[NTG-context] metafun & \sometxt: should black be "black" or "textcolor"?

Hans Hagen pragma at wxs.nl
Mon Aug 7 00:02:15 CEST 2006

Taco Hoekwater wrote:
> Hi Mojca,
>
> Mojca Miklavec wrote:
>
>> But the other \sometxt was indeed red - withcolor seems to work, but
>> only conditionally. And I have some weird examples of two texts one
>> after another. In some cases (if something else is drawn inbetween and
>> a color changed twice), then the second text will be black. But it's
>> quite unpredictable (that one might even be bug in my code, so I don't
>> want to complain before I have an example).
>>
>
> Ok, I looked into this again, and I was definately wrong.
>
> The actual problem appears to be that metapost does not write a
> color switch for 'black' when it appears at the start of a file,
> it simply assumes the start color is black. This could be
> considered a bug in MetaPost or a missing feature in ConTeXt
> (i have not decided yet :-)).
>
> Quick fix: You can start your MP code with an explicit color
> initialization.
>
>    \startMPcode
>       special "0 setgray";
>       ......
>    \stopMPcode
>
>
> A hack, I know. MetaPost should be able to distinguish between
>    draw p
> and
>    draw p withcolor (0,0,0)
> but currently it can't (because the structure is initialized
> as (0,0,0)). It is not quite a bug either, because there may
> well be MP code out there that depends on this.
> In fact, probably code by Knuth, Hobby, Jacko, and Hans ;-)
>
>
in meta-pdf.tex:

\chardef\blackoutMPgraphic\plusone

\def\finishMPgraphic
{\stopMPresources
\egroup
\setbox\scratchbox\vbox
{\forgetall
\hbox
{\PDFcode{q \MPxscale\space 0 0 \MPyscale\space \MPxoffset\space \MPyoffset\space cm}%
\ifcase\blackoutMPgraphic\or\PDFcode{0 g 0 G}\fi
\lower\MPyshift\box\scratchbox % unscaled shift
\PDFcode{Q}}}%
\ht\scratchbox\MPheight
\wd\scratchbox\MPwidth
\dp\scratchbox\zeropoint\relax
\dopackageMPgraphic\scratchbox
\egroup
\endinput}

\starttext

\color[red]{\startMPcode
draw fullcircle scaled 5cm ;
draw btex test etex ;
\stopMPcode red}

\startreusableMPgraphic{test}
draw fullcircle scaled 5cm ;
draw btex test etex ;
\stopreusableMPgraphic

\color[red]{red \reuseMPgraphic{test} red}

\stoptext

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