0 of B;
> pair BEndPoint; BEndPoint = point 1 of B;
> path C; C = AStartPoint..AEndPoint;
> 
> % drawing steps:       
> p1:=image(
>     draw A withcolor red;
> );
> 
> p2:=image(
>     label(textext("\JapaneseFont 日本語"), AEndPoint);
> );
> 
> p3:=image(
>     label(textext("\notonaskharabic \textdir TRT دانگ") scaled 1.2, 
> AStartPoint);
> );
> 
> p4:=image(
>     label(textext("\KoreanFont 한국어"), BStartPoint);
> );
> 
> p5:=image(
>     label(textext("\RomanFont bāng"), BEndPoint);
>     draw C withcolor green;
> );
> 
> p6:=image(
>     draw B withcolor blue;
> );
> 
> 
> beginfig(0); %% the whole picture for the common bbox
> for k=1 upto 6: draw p[k]; endfor
> bb:=bbox(currentpicture);
> endfig;
>  
> for $=1 upto 6:
> beginfig($);
> for k=1 upto $: draw p[k]; endfor
> setbounds currentpicture  to bb;
> endfig;
> endfor
>  
> \stopMPcode
> \stoptext
> 
> 
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to the 
> Wiki!
> 
> maillist : ntg-context@ntg.nl / 
> https://mailman.ntg.nl/mailman3/lists/ntg-context.ntg.nl
> webpage  : https://www.pragma-ade.nl / https://context.aanhet.net (mirror)
> archive  : https://github.com/contextgarden/context
> wiki     : https://wiki.contextgarden.net
> ___________________________________________________________________________________

___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the 
Wiki!

maillist : ntg-context@ntg.nl / 
https://mailman.ntg.nl/mailman3/lists/ntg-context.ntg.nl
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archive  : https://github.com/contextgarden/context
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