random background picture in metafun

random background picture in metafun

[Thomas A. Schmitz]

Hi all,

scenario: for a presentation, I want the background to be a random 
picture, taken from a directory "backgroundpics." The pictures are 
numbered consecutively as 1.jpg through 22.jpg. For some complex 
reasons, it would be easier for me to include these pictures via metafun 
(I want to add other graphical elements on top). So my question is, how 
can I pick a random picture? Given the code

StartPage ;
   draw externalfigure "backgoundpics/1" xscaled PaperWidth yscaled 
PaperHeight ;
StopPage ;

how can I obtain a random number and make metapost pick the 
corresponding picture? Sorry, difficult to make a minimal example here...

Thomas
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Re: random background picture in metafun

[Aditya Mahajan]

> Hi all,
>
> scenario: for a presentation, I want the background to be a random picture, 
> taken from a directory "backgroundpics." The pictures are numbered 
> consecutively as 1.jpg through 22.jpg. For some complex reasons, it would be 
> easier for me to include these pictures via metafun (I want to add other 
> graphical elements on top). So my question is, how can I pick a random 
> picture? Given the code
>
> StartPage ;
>  draw externalfigure "backgoundpics/1" xscaled PaperWidth yscaled 
> PaperHeight ;
> StopPage ;
>
> how can I obtain a random number and make metapost pick the corresponding 
> picture? Sorry, difficult to make a minimal example here...

(Untested)

draw externalfigure ("backgroundpics/" & round(uniformdeviate(22)+1))

Aditya
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Re: random background picture in metafun

[Peter Rolf]

Am 13.03.2012 15:45, schrieb Thomas A. Schmitz:
> Hi all,
> 
> scenario: for a presentation, I want the background to be a random
> picture, taken from a directory "backgroundpics." The pictures are
> numbered consecutively as 1.jpg through 22.jpg. For some complex
> reasons, it would be easier for me to include these pictures via metafun
> (I want to add other graphical elements on top). So my question is, how
> can I pick a random picture? Given the code
> 
> StartPage ;
>   draw externalfigure "backgoundpics/1" xscaled PaperWidth yscaled
> PaperHeight ;
> StopPage ;
> 
> how can I obtain a random number and make metapost pick the
> corresponding picture? Sorry, difficult to make a minimal example here...
>
(slightly tested)

string mypath, rndfile;

mypath:= "backgroundpics/";
nofpics:= 22;

n:= round(uniformdeviate(nofpics-1)+1);
rndfile:= mypath & decimal n;


HTH,  Peter


> Thomas
> ___________________________________________________________________________________
> 
> If your question is of interest to others as well, please add an entry
> to the Wiki!
> 
> maillist : ntg-context@ntg.nl /
> http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
> archive  : http://foundry.supelec.fr/projects/contextrev/
> wiki     : http://contextgarden.net
> ___________________________________________________________________________________
> 
> 

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Re: random background picture in metafun

[Thomas A. Schmitz]

On 03/13/2012 05:33 PM, Peter Rolf wrote:
> string mypath, rndfile;
>
> mypath:= "backgroundpics/";
> nofpics:= 22;
>
> n:= round(uniformdeviate(nofpics-1)+1);
> rndfile:= mypath&  decimal n;
>
>
> HTH,  Peter

Aditya, Peter,

thank you both for your quick replies! Peter's works wonderfully; 
Aditya's untested code throws an error "! Not implemented: 
(string)&(known numeric)." I guess this is too arcane for the wiki?

Thanks, and best wishes

Thomas
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Re: random background picture in metafun

[Thomas A. Schmitz]

On 03/13/2012 05:56 PM, Thomas A. Schmitz wrote:
> thank you both for your quick replies! Peter's works wonderfully;
> Aditya's untested code throws an error "! Not implemented:
> (string)&(known numeric)." I guess this is too arcane for the wiki?

To clarify: I wasn't talking about the error, which is pretty clear, but 
about this particular setup - I'm not sure if this is of general 
interest and should be added to the wiki.

Thomas
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Re: random background picture in metafun

[Aditya Mahajan]

On Tue, 13 Mar 2012, Peter Rolf wrote:

> Am 13.03.2012 15:45, schrieb Thomas A. Schmitz:
>> Hi all,
>>
>> scenario: for a presentation, I want the background to be a random
>> picture, taken from a directory "backgroundpics." The pictures are
>> numbered consecutively as 1.jpg through 22.jpg. For some complex
>> reasons, it would be easier for me to include these pictures via metafun
>> (I want to add other graphical elements on top). So my question is, how
>> can I pick a random picture? Given the code
>>
>> StartPage ;
>>   draw externalfigure "backgoundpics/1" xscaled PaperWidth yscaled
>> PaperHeight ;
>> StopPage ;
>>
>> how can I obtain a random number and make metapost pick the
>> corresponding picture? Sorry, difficult to make a minimal example here...
>>
> (slightly tested)
>
> string mypath, rndfile;
>
> mypath:= "backgroundpics/";
> nofpics:= 22;
>
> n:= round(uniformdeviate(nofpics-1)+1);

Actually, round (uniformdeviate(nopics-1)) does not give equal weightage 
to 1 and nofpics. A better solution is

n:= floor(uniformdeviate(nofpics)) + 1;

which gives a uniform weight to all numbers.

