funny interference between \baselinestretch and TikZ

Question

The command \baselinestretch has a strange influence on Tikz Pictures, when it is not closed in a group (compare the two figures):

\documentclass[12pt]{article}
\usepackage{tikz}
\begin{document}
    \begin{tikzpicture}[scale = 2]
    \draw[very thick] (2,-0.2)+(30:1cm) arc (30:150:1cm);
    \end{tikzpicture}

    \renewcommand{\baselinestretch}{2}

    \begin{tikzpicture}[scale = 2]
    \draw[very thick] (2,-0.2)+(30:1cm) arc (30:150:1cm);
    \end{tikzpicture}
\end{document}

I know that i should enclose the \baselinestretch in a group, but i found this effect funny ! :) (and i needed quite a long time to track this bug inside my documents...)

Answer 1

Experimenting, it would appear that during the tikzpicture, \baselinestretch should be equal to whatever it was when the \begin{document} command was issued. Moreover, it should not be long (no matter what \baselinestretch was at the start) - this is an issue with the article.cls since that contains the line \renewcommand{\baselinestretch}{} which makes it \long, whereas latex.ltx simply contains \def\baselinestretch{1} so is not \long. The fact that article.cls makes it long is irrelevant by the time one gets into the document since \selectfont has implicitly made it not long again.

So until the bug is squished, here's a work-around. I've tested it with various combinations of setting \baselinestretch with and without \long and it seems to survive them all, but as I don't really understand what's going on here I can't be held responsible for any damage caused by this strange behaviour.

\documentclass[12pt]{article}
\usepackage{tikz}
\AtBeginDocument{\let\tikzbaselinestretch\baselinestretch}
\tikzset{every picture/.append style={
    execute at begin picture={%
      \edef\baselinestretch{\tikzbaselinestretch}%
    }
  }
}

\begin{document}
    \begin{tikzpicture}[scale = 2]
    \draw[very thick] (2,-0.2)+(30:1cm) arc (30:150:1cm);
    \end{tikzpicture}

    \renewcommand{\baselinestretch}{2}

    \begin{tikzpicture}[scale = 2]
    \draw[very thick] (2,-0.2)+(30:1cm) arc (30:150:1cm);
    \end{tikzpicture}
\end{document}

(Method incorporates suggestions from Jake, and experiments based on Altermundus' answer.)

---

Absolutely definitely a bug. But it's deep.

The bug is actually in \pgfmathsetlength. Quoting from the code:

Furthermore, the font is setup before the assignment is done, so that dimensions like 1em are evaluated correctly.

So within \pgfmathsetlength is a call to \pgfmath@selectfont. This is an alias of \selectfont (as we're using LaTeX) which calls \set@fontsize if \baselinestretch is not what it was the last time that \set@fontsize was called[1]. Then \set@fontsize executes \@defaultunits\@tempdimb#2pt\relax\@nnil. The upshot of is that if \baselinestretch has changed by some means other than a call to \set@fontsize then sometime in \pgfmathsetlength, \@tempdimb will get reassigned to something.

This, as Altermundus' hints at, causes problems for \pgfpatharc. Within that code is a call to \pgfpointpolar{\pgf@arc@angle}{\pgfutil@tempdima and \pgfutil@tempdimb}. In processing this, PGF calls \pgfmathsetlength but it does so before looking at the \pgfutil@tempdima and \pgfutil@tempdimb part. So before we look at it, \pgfutil@tempdimb gets reassigned and we've forgotten what it originally was.

So the problem is that \pgfutil@tempdimb (which is an alias for @tempdimb) gets set to a new value before it is used. Exactly how to fix this properly, I'll leave to the PGF team! A simple solution would be that after loading TikZ (or PGF) one puts:

\makeatletter
\newdimen\pgfutil@tempdimb
\makeatother

This separates the link between \pgfutil@tempdimb and \@tempdimb at the expense of using up a dimen register. An alternative would be to hack \set@fontsize so that the assignment to \@tempdimb occurred in a group. Taking a leaf out of TikZ/PGF's many smuggling routines, we could do:

\def\set@fontsize#1#2#3{%
  \bgroup
    \@defaultunits\@tempdimb#2pt\relax\@nnil
    \edef\@smuggle{{\edef\noexpand\f@size{\strip@pt\@tempdimb}}}%
  \expandafter\aftergroup\@smuggle
  \egroup
    \@defaultunits\@tempskipa#3pt\relax\@nnil
    \edef\f@baselineskip{\the\@tempskipa}%
    \edef\f@linespread{#1}%
    \let\baselinestretch\f@linespread
      \def\size@update{%
        \baselineskip\f@baselineskip\relax
        \baselineskip\f@linespread\baselineskip
        \normalbaselineskip\baselineskip
        \setbox\strutbox\hbox{%
          \vrule\@height.7\baselineskip
                \@depth.3\baselineskip
                \@width\z@}%
        \let\size@update\relax}%
  }

(I think that works without making any extra global assignments, but I'm no expert.)

