Re: Ampersand in Metapost

[Marco <netuse@lavabit.com>]

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On Fri, 14 May 2010 00:37:44 +0200, Mojca Miklavec
<mojca.miklavec.lists@gmail.com> wrote:

> On Thu, May 13, 2010 at 23:45, Marco <netuse@lavabit.com> wrote:
> > On Thu, 13 May 2010 22:58:46 +0200, Hans Hagen <pragma@wxs.nl>
> > wrote:
> >> On 13-5-2010 9:18, Marco wrote:
> >> > Hi,
> >> >
> >> > I have a problem producing an ampersand in metapost. In ConTeXt
> >> > it works as expected. Have a look at the following example.
> >> >
> >> > \starttext
> >> > \&  % OK
> >> > \startMPcode
> >> > label(textext("\&"),origin); % produces error
> >> > \stopMPcode
> >> > \stoptext
> >> >
> >> > The compile time error message is as follows:
> >> >    ! Misplaced alignment tab character&.
> >> >    l.1 \MPLIBsettext{1}{&
> >>
> >> \letterpercent
> > Doesn't work. I suppose you mean \letterampersand. If I change \&
> > into \letterampersand I get exactly the same error as \& produces
> > (BTW: \letterpercent also produces an error, but a different one).
> 
> So:
> - label(textext("\letterbackslash\letterampersand"),origin);
> - label(textext("\letterbackslash\&"),origin);
This both works. Thanks, Mojca.

> This is because the commands are interpreted with TeX before they are
> written to mpgraph.mp. The \letterampersand or \& generates the
> character & alone: you need to preceed it with backslash, so that
> metapost finally knows what to do.
That sound like a double-escape. Intuitionally one would simply use &. I know,
TeX doesn't like this, so we escape it, \&. However MetaPost doesn't like
this, so we add a second escape: \letterbackslash\&. That's OK, as I rarely
need ampersands in my graphics.

> PS: I would say: better use \sometxt which is far more reliable unless
> you have to use textext to do string manipulation.
I don't know exactly which transformations are considered as »string
manipulation«. I've read your MyWay on \sometxt. Brilliant piece of doc. But
I've three questions.

   i) Is it about MkII, MkIV or both?
  ii) Is it still up-to-date?
 iii) Why should I better use \sometxt?

What do you mean by »more reliable«? After having read your MyWay I would say
that textext is more reliable because it can do dynamic text.

I created a testfile to compare textext and \sometxt. The points to compare
were those you mentionend in your MyWay as advantages of \sometxt. The
testfile »t.tex« is attached. I processed it with

ConTeXt  ver: 2010.05.08
luatex, version beta-0.60.1-2010042821

Here are my results:

-There is one obvious reason: speed

    $ for i in `seq 5`; do context -mode=textext t | tail -1; done
    MTXrun | total runtime: 128.008
    MTXrun | total runtime: 37.893
    MTXrun | total runtime: 37.900
    MTXrun | total runtime: 38.391
    MTXrun | total runtime: 38.029
    $ rm t.{log,pdf,tuc}
    $ for i in `seq 5`; do context -mode=sometxt t | tail -1; done
    MTXrun | total runtime: 127.195
    MTXrun | total runtime: 40.131
    MTXrun | total runtime: 41.071
    MTXrun | total runtime: 37.424
    MTXrun | total runtime: 39.121

Average runtime:
    textext  variant: 56s
    \sometxt variant: 57s

That is the same. Maybe my test file is not appropriate to test the speed. I'm
sure you have performed more advanced tests.

-Document-wide definitions are seen
  [...] definitions with arguments will fail to work. 

The first line, a document-wide definition with arguments works in both
versions.

-Problems with expansion
  [...]  as far as I remember math expressions (fractions perhaps) never
  worked as they were supposed to

The second definition is a math expressions with fractions. It seems to work.

-Less characters to escape

Yes, that's the topic of this thread. I don't know, I didn't check. The only
check I performed was the ampersand and it needs the same workaround using
\letterbackslash as textext.

I know, your MyWay is old. Maybe some things are fixed now. But I don't see
many advantages for me using it.

In fact, I have a problem getting random colors working. Take the following
example (taken from my earlier thread).

% This line is needed to get »withcolor« to work?
\chardef\TeXtextcolormode\zerocount

\setupbodyfont [sans,36pt]
\starttext

\startMPcode

numeric r, g, b ;
def ran=
r := uniformdeviate 1 ;
g := uniformdeviate 1 ;
b := uniformdeviate 1 ;
enddef;

% Works as expected
for i=0 downto -3:
  ran;
  label(textext("\bold\colored[r=" & decimal(r) & ",g=" & decimal(g) &
		",b=" & decimal(b) & ",a=1, t=.2]{Test}"), (7cm,-1cm))
    rotatedaround ((7cm,-1cm),i*20);
endfor;

% Produces empty rectangles
for i=0 downto -3:
  ran;
  label(\sometxt{\bold{Test}}, (7cm,-4cm))
    rotatedaround ((7cm,-4cm),i*20)
    withcolor transparent("normal", .2, (r,g,b));
endfor;

\stopMPcode
\stoptext

Maybe there's a mistake in my code. It compiles without error but the
result is incorrect.

Marco

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\def\oklepaj#1{\left(#1\right)}
\def\t{\dot N(t)=
  A\oklepaj{\exp\oklepaj{-\frac{t-t_0}{τ_{\text{eksp.}}}}-\exp
    \oklepaj{-\frac{t-t_0}{τ_{\text{fast}}}}}+
  B\oklepaj{\exp\oklepaj{-\frac{t-t_0}{τ_{\text{eksp.}}}}-\exp
    \oklepaj{-\frac{t-t_0}{τ_{\text{slow}}}}}}
\def\T{Test}

\starttext
\doifmode{textext}{Mode: textext}
\doifmode{sometxt}{Mode: \letterbackslash sometxt}

\startmode [textext]
  \startMPcode
%   label(textext("$\t$\&"),origin); % doesn't work
    label(textext("$\t$\letterbackslash\&"),origin);
  \stopMPcode
\stopmode
\startmode [sometxt]
  \startMPcode
%   label(\sometxt{$\t$\&},origin); % doesn't work, either
    label(\sometxt{$\t$\letterbackslash\&},origin);
  \stopMPcode
\stopmode

\switchtobodyfont [sans, 36pt] \bf

\startmode [textext]
\startMPcode
for i=0 upto 100:
  label(textext("\colored [b=.7, a=1, t=.3]{\T}"),(i*1mm,0cm))
    rotatedaround ((i*1mm,0cm),i*2);
  label(textext("\colored [g=.7, a=1, t=.2]{\T}"),(i*1.1mm,0cm))
    rotatedaround ((i*1.1mm,0cm),i*2);
endfor;
\stopMPcode
\stopmode

\startmode [sometxt]
\startMPcode
for i=0 upto 100:
  label(\sometxt{\colored [b=.7, a=1, t=.3]{\T}},(i*1mm,0cm))
    rotatedaround ((i*1mm,0cm),i*2);
  label(\sometxt{\colored [g=.7, a=1, t=.2]{\T}},(i*1.1mm,0cm))
    rotatedaround ((i*1.1mm,0cm),i*2);
endfor;
\stopMPcode
\stopmode
\stoptext

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