[NTG-context] Labels in MetaPost (MetaObj)

Stefan Müller warrence.stm at gmx.de
Sat Jan 22 14:25:34 CET 2011


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
>
>
>
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>
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