Labels in MetaPost (MetaObj)

Labels in MetaPost (MetaObj)

[Stefan Müller]

Hi list,

I'm having some trouble with MetaPost in general and MetaObj in 
particular. I hope someone on this list can assist me here. I'm trying 
to run the appended ConTeXt file with a quite simple object "Segment" 
(from the manual [1], section 2.1). This script works fine as it is. I 
wanted to add a simple TeX label ("\tt \overbar{E}") to the drawing 
macro, but failed.

When including the line marked with "% 1" the TeX run fails. I don't 
understand why.

The line with "% 2" is taken frome the metaobj manual (section 5.8) [1], 
but including this doesn't work either.

It would be great if someone could tell me what's wrong with the mp-code 
below and explain how to place a (TeX) label inside a metaobj object.

Thanks in advance,
Stefan.


[1] http://tex.loria.fr/prod-graph/momanual.pdf

PS: Both variants fail with mp error messages like this:

"mplib           > mp terminal: ! Inconsistent equation (off by 1).
<to be read again>
                    ;
assignObj->(SUFFIX0)=incr(nObj_);
 
iname_[(SUFFIX0)]=str(SUFFIX0);addclass_((S...

newSegment->...roup.assignObj((SUFFIX2),"Segment")
 
;ObjPoint.a,b;ObjCode"@##b...
<to be read again>
                    ;
<*> ...ar {E}") shifted n.a; enddef; newSegment.s;
                                                    s.a=origin; 
drawObj(s); ;
! Redundant equation.
<to be read again>
                    ;
assignObj->...bj_);iname_[(SUFFIX0)]=str(SUFFIX0);
 
addclass_((SUFFIX0),(EXPR1...

newSegment->...roup.assignObj((SUFFIX2),"Segment")
 
;ObjPoint.a,b;ObjCode"@##b..."


<=======================================>
\startMPinclusions
	input metaobj;
\stopMPinclusions

\startMPpage
	vardef newSegment@#=
		assignObj(@#,"Segment");
		ObjPoint a,b;
		ObjCode "@#b-@#a=(1cm,2cm)";
	enddef;

	def drawSegment(suffix n)=
		draw n.a--n.b;
%		draw btex \tt \overbar{E} etex shifted n.a; % 1
	enddef;

	newSegment.s;
%	ObjLabel.s(btex hello! etex) "labpoint(a)"; % 2
	s.a=origin;
	drawObj(s);
\stopMPpage
<=======================================>
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Re: Labels in MetaPost (MetaObj)

[Taco Hoekwater]

On 01/18/2011 01:17 PM, Stefan Müller wrote:
> Hi list,
>
> I'm having some trouble with MetaPost in general and MetaObj in
> particular.

The core problem is that context mkiv loads the metapost code twice
when you are typesetting labels, and that causes trouble for metaobj
which does not expect that. Sorry, I do not know of any solution.
Maybe Hans does?

Best wishes,
Taco
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Re: Labels in MetaPost (MetaObj)

[Hans Hagen]

On 20-1-2011 9:59, Taco Hoekwater wrote:
> On 01/18/2011 01:17 PM, Stefan Müller wrote:
>> Hi list,
>>
>> I'm having some trouble with MetaPost in general and MetaObj in
>> particular.
>
> The core problem is that context mkiv loads the metapost code twice
> when you are typesetting labels, and that causes trouble for metaobj
> which does not expect that. Sorry, I do not know of any solution.
> Maybe Hans does?

not immediately

Hans


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Re: Labels in MetaPost (MetaObj)

[Aditya Mahajan]

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On Sat, 22 Jan 2011, Hans Hagen wrote:

> On 20-1-2011 9:59, Taco Hoekwater wrote:
>> On 01/18/2011 01:17 PM, Stefan Müller wrote:
>>> Hi list,
>>> 
>>> I'm having some trouble with MetaPost in general and MetaObj in
>>> particular.
>> 
>> The core problem is that context mkiv loads the metapost code twice
>> when you are typesetting labels, and that causes trouble for metaobj
>> which does not expect that. Sorry, I do not know of any solution.
>> Maybe Hans does?
>
> not immediately

A suggestion: Currently, ConTeXt does not clear the state 
of mplib at the end of each graphic. For example

     \starttext
     \startMPcode
       path p;
       p := fullcircle scaled 4cm ;
     \stopMPcode

     \startMPcode
       draw p ;
     \stopMPcode
     \stoptext

draws a circle. I am not convinced that this is useful. Resetting the state of
mplib after each graphic might be better. Then, after the first run, you could
just set the value of mptopdf.texts[..], reset the state of mplib, and then draw
the graphic in the second run.

