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

Mojca Miklavec mojca.miklavec.lists at gmail.com
Mon Aug 7 10:04:31 CEST 2006


On 8/7/06, Hans Hagen wrote:
> 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

Thanks! This indeed solves the problem. However, I'm not sure any more
whether blackoutMPgraphic should be true or false by default.

One of my old files (when I was learning metapost from the manual):

def star (expr size, n, pos) =
	for a=0 step 360/n until round(360*(1-1/n)) :
		draw (origin -- (size/2,0))
			rotatedaround (origin,a) shifted pos ;
		endfor ;
enddef ;

beginfig(803) ;
	pickup pencircle scaled 2mm ; star(2cm,5,origin) ;
endfig ;

--------------------------------

\useexternalfigure[pentastar][star.803][height=4cm]
\starttext
\placefigure
{A five||point star drawn by \METAPOST.}
{\color[green]{\externalfigure[pentastar]}} % I wanted it to be green
\stoptext

--------------------------------

I tried that one once more because I remember that I was very happy to
be able to color the star from outside without modifying the figure
itself (I didn't use any explicit color to make it black though).

I don't mind it either way (now that I know how to switch it on or
off), but I'm not sure if there are not other people using the same
trick as well.



The "real problem" appears in the following figure where the first
black is ignored and the second one is not, so it's rather
inconsistent:

\setupcolors
	[state=start,textcolor=blue]
\chardef\blackoutMPgraphic 0

\starttext
\startMPcode
draw \sometxt{blue} withcolor black;
draw \sometxt{red} shifted (1.5cm,0) withcolor red;
draw \sometxt{black} shifted (3cm,0) withcolor black;
\stopMPcode
\stoptext

I can image a "fair solution" to draw "withcolor black" in black and
to let the parts with no explicit color and an empty drawoptions()
string to use the "default color" (perhaps with gsave/grestore). But
I'm not entitled to judge about it.

In any case I'll have to use a solution which will not depend on this
behaviour. Is there any chance to get "withcolor somecolor", where
"somecolor" is the color set with "textcolor=somecolor"?

Thanks a lot,
    Mojca


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