[NTG-context] MetaFun path joiners && and &&&& do not like single point paths

[NTG-context] MetaFun path joiners && and &&&& do not like single point paths

[Gavin via ntg-context]

Hi MetaFun fans,

Following a suggestion of Hans, I experimented with && and &&& and &&&& for joining paths in MetaFun. The joiner &&& produces one long path, but && and &&&& seem to produce a disconnected path which includes all the original paths. However, if one of the paths is a single point, then it connects it. MWE below.

I spotted this on my globes module, where we saw an extra line appear for a very specific orientation of the globe. I guessed that this orientation had an island right on the horizon, so that only one boundary point was visible, creating a singe point path for that island. I should probably fix my module so it doesn’t do that. However, it might be nice to have && and &&&& deal with this situation gracefully.

Gavin


\startMPpage
 path p[], q ;
 p1 = fullcircle scaled 3cm ;
 p2 = fullcircle scaled 2cm shifted (3cm,0) ;
 p3 = (3cm,2cm) ;
 q = for i = 1 upto 3 :
        p[i] &&
     endfor
     cycle ;
 draw p1 withpen pencircle scaled 2pt withcolor .7 ;
 draw p2 withpen pencircle scaled 2pt withcolor .7 ;
 draw p3 withpen pencircle scaled 2pt withcolor .7 ;
 draw q withcolor red ;
 eofill q withcolor 0.9 ;
 draw fullcircle scaled 6cm shifted (1.25cm,0) ;
\stopMPpage
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[NTG-context] Re: MetaFun path joiners && and &&&& do not like single point paths

[Mikael Sundqvist]

Hi

On Sun, Dec 31, 2023 at 3:33 AM Gavin via ntg-context
<ntg-context@ntg.nl> wrote:
>
> Hi MetaFun fans,
>
> Following a suggestion of Hans, I experimented with && and &&& and &&&& for joining paths in MetaFun. The joiner &&& produces one long path, but && and &&&& seem to produce a disconnected path which includes all the original paths. However, if one of the paths is a single point, then it connects it. MWE below.
>
> I spotted this on my globes module, where we saw an extra line appear for a very specific orientation of the globe. I guessed that this orientation had an island right on the horizon, so that only one boundary point was visible, creating a singe point path for that island. I should probably fix my module so it doesn’t do that. However, it might be nice to have && and &&&& deal with this situation gracefully.
>
> Gavin
>
>
> \startMPpage
>  path p[], q ;
>  p1 = fullcircle scaled 3cm ;
>  p2 = fullcircle scaled 2cm shifted (3cm,0) ;
>  p3 = (3cm,2cm) ;
>  q = for i = 1 upto 3 :
>         p[i] &&
>      endfor
>      cycle ;
>  draw p1 withpen pencircle scaled 2pt withcolor .7 ;
>  draw p2 withpen pencircle scaled 2pt withcolor .7 ;
>  draw p3 withpen pencircle scaled 2pt withcolor .7 ;
>  draw q withcolor red ;
>  eofill q withcolor 0.9 ;
>  draw fullcircle scaled 6cm shifted (1.25cm,0) ;
> \stopMPpage

Not beautiful, but this seems to do what you want in this particular case:

\startMPpage
path p[], q ;
p1 = fullcircle scaled 3cm ;
p2 = fullcircle scaled 2cm shifted (3cm,0) ;
p3 = (3cm,2cm) ;
p4 = fullcircle ;
q = p[1] for i = 2 upto 3:
if (length(p[i]) == 0): &&& else: && fi p[i]
endfor
&& cycle ;
eofill q withcolor 0.9 ;
draw p1 withpen pencircle scaled 2pt withcolor .7 ;
draw p2 withpen pencircle scaled 2pt withcolor .7 ;
draw p3 withpen pencircle scaled 2pt withcolor .7 ;
draw q withcolor red ;
draw fullcircle scaled 6cm shifted (1.25cm,0) ;
\stopMPpage

This gives

q = p1 && p2 &&& p3 && cycle ;

/Mikael
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___________________________________________________________________________________