This approach will have less surprises. For example, in simpleslides module, we
provide a mechanism for highlighting a part of a picture using arrows. These
arrows are thick (typically 5bp). In order to scale the arrows correctly, we
set:

   autoarrows := true ;

However, in the current implementation, this effect is global. It took a while
to realize that this messed up all the figures with arrows that I was drawing in
a presentation (where autoarrows := false) is better.

Not resetting the mplib state also has advantages. For example, it allows an
easy way to do something on the second path (trivial example, but there are
cases when something like this makes the code much shorter):

     \startMPinclusions[+]
       newboolean flag ;
       flag := false ;
     \stopMPinclusions

     \starttext
     \startMPpage
       if flag :
         fill boundary withcolor 0.5[blue,white] ;
       else :
         path boundary ;
       fi ;

       path A, B;

       A := fullsquare scaled 3cm ;
       B := fullsquare scaled 3cm shifted (5cm,0) ;

       fill A withcolor white ;
       fill B withcolor white ;

       draw A ; draw btex A etex ;
       draw B ; draw btex B etex shifted (5cm,0) ;

       boundary := (boundingbox currentpicture) enlarged 3mm ;

       flag := true ;

     \stopMPpage
     \stoptext

So, perhaps, we can have a `reset` key to \defineMPinstance, and let the user
choose whether to reset after each graphic or not. If `reset=yes` is chosen,
then such errors would not occur.

Aditya

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Re: Labels in MetaPost (MetaObj)

[Stefan Müller]

So its either using text or using metaobj? Too bad, metaobj is quite 
fun... I still hope you guys can fix this, but it's not urgent (to me).

Just as a wild guess I tested the example below today, trying to make 
use of the things Aditya said, but to no avail. Anyway, what does the 
[+] after \startMPinclusions? I did not find documentation for that on 
the wiki.

Best regards,
Stefan.

\startMPinclusions
	input metaobj;
	boolean flag; flag := false;
\stopMPinclusions

\starttext
\startMPpage
	vardef newSegment@\#=
		assignObj(@\#,"Segment");
		ObjPoint a,b;
		ObjCode "@\#b-@\#a=(1cm,2cm)";
	enddef;

	def drawSegment(suffix n)=
		draw n.a--n.b;
	enddef;

	newSegment.s;
	s.a=origin;
	drawObj(s);

	if flag: draw btex A etex; fi;

