Express boxes properties in tikz coordinates

Question

In my understanding, any LaTeX box displays such fundamental properties:

.. and anything is wrapped into a LaTeX box.

So, when I produce a tikz picture, it must be somehow wrapped into a box. Indeed, it seems to display such a height and a baseline when I use it. For instance, this code:

\documentclass{report}

\usepackage[english]{babel}

\usepackage{tikz}
  \tikzset{x=1pt, y=1pt, z=1pt}

\begin{document}

\newcommand{\mypicture}{\begin{tikzpicture}
        \node (a) at (0, 0) {\strut$a$};
        \node (b) at (30, 0) {\strut$b$};
        \draw[->] (a) .. controls (15, -20) and (30, -30) .. (b);
\end{tikzpicture}}

In my rather long, multilined text, I wish I could insert \mypicture{} just
as if it were something natural..

\end{document} 

produces:

.. now I think my point is getting clear. The above insertion does not seem natural at all since \mypicture box baseline does not match node (a) baseline. And if it would, vertical space between the two lines would probably be affected.

How to correct this without a dirty hand-tweak with \raisebox, \vspace etc.?

How to express all tikz pictures box properties in tikz coordinates?

Answer 1

In this case, you will have to tell TikZ where you want your baseline to be. Here you want it to be for example on your (a) node.

Here is a code to provide it :

\documentclass{report}

\usepackage[english]{babel}

\usepackage{tikz}
  \tikzset{x=1pt, y=1pt, z=1pt}

\begin{document}

\newcommand{\mypicture}{\begin{tikzpicture}[baseline=(a.base)]
        \node (a) at (0, 0) {\strut$a$};
        \node (b) at (30, 0) {\strut$b$};
        \draw[->] (a) .. controls (15, 20) and (30, 30) .. (b);
\end{tikzpicture}}

In my text, insert \mypicture{} just as if it were something natural..


\end{document}

And its result :

I hope it may help.

Answer 2

The general solution I needed was a combination of both baseline and the wonderful key use as bounding box: consider this :)

\documentclass[a4paper, 12pt]{report}

\usepackage{tikz}
    \tikzset{x=1pt, y=1pt, z=1pt}

\begin{document}

\def\myfig{\begin{tikzpicture}[baseline=(base)] % choose baseline
    % box dimensions
    \path[draw, use as bounding box] (0, 0) rectangle (10, 15);
    % set baseline
    \coordinate (base) at (0, 5);
    % actual content
    \path[fill=blue] (0, 0) % a random path
        ..  controls (10, 10)
                 and (10, -10) ..
                     (10, 20) -- cycle;
    % visualize baseline
    \draw (0, 5) -- (10, 5);
\end{tikzpicture}}

Now I can define \emph{every} frea\myfig ng property of my tikz box!

\end{document}

Phew!