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Saving currentpoint and CTM

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  Saving currentpoint and CTM Andre Majorel <cheney@halliburton.com> - 2016-05-20 16:28 +0000
    Re: Saving currentpoint and CTM luser- -droog <mijoryx@yahoo.com> - 2016-05-20 11:52 -0700
      Re: Saving currentpoint and CTM luser- -droog <mijoryx@yahoo.com> - 2016-05-20 11:55 -0700
    Re: Saving currentpoint and CTM Carlos <angus@quovadis.com.ar> - 2016-05-20 22:58 +0200
      Re: Saving currentpoint and CTM Andre Majorel <cheney@halliburton.com> - 2016-05-21 17:52 +0000
    Re: Saving currentpoint and CTM jdaw1 <jdawiseman@gmail.com> - 2016-05-21 05:55 -0700

#2576 — Saving currentpoint and CTM

Is there a way to save (and later restore) currentpoint and the
CTM, so that after restoring, you can resume adding to the path
as if no moves or rotations had happened since you saved ?

Rather not use gsave/grestore because
1. it saves and restores more things than I want, such as the path,
2. it is saved on the stack and I would prefer a dictionary of
   arrays or something like that which would give me the freedom
   of saving multiple times and restoring in any order without
   burdening my feeble brain.

Thanks in advance.

-- 
André Majorel http://www.teaser.fr/~amajorel/
J'ai des vrais problèmes, vous avez des faux problèmes.

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#2577

On Friday, May 20, 2016 at 11:28:03 AM UTC-5, Andre Majorel wrote:
> Is there a way to save (and later restore) currentpoint and the
> CTM, so that after restoring, you can resume adding to the path
> as if no moves or rotations had happened since you saved ?
> 
> Rather not use gsave/grestore because
> 1. it saves and restores more things than I want, such as the path,
> 2. it is saved on the stack and I would prefer a dictionary of
>    arrays or something like that which would give me the freedom
>    of saving multiple times and restoring in any order without
>    burdening my feeble brain.
> 
> Thanks in advance.
> 

A couple of approaches you could look into.

You could use save/restore instead of gsave/grestore. These return
a 'save token' object and you can restore to any save-point by 
using the appropriate token. In a sense you cannot restore "in any
order" because restoring to a lower save-point will invalidate
any higher-level tokens (if they're stored as definitions, then
the definitions should safely vanish upon restoring to the lower
level).

You could use user-paths. I don't fully understand how they work,
but they let you treat paths more like objects.

Create your own path objects. You can dump a path to a procedure
with something like:

    [
    {/moveto cvx}
    {/lineto cvx}
    {/curveto cvx}
    {/closepath cvx}
    pathforall ] cvx

To add a matrix, add something like

    matrix currentmatrix /setmatrix cvx

after the first `[`. Then you can recreate the
same path by exec'ing this procedure.

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#2578

On Friday, May 20, 2016 at 1:52:50 PM UTC-5, luser- -droog wrote:
> On Friday, May 20, 2016 at 11:28:03 AM UTC-5, Andre Majorel wrote:
> > Is there a way to save (and later restore) currentpoint and the
> > CTM, so that after restoring, you can resume adding to the path
> > as if no moves or rotations had happened since you saved ?
> > 
> > Rather not use gsave/grestore because
> > 1. it saves and restores more things than I want, such as the path,
> > 2. it is saved on the stack and I would prefer a dictionary of
> >    arrays or something like that which would give me the freedom
> >    of saving multiple times and restoring in any order without
> >    burdening my feeble brain.
> > 
> > Thanks in advance.
> > 
> 
> A couple of approaches you could look into.
> 
> You could use save/restore instead of gsave/grestore. These return
> a 'save token' object and you can restore to any save-point by 
> using the appropriate token. In a sense you cannot restore "in any
> order" because restoring to a lower save-point will invalidate
> any higher-level tokens (if they're stored as definitions, then
> the definitions should safely vanish upon restoring to the lower
> level).
> 

This is probably even worse from the perspective of "saving more
than I want". :(

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#2579

[Andre Majorel <cheney@halliburton.com>, 2016-05-20 16:28]
> Is there a way to save (and later restore) currentpoint and the
> CTM, so that after restoring, you can resume adding to the path
> as if no moves or rotations had happened since you saved ?
> 
> Rather not use gsave/grestore because
> 1. it saves and restores more things than I want, such as the path,
> 2. it is saved on the stack and I would prefer a dictionary of
>    arrays or something like that which would give me the freedom
>    of saving multiple times and restoring in any order without
>    burdening my feeble brain.
> 
> Thanks in advance.
> 

Do you mean something like this?

  /savepos { [ currentpoint 6 array currentmatrix ] } def
  /restorepos { aload pop setmatrix moveto } def

E.g.,

 100 100 moveto 100 0 rlineto /x savepos def
 0 20 260 { x restorepos  rotate  50 0 rlineto } for
 showpage

-- 

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#2583

On 2016-05-20, Carlos <angus@quovadis.com.ar> wrote:
> [Andre Majorel <cheney@halliburton.com>, 2016-05-20 16:28]
>> Is there a way to save (and later restore) currentpoint and the
>> CTM, so that after restoring, you can resume adding to the path
>> as if no moves or rotations had happened since you saved ?
>> 
>> Rather not use gsave/grestore because
>> 1. it saves and restores more things than I want, such as the path,
>> 2. it is saved on the stack and I would prefer a dictionary of
>>    arrays or something like that which would give me the freedom
>>    of saving multiple times and restoring in any order without
>>    burdening my feeble brain.
>
> Do you mean something like this?
>
>   /savepos { [ currentpoint 6 array currentmatrix ] } def
>   /restorepos { aload pop setmatrix moveto } def
>
> E.g.,
>
>  100 100 moveto 100 0 rlineto /x savepos def
>  0 20 260 { x restorepos  rotate  50 0 rlineto } for
>  showpage

With you making it so simple, I feel stupid for not working it
out myself.

Yes, that it exactly what I wanted. Thanks everyone.

-- 
André Majorel http://www.teaser.fr/~amajorel/
J'ai des vrais problèmes, vous avez des faux problèmes.

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#2582

Do you want to save the whole path, or just its end, the currentpoint? 

currentpoint matrix currentmatrix 
… % lots of stuff 
setmatrix newpath moveto

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