> Le 18 juill. 2022 à 12:31, Hans Hagen via ntg-context <ntg-context@ntg.nl> a
> écrit :
>
> On 7/18/2022 3:20 PM, Fabrice L via ntg-context wrote:
>> Dear list,
>> I’m doing animations in MetaFun, by simply using \startMPpage (…)
>> \stopMPpage for each frame of the animation. Here is an example:
>> https://youtu.be/yhxUbVQx9Uo (please note you can watch it in HD by
>> adjusting the setting in YouTube).
>> This works usually great, but when the number of objects to draw by page is
>> large, the resulting pdf file could be huge, several gigabytes sometimes.
>> Such huge files are difficult (sometimes impossible) to convert in jpeg
>> files (I’m using Image magick for the conversion), necessary to do a mp4
>> movie.
>> One solution is to do several pdf files, for example one by second; with
>> this option, I can do 60 files of 30 pages, for an animation of 60 seconds
>> (1800 frames for 1 minute). Everything is smoother this way, quicker to
>> convert files. But in order to do so, I have to be able to describe each
>> frame of the animation with the same set of instructions; so the position of
>> an object at time t is described by an equation for example.
>> But this is not always possible. If the animation is based on a random
>> process, the position of an object at time t depends on his position at time
>> t-1. I can still use this preceeding strategy by simulating the past at the
>> begging of each second, starting with a unique random seed. So for example
>> if I work on second 9, I begin by calculating the past from frame 1 to frame
>> 240 (8*30) and then simulate time 241, draw frame 241, simulate time 242,
>> draw time 242, etc.. This could be complicated to do, but is feasible. The
>> drawback is that more I advance in time, the more computations I have to do
>> at the beginning of each file.
>> So to simplify things, one option would be to be save the state of some
>> variables at some point in time, say t, in order to be able to access these
>> informations at time t+1. So the strategy would be :
>> % File second1.pdf
>> for frame =1 to 30 :
>> simulate position of objects ;
>> draw the frame ;
>> endfor;
>> save the position of all objects ;
>> % File second2.pdf
>> Read (access) the position of all objects from second 1(after frame 30);
>> for frame =31 to 60 :
>> simulate position of objects ;
>> draw the frame ;
>> endfor;
>> save the position of all objects ;
>> Etc...
>> Does someone has an idea of how to do such a thing ? I can read text file in
>> Context with no problem and integrate them in the animation process with
>> \startMPinclusions (…) \stopMPinclusions, but I did not find a way to write
>> information from MetaFun to a text file. Is Lua the solution ?
> there's always an idea ...
Great ! And thanks…
Of course, it takes me some time to understand, and a little reading in the
metafun xl manual, but now I catch it !
>
> \starttext
> \startMPpage
> runscript("metapost.setparameterset('test', table.load('mydata.lua') or {
> })") ;
> path b ; b := getparameterpath "test" "test_c";
> draw fullcircle scaled 3cm ;
> draw b scaled .4;
> % show(b);
> getparameters "test" [
> test_a = 123,
> test_b = (456,789),
> test_c = (boundingbox currentpicture)
> ] ;
> runscript("table.save('mydata.lua',(metapost.getparameterset('test')))") ;
> \stopMPpage
> \stoptext
>
> but maybe i need abetter one .. a proper save/restore in the tuc file or so,
> but you can play with this first
>
> Hans
If someones in the futur needs more explanation (like me!), here is my minimal
working example derived from the one of Hans:
First page, we assign a value to the pair « ThePosition[2] », write the value
in a file (« TheMagicalFile.lua »), change the value in memory in the second
page, and then read it from the external file in the third page. Of course, it
works ! And this could run in separates process of course.
% ————————————
\starttext
\startMPpage
pair ThePosition[];
ThePosition[1] := (0,0) ;
ThePosition[2] := (10,10) ;
draw ThePosition[1] -- ThePosition[2] ;
% save the parameters in the object MyData
getparameters "MyData" [
pos_a = ThePosition[1],
pos_b = ThePosition[2]
] ;
% Save this object in a file
runscript("table.save('TheMagicalFile.lua',(metapost.getparameterset('MyData')))")
;
\stopMPpage
% We modify the value of ThePosition[2]
\startMPpage
ThePosition[2] := (10,0) ;
draw ThePosition[1] -- ThePosition[2] ;
\stopMPpage
% We now read the value of ThePosition[2] from the file
\startMPpage
% Save the data from the external file
runscript("metapost.setparameterset('MyData', table.load('TheMagicalFile.lua')
or { })") ;
ThePosition[2] := getparameter "MyData" "pos_b" ;
draw ThePosition[1] -- ThePosition[2] ;
\stopMPpage
\stoptext
% ————————————
Complementary question : I saw that the « pos_a » « pos_b » of the example
could not take numerical value, for example pos_1, pos_2.. How can I use
metafun to write a macro to save the contents of hundreds of variable in this
object, something like :
getparameters "MyData » [
for i=1 upto 100 :
pos_decimal(i) = ThePosition[i],
endfor ;
] ;
If this is possible, then this is wonderful and open news doors !
Thanks again,
Fabrice.
>
>
> -----------------------------------------------------------------
> Hans Hagen | PRAGMA ADE
> Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
> tel: 038 477 53 69 | www.pragma-ade.nl <http://www.pragma-ade.nl/> |
> www.pragma-pod.nl <http://www.pragma-pod.nl/>
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