	flag := true;
\stopMPpage
\stoptext

On 22.01.2011 02:38, Aditya Mahajan wrote:
> On Sat, 22 Jan 2011, Hans Hagen wrote:
>
>> On 20-1-2011 9:59, Taco Hoekwater wrote:
>>> On 01/18/2011 01:17 PM, Stefan Müller wrote:
>>>> Hi list,
>>>>
>>>> I'm having some trouble with MetaPost in general and MetaObj in
>>>> particular.
>>>
>>> The core problem is that context mkiv loads the metapost code twice
>>> when you are typesetting labels, and that causes trouble for metaobj
>>> which does not expect that. Sorry, I do not know of any solution.
>>> Maybe Hans does?
>>
>> not immediately
>
> A suggestion: Currently, ConTeXt does not clear the state of mplib at
> the end of each graphic. For example
>
> \starttext
> \startMPcode
> path p;
> p := fullcircle scaled 4cm ;
> \stopMPcode
>
> \startMPcode
> draw p ;
> \stopMPcode
> \stoptext
>
> draws a circle. I am not convinced that this is useful. Resetting the
> state of
> mplib after each graphic might be better. Then, after the first run, you
> could
> just set the value of mptopdf.texts[..], reset the state of mplib, and
> then draw
> the graphic in the second run.
>
> This approach will have less surprises. For example, in simpleslides
> module, we
> provide a mechanism for highlighting a part of a picture using arrows.
> These
> arrows are thick (typically 5bp). In order to scale the arrows
> correctly, we
> set:
>
> autoarrows := true ;
>
> However, in the current implementation, this effect is global. It took a
> while
> to realize that this messed up all the figures with arrows that I was
> drawing in
> a presentation (where autoarrows := false) is better.
>
> Not resetting the mplib state also has advantages. For example, it
> allows an
> easy way to do something on the second path (trivial example, but there are
> cases when something like this makes the code much shorter):
>
> \startMPinclusions[+]
> newboolean flag ;
> flag := false ;
> \stopMPinclusions
>
> \starttext
> \startMPpage
> if flag :
> fill boundary withcolor 0.5[blue,white] ;
> else :
> path boundary ;
> fi ;
>
> path A, B;
>
> A := fullsquare scaled 3cm ;
> B := fullsquare scaled 3cm shifted (5cm,0) ;
>
> fill A withcolor white ;
> fill B withcolor white ;
>
> draw A ; draw btex A etex ;
> draw B ; draw btex B etex shifted (5cm,0) ;
>
> boundary := (boundingbox currentpicture) enlarged 3mm ;
>
> flag := true ;
>
> \stopMPpage
> \stoptext
>
> So, perhaps, we can have a `reset` key to \defineMPinstance, and let the
> user
> choose whether to reset after each graphic or not. If `reset=yes` is
> chosen,
> then such errors would not occur.
>
> Aditya
>
>
>
> ___________________________________________________________________________________
> 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://tex.aanhet.net
> archive  : http://foundry.supelec.fr/projects/contextrev/
> wiki     : http://contextgarden.net
> ___________________________________________________________________________________
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

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___________________________________________________________________________________

Re: Labels in MetaPost (MetaObj)

[Aditya Mahajan]

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On Sat, 22 Jan 2011, Stefan Müller wrote:

> So its either using text or using metaobj? Too bad, metaobj is quite fun... I 
> still hope you guys can fix this, but it's not urgent (to me).
>
> Anyway, what does the [+] after 
> \startMPinclusions? I did not find documentation for that on the wiki.

\startMPinclusions
   path a ;
\stopMPinclusions

\startMPinclusions
   a := (0,0) -- (1cm,0) ;
\stopMPinclusions

will fail, because the second inclusions overwrites the first. If you use 
[+], then the second inclusions in appended after the first.

> Just as a wild guess I tested the example below today, trying to make use of 
> the things Aditya said, but to no avail.

The trick is to ensure that the offending code (assignObj) is not run 
twice.

\startMPinclusions[+]
   input metaobj;
   boolean flag; flag := false;
\stopMPinclusions

\startMPdefinitions
   vardef newSegment@\#=
     if not flag :
       assignObj(@\#,"Segment");
       ObjPoint a,b;
       ObjCode "@\#b-@\#a=(1cm,2cm)";
     fi ;
   enddef;

   def drawSegment(suffix n)=
     draw n.a--n.b;
     draw btex \tt \overbar{E} etex shifted n.a; % 1
   enddef;
\stopMPdefinitions

\starttext
\startMPpage
   newSegment.s;
   ObjLabel.s(btex hello! etex) "labpoint(a)"; % 2
   s.a=origin;
   drawObj(s);
   flag := true ;
\stopMPpage
\stoptext

@Hans, can we have a `trialtypesetting` for MP code?

Aditya

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Re: Labels in MetaPost (MetaObj)

[Stefan Müller]

On 22.01.2011 17:30, Aditya Mahajan wrote:
> On Sat, 22 Jan 2011, Stefan Müller wrote:
>
>> So its either using text or using metaobj? Too bad, metaobj is quite
>> fun... I still hope you guys can fix this, but it's not urgent (to me).
>>
>> Anyway, what does the [+] after \startMPinclusions? I did not find
>> documentation for that on the wiki.
>
> \startMPinclusions
> path a ;
> \stopMPinclusions
>
> \startMPinclusions
> a := (0,0) -- (1cm,0) ;
> \stopMPinclusions
>
> will fail, because the second inclusions overwrites the first. If you
> use [+], then the second inclusions in appended after the first.

Thank you for the explanation. So if I only have one "inclusions 
section" it doesn't matter?

>> Just as a wild guess I tested the example below today, trying to make
>> use of the things Aditya said, but to no avail.
>
> The trick is to ensure that the offending code (assignObj) is not run
> twice.

