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How can I test for an open subpath ?

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  How can I test for an open subpath ? Peter Billam <peter@www.pjb.com.au> - 2016-08-25 09:42 +0000
    Re: How can I test for an open subpath ? Carlos <angus@quovadis.com.ar> - 2016-08-25 16:49 +0200
      Re: How can I test for an open subpath ? Peter Billam <peter@www.pjb.com.au> - 2016-08-27 04:28 +0000
      Re: How can I test for an open subpath ? jdaw1 <jdawiseman@gmail.com> - 2016-08-27 10:32 -0700

#2791 — How can I test for an open subpath ?

I find it easy enough to test for existence of a current path, eg:
  { currentpoint } stopped { ...  % no
  } {                pop pop ...  % yes
  } ifelse
(and there may be better ways)

but I'd like to start a procedure with a lineto if there's
a currently open subpath, and with a moveto if there isn't.
Is there a neat way of doing this ?
I can't just use  currentpoint  because it remains defined
after a  closepath;  likewise:
  { gsave lineto grestore } stopped { x0 y0 moveto  % no
  } {                                 x0 y0 lineto  % yes
  } ifelse
messes up for (I think) similar reasons ...  There must be
some neater way than overwriting newpath and closepath ...
Do I have to do forsenics inside pathforall ?

Peter

-- 

Peter Billam    www.pjb.com.au    www.pjb.com.au/comp/contact.html

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#2792

On 25/08/2016 11:42, Peter Billam wrote:
> I find it easy enough to test for existence of a current path, eg:
>    { currentpoint } stopped { ...  % no
>    } {                pop pop ...  % yes
>    } ifelse
> (and there may be better ways)
>
> but I'd like to start a procedure with a lineto if there's
> a currently open subpath, and with a moveto if there isn't.
> Is there a neat way of doing this ?
> I can't just use  currentpoint  because it remains defined
> after a  closepath;  likewise:
>    { gsave lineto grestore } stopped { x0 y0 moveto  % no
>    } {                                 x0 y0 lineto  % yes
>    } ifelse
> messes up for (I think) similar reasons ...  There must be
> some neater way than overwriting newpath and closepath ...
> Do I have to do forsenics inside pathforall ?
>
> Peter
>

It's actually quite simple using pathforall, since one of the procs it 
takes is called specifically on closepath.

/isclosed {
     false
     { pop pop false exch pop }
     { pop pop false exch pop }
     { pop pop pop pop pop pop false exch pop }
     { true exch pop } pathforall
} def

HTH
-- 

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#2793

On 2016-08-25, Carlos <angus@quovadis.com.ar> wrote:
> On 25/08/2016 11:42, Peter Billam wrote:
>> but I'd like to start a procedure with a lineto if there's
>> a currently open subpath, and with a moveto if there isn't.
>> Is there a neat way of doing this ?
>> Do I have to do forsenics inside pathforall ?
> It's actually quite simple using pathforall, since one of
> the procs it takes is called specifically on closepath.
> /isclosed {
>      false
>      { pop pop false exch pop }
>      { pop pop false exch pop }
>      { pop pop pop pop pop pop false exch pop }
>      { true exch pop } pathforall
> } def

Yes, that's neat.  For my use-case I changed the inital false to
true, so that with no current path it would return the same as
after a subpath has been closed, and then I took the liberty
of inverting all the booleans and renaming it is_open_subpath

/is_open_subpath {   % Carlos comp.lang.postscript 20160826 inverted
  false  % except I treat no-currentpath the same as no-open-subpath
  { pop pop true exch pop }
  { pop pop true exch pop }
  { pop pop pop pop pop pop true exch pop }
  { false exch pop } pathforall
} bind def

in which form it appears in
 http://www.pjb.com.au/comp/line_drawing.html#points2curve
 http://www.pjb.com.au/comp/free/line_drawing.ps.txt
 https://github.com/peterbillam/postscriptlib/blob/master/line_drawing.ps
and seems to work well :-) It seems sad to loop through the entire
path just in order to read the last item, but it's only once per
invocation. I'll roll it into other path-segment-constructor procs :-)

Thanks !
Peter

-- 

Peter Billam    www.pjb.com.au    www.pjb.com.au/comp/contact.html

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#2794

On Thursday, 25 August 2016 15:49:46 UTC+1, Carlos  wrote:
> /isclosed {
>      false
>      { pop pop false exch pop }
>      { pop pop false exch pop }
>      { pop pop pop pop pop pop false exch pop }
>      { true exch pop } pathforall
> } def


Slight improvement: replace every “false exch pop” with “pop false”, and “true exch pop” with “pop true”.

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