> rndfile:= mypath & decimal n;

Aditya
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Re: random background picture in metafun

[Peter Rolf]

Am 13.03.2012 19:00, schrieb Aditya Mahajan:
> On Tue, 13 Mar 2012, Peter Rolf wrote:
> 
>> Am 13.03.2012 15:45, schrieb Thomas A. Schmitz:
>>> Hi all,
>>>
>>> scenario: for a presentation, I want the background to be a random
>>> picture, taken from a directory "backgroundpics." The pictures are
>>> numbered consecutively as 1.jpg through 22.jpg. For some complex
>>> reasons, it would be easier for me to include these pictures via metafun
>>> (I want to add other graphical elements on top). So my question is, how
>>> can I pick a random picture? Given the code
>>>
>>> StartPage ;
>>>   draw externalfigure "backgoundpics/1" xscaled PaperWidth yscaled
>>> PaperHeight ;
>>> StopPage ;
>>>
>>> how can I obtain a random number and make metapost pick the
>>> corresponding picture? Sorry, difficult to make a minimal example
>>> here...
>>>
>> (slightly tested)
>>
>> string mypath, rndfile;
>>
>> mypath:= "backgroundpics/";
>> nofpics:= 22;
>>
>> n:= round(uniformdeviate(nofpics-1)+1);
> 
> Actually, round (uniformdeviate(nopics-1)) does not give equal weightage
> to 1 and nofpics. A better solution is
>
> n:= floor(uniformdeviate(nofpics)) + 1;
> 
:-)

I used 'floor' in my prior tests, but changed it to 'round' because of
the very small chance of getting the highest number (at least with my
formula).

Let's hope, nobody has wikified my bad maths ;-)


> which gives a uniform weight to all numbers.
> 
>> rndfile:= mypath & decimal n;
> 
> Aditya
> ___________________________________________________________________________________
> 
> If your question is of interest to others as well, please add an entry
> to the Wiki!
> 
> maillist : ntg-context@ntg.nl /
> http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
> archive  : http://foundry.supelec.fr/projects/contextrev/
> wiki     : http://contextgarden.net
> ___________________________________________________________________________________
> 
> 

___________________________________________________________________________________
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___________________________________________________________________________________

Re: random background picture in metafun

[Thomas A. Schmitz]

On 03/13/2012 07:24 PM, Peter Rolf wrote:
>> Actually, round (uniformdeviate(nopics-1)) does not give equal weightage
>> >  to 1 and nofpics. A better solution is
>> >
>> >  n:= floor(uniformdeviate(nofpics)) + 1;
>> >
> :-)
>
> I used 'floor' in my prior tests, but changed it to 'round' because of
> the very small chance of getting the highest number (at least with my
> formula).
>
> Let's hope, nobody has wikified my bad maths;-)
>
>
>> >  which gives a uniform weight to all numbers.

Hmm, I absolutely stink at math, but after a few days of testing: the 
"randomness" is a bit disappointing. All my presentations start more or 
less with the same set of background pictures, and since most have < 22 
slides, some slides never come up in the rotation. Is there a way to 
provide metafun with a random seed, say the decimal digit of pi 
corresponding to the rounded number of my cpu's temperature (just 
kidding)? Or maybe a lua solution would be nice, metafun seems to be a 
bit to conservative in its choice of random numbers...

Thomas
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Re: random background picture in metafun

[Hans Hagen]

On 15-3-2012 10:18, Thomas A. Schmitz wrote:
> On 03/13/2012 07:24 PM, Peter Rolf wrote:
>>> Actually, round (uniformdeviate(nopics-1)) does not give equal weightage
>>> > to 1 and nofpics. A better solution is
>>> >
>>> > n:= floor(uniformdeviate(nofpics)) + 1;
>>> >
>> :-)
>>
>> I used 'floor' in my prior tests, but changed it to 'round' because of
>> the very small chance of getting the highest number (at least with my
>> formula).
>>
>> Let's hope, nobody has wikified my bad maths;-)
>>
>>
>>> > which gives a uniform weight to all numbers.
>
> Hmm, I absolutely stink at math, but after a few days of testing: the
> "randomness" is a bit disappointing. All my presentations start more or
> less with the same set of background pictures, and since most have < 22
> slides, some slides never come up in the rotation. Is there a way to
> provide metafun with a random seed, say the decimal digit of pi
> corresponding to the rounded number of my cpu's temperature (just
> kidding)? Or maybe a lua solution would be nice, metafun seems to be a
> bit to conservative in its choice of random numbers...

Ah, but keep in mind that the random number is stored in the tuc file! 
So, as long as that file is not wiped, you get the same random number 
initialization. Imagine what would happen if we would not do that. So, 
just erase the tuc if you want another seed.

Hans

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Re: random background picture in metafun

[Thomas A. Schmitz]

On 03/15/2012 07:06 PM, Hans Hagen wrote:

>
> Ah, but keep in mind that the random number is stored in the tuc file!
> So, as long as that file is not wiped, you get the same random number
> initialization. Imagine what would happen if we would not do that. So,
> just erase the tuc if you want another seed.

Oops, yes of course, that makes sense - all presentations are generated 
from the same xml file, so the tuc never changes! After deleting it, I 
get more of the desired randomness - thanks a lot for the pointer!

All best

Thomas
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