How to conditionally load `tikz` and draw a TikZ diagram when `preview` is not loaded

Question

How can I conditionally load tikz and draw a TikZ diagram only when preview is not loaded, i.e., AUCTeX is not generating images for other things (e.g., mathematical formulas)?

MWE:

 \documentclass{amsart}
 \usepackage{tikz} %*
 \begin{document}
 \[ a^2 + b^2 = c^2 \]
 \begin{figure}[htbp]
 \begin{tikzpicture} %*
 \draw (0, 0) -- (1, 1); %*
 \end{tikzpicture} %*
 \end{figure}
 \end{document}

I'd like to exclude the lines with %* when AUCTeX generates images.

Addendum: AUCTeX loads preview by using \AtBeginDocument, like this:

 latex -ini -interaction=nonstopmode "&latex" prv_hoge.ini "\nonstopmode\nofiles\PassOptionsToPackage{active,tightpage,auctex}{preview}\AtBeginDocument{\ifx\ifPreview\undefined\RequirePackage[displaymath,floats,graphics,textmath,sections,footnotes]{preview}[2004/11/05]\fi}" "\input" mwe.tex

So branching by using \@ifpackageloaded in the preamble doesn't quite work. What's an alternative?

Answer 1

You can use \@ifpackageloaded{preview}{}{}.

References:

• What do \makeatletter and \makeatother do?

Code:

\documentclass{amsart}
\makeatletter
     @ifpackageloaded{preview}{%
     }{%
         \usepackage{tikz}%
     }%
 \makeatother
\begin{document}
 [ a^2 + b^2 = c^2 ]
 \begin{figure}[htbp]
 \begin{tikzpicture} %*
 \draw (0, 0) -- (1, 1); %*
 \end{tikzpicture} %*
 \end{figure}
 \end{document}