[1] In slightly longer form, \set@fontsize saves the current value of \baselinestretch as a macro, \f@linespread (which is not \long), and then \lets \baselinestretch to this macro. So after calling \set@fontsize then \baselinestretch and \f@linespread are guaranteed to be the same. If someone interferes with \baselinestretch in the meantime, even just to \renewcommand\baselinestretch{whatever it currently is}, then this comparison will fail and \set@fontsize gets called again. In this case, \baselinestretch has been made \long because I didn't do \renewcommand*.

Answer 2

Perhaps the problem comes from

In latex.ltx there is

\def\set@fontsize#1#2#3{%
    \@defaultunits\@tempdimb#2pt\relax\@nnil
    \edef\f@size{\strip@pt\@tempdimb}%
    \@defaultunits\@tempskipa#3pt\relax\@nnil
    \edef\f@baselineskip{\the\@tempskipa}%

or in pgfutil-latex.def there is

\let\pgfutil@tempdima=\@tempdima
\let\pgfutil@tempdimb=\@tempdimb

and in pgfcorepathconstruct.code.tex

\def\pgf@arc{%
  {%
  \pgfutil@tempdima=\pgf@arc@radius@a pt%
  \pgfutil@tempdimb=\pgf@arc@radius@b pt%

Some Tex(perts) perhaps may confirm this hypothesis.

Update

The problem disappears if I redefine \def\pgf@arc{%

I replace \pgfutil@tempdimb by \mypgfutil@tempdimb

\documentclass[12pt]{article}  

\usepackage{tikz} 
\makeatletter
\newdimen\mypgfutil@tempdimb
\def\pgf@arc{%
  {%
  \pgfutil@tempdima=\pgf@arc@radius@a pt%
  \mypgfutil@tempdimb=\pgf@arc@radius@b pt%
  %
  \pgf@xa=\pgf@arc@local@angle@a\relax% 
  \pgf@xb=\pgf@arc@local@angle@b\relax%
  \advance\pgf@xb by-\pgf@xa\relax%
  \ifdim\pgf@xb<0pt\relax%
    \pgf@xb=-\pgf@xb\relax%
  \fi%
  \ifdim\pgf@xb=90.0pt%
    \def\pgfmathresult{0.55228475}%
  \else%
    \pgfmathparse{1.333333333*tan(.25*\pgf@sys@tonumber{\pgf@xb})}% many thanks to Ken Starks
  \fi%
  \pgfutil@tempdima=\pgfmathresult\pgfutil@tempdima%
  \mypgfutil@tempdimb=\pgfmathresult\mypgfutil@tempdimb%
  %.. controls +(\pgf@xa+90:\pgfutil@tempdima) and +(\pgf@xb-90:\pgfutil@tempdima) .. +(-(#1:#3)+(#2:#3))%
  % store first support vector in xa/ya:
  \pgf@xa=\pgf@arc@local@angle@a\relax%
  \ifdim\pgf@arc@local@angle@b>\pgf@arc@local@angle@a\relax%
    \advance\pgf@xa by 90pt\relax%
  \else%
    \advance\pgf@xa by -90pt\relax%
  \fi%
  \edef\pgf@arc@angle{\pgf@sys@tonumber{\pgf@xa}}%  
  \pgfpointtransformed{\pgfpointpolar{\pgf@arc@angle}{\pgfutil@tempdima and \mypgfutil@tempdimb}}%
  \advance\pgf@x by-\pgf@pt@x%
  \advance\pgf@y by-\pgf@pt@y%
  \pgf@xa=\pgf@path@lastx%
  \pgf@ya=\pgf@path@lasty%
  \advance\pgf@xa by \pgf@x%
  \advance\pgf@ya by \pgf@y%
  % store target in xb/yb:
  \pgfpointtransformed{\pgfpointpolar{\pgf@sys@tonumber{\pgf@arc@local@angle@a}}{\pgf@arc@radius@a pt and \pgf@arc@radius@b pt}}%
  \pgf@xb=\pgf@path@lastx%
  \pgf@yb=\pgf@path@lasty%
  \advance\pgf@xb by -\pgf@x%
  \advance\pgf@yb by -\pgf@y%
  \pgfpointtransformed{\pgfpointpolar{\pgf@sys@tonumber{\pgf@arc@local@angle@b}}{\pgf@arc@radius@a pt and \pgf@arc@radius@b pt}}%
  \advance\pgf@xb by \pgf@x%
  \advance\pgf@yb by \pgf@y%
  % store second support xc/yc:
  \ifdim\pgf@arc@local@angle@b>\pgf@arc@local@angle@a\relax%
    \advance\pgf@arc@local@angle@b by -90pt\relax%
  \else%
    \advance\pgf@arc@local@angle@b by 90pt\relax%
  \fi%
  \pgfpointtransformed{\pgfpointpolar{\pgf@sys@tonumber{\pgf@arc@local@angle@b}}{\pgfutil@tempdima and \mypgfutil@tempdimb}}%
  \advance\pgf@x by-\pgf@pt@x%
  \advance\pgf@y by-\pgf@pt@y%
  \pgf@xc=\pgf@xb\relax%
  \pgf@yc=\pgf@yb\relax%
  \advance \pgf@xc by \pgf@x\relax%
  \advance \pgf@yc by \pgf@y\relax%
  \pgfsyssoftpath@curveto{\the\pgf@xa}{\the\pgf@ya}{\the\pgf@xc}{\the\pgf@yc}{\the\pgf@xb}{\the\pgf@yb}%
  \global\pgf@path@lastx=\pgf@xb%
  \global\pgf@path@lasty=\pgf@yb%
  \pgf@protocolsizes{\pgf@xa}{\pgf@ya}%
  \pgf@protocolsizes{\pgf@xb}{\pgf@yb}%
  \pgf@protocolsizes{\pgf@xc}{\pgf@yc}%
  }%
}    


