How to define an array of pens

How to define an array of pens

[Otared Kavian]

Hi Hans,

After learning from you how to define an array of colors and paths, I would like to know how is it possible to define a variable pen size.
In the following working example below, I would like to replace 

	MyPens[j] := pencircle scaled 2pt ;

by something like

	MyPens[j] := pencircle scaled (2+j) pt ;

but this does not work (neither do (2+j)*pt). 
Is it possible to specify the pen size according to the value of j, without using a structure like

	if j == -1 :
		MyPens[j] := pencircle scaled 1pt ;
	elseif j == 0 :
		MyPens[j] := pencircle scaled 2pt ;
	else :
		MyPens[j] := pencircle scaled 3pt ;
	fi

(In my real example I have more than three values for j).

%% begin example-array.tex
\startMPpage
	string MyColors[] ;
	path   MyPaths [] ;
	pen MyPens[] ;
	for j = -1 step 1 until 1 :
		MyPens[j] := pencircle scaled 2pt ; % I would like to say here (2+j) pt
	endfor
	MyPaths[-1] := (-1.5cm,1.5cm) -- (1.5cm,1.5cm) ; MyColors[-1] := "magenta" ; 
	MyPaths[0] := (-2cm,2cm) -- (2cm,-2cm) ; MyColors[0] := "darkyellow" ;
	MyPaths[1] := fullcircle scaled 3cm ; MyColors[1] := "darkred" ;
	for j = -1 step 1 until 1 :
		draw MyPaths[j] withpen MyPens[j] withcolor MyColors[j] ;
	endfor
\stopMPpage
%% end example-array.tex

Best regards: Otared
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Re: How to define an array of pens

[Taco Hoekwater]

> On 22 Jun 2020, at 09:17, Otared Kavian <otared@gmail.com> wrote:
> 
> Hi Hans,
> 
> After learning from you how to define an array of colors and paths, I would like to know how is it possible to define a variable pen size.
> In the following working example below, I would like to replace 
> 
> 	MyPens[j] := pencircle scaled 2pt ;
> 
> by something like
> 
> 	MyPens[j] := pencircle scaled (2+j) pt ;

MyPens[j] := pencircle scaled ((2+j)*pt);

“pt” is just a multiplier variable in MetaPost. there is an
implied multiplication operation, but that only works in
bare-number cases. That is why you need 

 (2+j)*pt

The outer parentheses are to prevent MetaPost from interpreting
your line as 

  (pencircle scaled (2+j)) * pt;

Best wishes,
Taco


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maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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Re: How to define an array of pens

[Otared Kavian]

Thanks Taco!
I added this and Hans' explanations to the wiki:

	https://wiki.contextgarden.net/variable_color

but could not set a better title for that page such as « Variable arrays of colors, pens, paths ». 

Best regards: Otared

> On 22 Jun 2020, at 09:28, Taco Hoekwater <taco@elvenkind.com> wrote:
> 
> 
> 
>> On 22 Jun 2020, at 09:17, Otared Kavian <otared@gmail.com> wrote:
>> 
>> Hi Hans,
>> 
>> After learning from you how to define an array of colors and paths, I would like to know how is it possible to define a variable pen size.
>> In the following working example below, I would like to replace 
>> 
>> 	MyPens[j] := pencircle scaled 2pt ;
>> 
>> by something like
>> 
>> 	MyPens[j] := pencircle scaled (2+j) pt ;
> 
> MyPens[j] := pencircle scaled ((2+j)*pt);
> 
> “pt” is just a multiplier variable in MetaPost. there is an
> implied multiplication operation, but that only works in
> bare-number cases. That is why you need 
> 
> (2+j)*pt
> 
> The outer parentheses are to prevent MetaPost from interpreting
> your line as 
> 
>  (pencircle scaled (2+j)) * pt;
> 
> Best wishes,
> Taco
> 
> 
> ___________________________________________________________________________________
> 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://context.aanhet.net
> archive  : https://bitbucket.org/phg/context-mirror/commits/
> wiki     : http://contextgarden.net
> ___________________________________________________________________________________

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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
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___________________________________________________________________________________

Re: How to define an array of pens

[Alan Braslau]

On 22/06/20 01:17, Otared Kavian wrote:
> 	for j = -1 step 1 until 1 :
> 		MyPens[j] := pencircle scaled 2pt ; % I would like to say here (2+j) pt
> 	endfor

MyPens[j] := pencircle scaled (2+j)*pt ;

pt is just a variable, and one can write 2pt implicitly implying the 
multiplication, but must explicitly write (2+j)*pt to parse correctly.

Alan
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