[NTG-context] Re: MetaFun path joiners && and &&&& do not like single point paths

[Hans Hagen via ntg-context]

On 12/31/2023 8:06 AM, Mikael Sundqvist wrote:
> \startMPpage
> path p[], q ;
> p1 = fullcircle scaled 3cm ;
> p2 = fullcircle scaled 2cm shifted (3cm,0) ;
> p3 = (3cm,2cm) ;
> p4 = fullcircle ;
> q = p[1] for i = 2 upto 3:
> if (length(p[i]) == 0): &&& else: && fi p[i]
> endfor
> && cycle ;
> eofill q withcolor 0.9 ;
> draw p1 withpen pencircle scaled 2pt withcolor .7 ;
> draw p2 withpen pencircle scaled 2pt withcolor .7 ;
> draw p3 withpen pencircle scaled 2pt withcolor .7 ;
> draw q withcolor red ;
> draw fullcircle scaled 6cm shifted (1.25cm,0) ;
> \stopMPpage
maybe this is a bit more beautiful then

  q = for i = 1 upto 3 :
     if length(p[i]) == 0 : % todo: a fast nolength
         (p[i] -- p[i] shifted 5(eps,eps))
     else:
         p[i]
     fi &&
  endfor cycle ;

(i'm not sure if we should change the implementation, probably not 
unless we have &&&&& -- actually we could have proper keywords which 
makes it less clumsy. Or 'recycle' that does the ugly eps job when we 
have a zero length path but we can move that over the year boundary.)

Hans

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------

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___________________________________________________________________________________

[NTG-context] Re: MetaFun path joiners && and &&&& do not like single point paths

[Gavin via ntg-context]

Hi Hans and Mikael,

Thanks for your solutions. I’m happy to discard paths that have no area, so I used:

q = for i = 1 upto 3 :
      if (length(p[i]) > 1): p[i] && fi
    endfor
    cycle ;

This worked in the MWE, but it didn’t solve my problem in the globes module. Something else must be happening there. I’ll keep looking.

Gavin
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[NTG-context] Lua and inject.path to make a disconnected MetaPost path?

[Gavin via ntg-context]

Hello LuaMetaFun Fans,

Can I use mp.inject.path in Lua to create a disconnected path in MetaPost?

This is for my module that draws globes. I currently do something like this for drawing the continents. (This MWE has two triangular continents.)

\startluacode
  continents = {}
  continents[1] = {{0,0}, {-1,-1}, {-1,0}, cycle = true }
  continents[2] = {{0,1}, {1,0}, {1,-1}, cycle = true }
  function mp.getglobepath(continentnum)
    mp.inject.path(continents[continentnum])
  end
\stopluacode

\startMPpage
  path p[], q ;
  p1 = (lua.mp.getglobepath(1) scaled 1cm) ;
  p2 = (lua.mp.getglobepath(2) scaled 1cm) ;
  q = p1 && p2 && cycle ;
  draw p1 withpen pencircle scaled 2pt withcolor .7 ;
  draw p2 withpen pencircle scaled 2pt withcolor .7 ;
  fill q withcolor 0.9 ;
  draw q withcolor red ;
\stopMPpage

The path q has both of the continents, disconnected.

I’d like to produce the two continents in Lua and pass them to MetaPost as a single disconnected path, using something like this: 

\startluacode
  continents = {
    {0,0}, {-1,-1}, {-1,0}, — Change this to make a disconnected path!
    {0,1}, {1,0}, {1,-1},
    cycle = true }
  function mp.getglobepath()
    mp.inject.path(continents)
  end
\stopluacode

\startMPpage
  path p ;
  p = (lua.mp.getglobepath() scaled 1cm) ;
  fill p withcolor 0.9 ;
  draw p withcolor red ;
\stopMPpage

If I can make the path p disconnected, this would allow me to make exactly the path I want in Lua, before passing it to MetaPost, rather than passing lots of paths and connecting them in MetaPost with the mysterious (to me) && or &&&&.

Thanks!
Gavin


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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 / https://mailman.ntg.nl/mailman3/lists/ntg-context.ntg.nl
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