\begin{document}
    \begin{tikzpicture}[scale = 2]
    \draw[very thick] (2,-0.2)+(30:1cm) arc (30:150:1cm);
       \node[draw,align=right]{azerty\\qwerty} ;     
    \end{tikzpicture} 

    I recommend the setspace package. That package provides commands (singlespacing, 
onehalfspacing and doublespacing) and environments (singlespace, onehalfspace and 
oublespace) that allow to change the spacing within the document. You will find the documentation inside the setspace.sty file. (Stefan)


 \renewcommand{\baselinestretch}{2}  



      \begin{tikzpicture}[scale = 2]      
    \draw[very thick] (2,-0.2)+(30:1cm) arc (30:150:1cm);
    \node[draw,align=right]{azerty\\qwerty} ;
    \end{tikzpicture}  

     I recommend the setspace package. That package provides commands (singlespacing,
 onehalfspacing and doublespacing) and environments (singlespace, onehalfspace and 
doublespace) that allow to change the spacing within the document. You will find the 
documentation inside the setspace.sty file.  (Stefan) 

\end{document}

Solution (workaround)

First there is no problem if you use \renewcommand{\baselinestretch}{2} in the preamble. Logically I've not tested but perhaps you can use \renewcommand{\baselinestretch}{2} in a group if you want to change locally.

Then you can remark that inside the nodes the baselineskip is also changed.

Finally a good idea is to use the setspace package like Stefan writes on his blog !

\documentclass[12pt]{article}  
\usepackage{setspace}
\usepackage{tikz} 
%\renewcommand{\baselinestretch}{2} 
\begin{document}
    \begin{tikzpicture}[scale = 2]
    \draw[very thick] (2,-0.2)+(30:1cm) arc (30:150:1cm);
       \node[draw,align=right]{azerty\\qwerty} ;     
    \end{tikzpicture} 

I recommend the setspace package. That package provides commands (singlespacing, 

onehalfspacing and doublespacing) and environments (singlespace, onehalfspace and doublespace) that allow to change the spacing within the document. You will find the documentation inside the setspace.sty file. (Stefan)

  \doublespacing

I recommend the setspace package. That package provides commands (singlespacing, 

onehalfspacing and doublespacing) and environments (singlespace, onehalfspace and doublespace) that allow to change the spacing within the document. You will find the documentation inside the setspace.sty file. (Stefan)

      \begin{tikzpicture}[scale = 2] 
    \draw[very thick] (2,-0.2)+(30:1cm) arc (30:150:1cm);
    \node[draw,align=right]{azerty\\qwerty} ;
    \end{tikzpicture}  
\end{document}