[NTG-context] Help with Metapopst code

[NTG-context] Help with Metapopst code

[Shiv Shankar Dayal]

Hi,

Consider following code:

vardef polygon_with_side(expr n, s) =
save a, b, r; numeric a, b, r;
a * n = 360; a + 2b = 180; r = s * sind(b) / sind(a);
for i = 0 upto n-1: (0, r) rotated (a * i) -- endfor cycle
enddef;

beginfig(1);
path p; p = polygon_with_side(21, 20);
draw p;
endfig;
bye;

It draws a polygon with 21 sides with radius 20. I understand all of
it except the for loop.

What is (0, r) rotated (a *i) doing?

-- 
Respect,
Shiv Shankar Dayal
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[NTG-context] Re: Help with Metapopst code

[Shiv Shankar Dayal]

I think it works like (0, r) rotated (a) -- (0, r) rotated (a * 2) --
... (0, r) rotated (a*20) -- cycle

Is my understanding correct? Also, how can I label these vertices in a for loop?

On Wed, Aug 28, 2024 at 2:25 PM Shiv Shankar Dayal
<shivshankar.dayal@gmail.com> wrote:
>
> Hi,
>
> Consider following code:
>
> vardef polygon_with_side(expr n, s) =
> save a, b, r; numeric a, b, r;
> a * n = 360; a + 2b = 180; r = s * sind(b) / sind(a);
> for i = 0 upto n-1: (0, r) rotated (a * i) -- endfor cycle
> enddef;
>
> beginfig(1);
> path p; p = polygon_with_side(21, 20);
> draw p;
> endfig;
> bye;
>
> It draws a polygon with 21 sides with radius 20. I understand all of
> it except the for loop.
>
> What is (0, r) rotated (a *i) doing?
>
> --
> Respect,
> Shiv Shankar Dayal



-- 
Respect,
Shiv Shankar Dayal
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___________________________________________________________________________________

[NTG-context] Re: Help with Metapopst code

[Mikael Sundqvist]

Hi,

I don't know where you found the code, but the answer to "What is (0,
r) rotated (a *i) doing?" is that it takes the point (0,r) and rotates
it a*i degrees.

For your labeling problem, see the last example of section 2.9 of

https://www.pragma-ade.com/general/manuals/metafun-p.pdf

/Mikael

PS Please do not cross post here and on stackexchange (at least not
without telling).

On Wed, Aug 28, 2024 at 11:12 AM Shiv Shankar Dayal
<shivshankar.dayal@gmail.com> wrote:
>
> I think it works like (0, r) rotated (a) -- (0, r) rotated (a * 2) --
> ... (0, r) rotated (a*20) -- cycle
>
> Is my understanding correct? Also, how can I label these vertices in a for loop?
>
> On Wed, Aug 28, 2024 at 2:25 PM Shiv Shankar Dayal
> <shivshankar.dayal@gmail.com> wrote:
> >
> > Hi,
> >
> > Consider following code:
> >
> > vardef polygon_with_side(expr n, s) =
> > save a, b, r; numeric a, b, r;
> > a * n = 360; a + 2b = 180; r = s * sind(b) / sind(a);
> > for i = 0 upto n-1: (0, r) rotated (a * i) -- endfor cycle
> > enddef;
> >
> > beginfig(1);
> > path p; p = polygon_with_side(21, 20);
> > draw p;
> > endfig;
> > bye;
> >
> > It draws a polygon with 21 sides with radius 20. I understand all of
> > it except the for loop.
> >
> > What is (0, r) rotated (a *i) doing?
> >
> > --
> > Respect,
> > Shiv Shankar Dayal
>
>
>
> --
> Respect,
> Shiv Shankar Dayal
> ___________________________________________________________________________________
> 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!

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___________________________________________________________________________________

[NTG-context] Re: Help with Metapopst code

[Shiv Shankar Dayal]

> I don't know where you found the code, but the answer to "What is (0,
> r) rotated (a *i) doing?" is that it takes the point (0,r) and rotates
> it a*i degrees.

I do not understand the concept of rotating a point. It is rotated with respect
to what reference?

>
> For your labeling problem, see the last example of section 2.9 of
>
> https://www.pragma-ade.com/general/manuals/metafun-p.pdf
>

Thanks, I am reading that.

> /Mikael
>
> PS Please do not cross post here and on stackexchange (at least not
> without telling).
>

I will keep this in mind.

-- 
Respect,
Shiv Shankar Dayal
___________________________________________________________________________________
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___________________________________________________________________________________

[NTG-context] Re: Help with Metapopst code

[Wolfgang Schuster]

Shiv Shankar Dayal schrieb am 28.08.2024 um 12:23:
>> I don't know where you found the code, but the answer to "What is (0,
>> r) rotated (a *i) doing?" is that it takes the point (0,r) and rotates
>> it a*i degrees.
> 
> I do not understand the concept of rotating a point. It is rotated with respect
> to what reference?

You rotate around a point with the x and y coordinates 0.

The blue dot shows the point with the coordinates 0. The green dot is 
rotated around this point.

\starttext

\startMPcode
drawdot (0,0) withpen pencircle scaled 5mm withcolor blue;
draw fullsquare scaled (4cm) withcolor red;
\stopMPcode

\startMPcode
drawdot (0,0) withpen pencircle scaled 5mm withcolor blue;
drawdot (1.5cm,0) withpen pencircle scaled 5mm withcolor green;
draw fullsquare scaled (4cm) withcolor red;
\stopMPcode

\startMPcode
drawdot (0,0) withpen pencircle scaled 5mm withcolor blue;
drawdot (1.5cm,0) rotated (30) withpen pencircle scaled 5mm withcolor green;
draw fullsquare scaled (4cm) withcolor red;
\stopMPcode

\startMPcode
drawdot (0,0) withpen pencircle scaled 5mm withcolor blue;
drawdot (1.5cm,0) rotated (60) withpen pencircle scaled 5mm withcolor green;
draw fullsquare scaled (4cm) withcolor red;
\stopMPcode

\startMPcode
drawdot (0,0) withpen pencircle scaled 5mm withcolor blue;
drawdot (1.5cm,0) rotated (90) withpen pencircle scaled 5mm withcolor green;
draw fullsquare scaled (4cm) withcolor red;
\stopMPcode

\stoptext

Wolfgang
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[NTG-context] Re: Help with Metapopst code

[Mikael Sundqvist]

It is rotated with respect to the origin (that is (0,0)).

If you want to rotate around another point you have rotatedaround.


/Mikael

On Wed, Aug 28, 2024 at 12:27 PM Shiv Shankar Dayal
<shivshankar.dayal@gmail.com> wrote:
>
> > I don't know where you found the code, but the answer to "What is (0,
> > r) rotated (a *i) doing?" is that it takes the point (0,r) and rotates
> > it a*i degrees.
>
> I do not understand the concept of rotating a point. It is rotated with respect
> to what reference?
>
> >
> > For your labeling problem, see the last example of section 2.9 of
> >
> > https://www.pragma-ade.com/general/manuals/metafun-p.pdf
> >
>
> Thanks, I am reading that.
>
> > /Mikael
> >
> > PS Please do not cross post here and on stackexchange (at least not
> > without telling).
> >
>
> I will keep this in mind.
>
> --
> Respect,
> Shiv Shankar Dayal
> ___________________________________________________________________________________
> 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
webpage  : https://www.pragma-ade.nl / https://context.aanhet.net (mirror)
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wiki     : https://wiki.contextgarden.net
___________________________________________________________________________________