[NTG-context] MetaPost label direction prefix

Hans Hagen pragma at wxs.nl
Sat Aug 24 02:28:34 CEST 2013


On 8/23/2013 3:14 PM, Marco Patzer wrote:
> On 2013–08–23 Hans Hagen wrote:
>
>>> Is this prefix required? It breaks old code and required a branch in
>>> every new project. And I don't really see a reason for this
>>> incompatibility. Here is an example defining a new direction “foo”:
>>
>> The MpIV code has namespace protection. Why run traditional in MkIV?
>>
>>
>>> \starttext
>>>    \startMPcode
>>>      label("first", origin);
>>>
>>>      %% MkIV
>>>      %% pair mfun_laboff.foo ; mfun_laboff.foo := (.5,-1) ;
>>>      %% mfun_labxf.foo := mfun_labyf.foo := 1 ;
>>>
>>>      %% MkII
>>>      pair laboff.foo ; laboff.foo := (.5,-1) ;
>>>      labxf.foo := labyf.foo := 1 ;
>>>
>>>      label.foo("second", origin);
>>>    \stopMPcode
>>> \stoptext
>>
>> I wasn't aware of users defining extra ones. I'll add this:
>
> Probably not many users will tinker with custom label directions,
> but MetaPost package authors do. Some packages like piechartmp¹
> internally use laboff.foo and the mpfun_ prefix breaks those
> packages. They work in traditional MetaPost, plain TeX, LaTeX and
> ConTeXt MkII, but since mplib uses the mpfun_ prefix, those packages
> are broken in MkIV.

that kind of tinkering can also result in overloading context 'extensions'

>> […]
>>      installlabel.foo ( 0, 1, 1, (.5,-1) ) ;
>
> This does not fix the problem since it only *defines* the correct
> variant, it doesn't help *using* those values. If the label values
> are being changed in the package one still has to branch out to
> support both variants. And even if there was an abstraction
> assisting to *use* the laboff values, all MetaPost packages
> tinkering with laboff would need to be adjusted. I can't imagine
> that to happen. Here's what the piechartmp package is doing, for
> instance:

I'll provide:

\starttext
   \startMPcode

     startplaincompatibity ;

         label("first", origin);

         pair laboff.foo ; laboff.foo := (.5,-1) ;
         labxf.foo := labyf.foo := 1 ;

         label.foo("second", origin);

     stopplaincompatibity ;

   \stopMPcode
\stoptext

As I wouldn't be surprised if there were more differences we need to 
handle.

Hans

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