Your example works perfect. Many thanks for that as well. I didn't 
realize, that assignObj is causing the trouble, but now it's obvious. 
I'm just curious: the MP-code is only run twice by context if it 
contains labels, right? Otherwise I don't understand why the assignObj 
isn't always failing.

> @Hans, can we have a `trialtypesetting` for MP code?
>
> Aditya

Stefan
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Re: Labels in MetaPost (MetaObj)

[Stefan Müller]

On 23.01.2011 12:40, Stefan Müller wrote:
> On 22.01.2011 17:30, Aditya Mahajan wrote:
>> On Sat, 22 Jan 2011, Stefan Müller wrote:
>>
>>> So its either using text or using metaobj? Too bad, metaobj is quite
>>> fun... I still hope you guys can fix this, but it's not urgent (to me).
>>>
>>> Anyway, what does the [+] after \startMPinclusions? I did not find
>>> documentation for that on the wiki.
>>
>> \startMPinclusions
>> path a ;
>> \stopMPinclusions
>>
>> \startMPinclusions
>> a := (0,0) -- (1cm,0) ;
>> \stopMPinclusions
>>
>> will fail, because the second inclusions overwrites the first. If you
>> use [+], then the second inclusions in appended after the first.
>
> Thank you for the explanation. So if I only have one "inclusions
> section" it doesn't matter?
>
>>> Just as a wild guess I tested the example below today, trying to make
>>> use of the things Aditya said, but to no avail.
>>
>> The trick is to ensure that the offending code (assignObj) is not run
>> twice.
>
> Your example works perfect. Many thanks for that as well. I didn't
> realize, that assignObj is causing the trouble, but now it's obvious.
> I'm just curious: the MP-code is only run twice by context if it
> contains labels, right? Otherwise I don't understand why the assignObj
> isn't always failing.

Sorry for double posting... The method with "if not flag" is a bit 
arkward, because assignObj isn't the only problem. "rotateObj(s, 90)" 
would rotate the object 180 degrees instead of 90; when defining the 
relation between several objects some equations may became redundant (my 
script is rather complex and I'm not sure why some of the equations 
cause trouble).

Stefan
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Re: Labels in MetaPost (MetaObj)

[Aditya Mahajan]

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On Sun, 23 Jan 2011, Stefan Müller wrote:

> Sorry for double posting... The method with "if not flag" is a bit arkward, 
> because assignObj isn't the only problem. "rotateObj(s, 90)" would rotate the 
> object 180 degrees instead of 90; when defining the relation between several 
> objects some equations may became redundant (my script is rather complex and 
> I'm not sure why some of the equations cause trouble).

Depends on the internal implementation of MetaObj (I have not looked at 
that). You can try to iteratively add stuff and see what breaks, and then 
add if not flag around them.

Sorry, but I do not know a more elegant way around this. In the worst 
case, you can switch to MkII to draw your figures :-\

Aditya

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Re: Labels in MetaPost (MetaObj)

[Stefan Müller]

On 23.01.2011 18:22, Aditya Mahajan wrote:
> On Sun, 23 Jan 2011, Stefan Müller wrote:
>
>> Sorry for double posting... The method with "if not flag" is a bit
>> arkward, because assignObj isn't the only problem. "rotateObj(s, 90)"
>> would rotate the object 180 degrees instead of 90; when defining the
>> relation between several objects some equations may became redundant
>> (my script is rather complex and I'm not sure why some of the
>> equations cause trouble).
>
> Depends on the internal implementation of MetaObj (I have not looked at
> that). You can try to iteratively add stuff and see what breaks, and
> then add if not flag around them.

Okay, that's what I do now. It seems it's savest to just put "if not 
flags" around the object constructors, object transformations and 
definition of inter-object relations. This does not produce graphical 
output, so it should be save to run it only once.

> Sorry, but I do not know a more elegant way around this. In the worst
> case, you can switch to MkII to draw your figures :-\
>
> Aditya

Thank you very much!
Stefan.
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Re: Labels in MetaPost (MetaObj)

[Stefan Müller]

Wikified: http://wiki.contextgarden.net/MetaObj_and_Labels
Please update/change as appropriate.

Best regards,
Stefan
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