TIKZ/PGF: How to override the opacity of the text inside a node?

Question

I am trying to incrementally reveal one node at a time in a figure while preserving the text alignment across two nodes.

Here is an example:

\documentclass[presentation]{beamer}
\usepackage{tikz}
\usepackage{transparent}
\usepackage{xcolor}

\tikzset{
  invisible/.style={opacity=0},
  visible on/.style={alt={#1{}{invisible}}},
  alt/.code args={<#1>#2#3}{%
    \alt<#1>{\pgfkeysalso{#2}}{\pgfkeysalso{#3}} % \pgfkeysalso doesn't change the path
  },
}
\newcommand{\x}{{\color{blue}\ensuremath{x}}}

\begin{document}
\begin{frame}
\begin{figure}
    \centering
    \begin{tikzpicture}
      \begin{scope}
        \node[visible on=<1>] (b00) at (0, 0) {
            {\transparent{0}$3 \cdot ($}
            $f(\x)$
            {\transparent{0}$) + 5$}
            {$=$}
            {\transparent{0}$3 \cdot ($}
            $g(\x) * h(\x)$
            {\transparent{0}$) + 5$}
        };
        \node[visible on=<2>] (b00) at (0, 0) {
            {\transparent{0.5}$3 \cdot ($}
            $f(\x)$
            {\transparent{0.5}$) + 5$}
            {$=$}
            {\transparent{0.5}$3 \cdot ($}
            $g(\x) * h(\x)$
            {\transparent{0.5}$) + 5$}
        };
      \end{scope}
    \end{tikzpicture}
\end{figure}
\end{frame}
\end{document}

I am trying to get: f(x) = g(x) ∗ h(x) in the first slide and 3·(f(x)) + 5 = 3.(g(x)∗h(x)) + 5 in the second slide while preserving the alignment of f(x) = g(x) ∗ h(x) across both slides.

Is there a clean way to do this in TIKZ/PGF?

Answer 1

You can let beamer do the uncovering for you:

\documentclass[presentation]{beamer}
\usepackage{tikz}
\setbeamercovered{transparent}

\newcommand{\x}{{\color{blue}\ensuremath{x}}}

\setbeamercovered{still covered={\opaqueness<1>{30}\opaqueness<2->{0}}}

\begin{document}
\begin{frame}<-2>
\begin{figure}
    \begin{tikzpicture}
      \begin{scope}
        \node (b00) at (0, 0) {
          $
            \uncover<3->{3 \cdot (}
            f(\x)
            \uncover<3->{) + 5}
            =
            \uncover<3->{3 \cdot (}
            g(\x) * h(\x)
            \uncover<3->{) + 5}
          $
        };
      \end{scope}
    \end{tikzpicture}
\end{figure}
\end{frame}
\end{document}

Answer 2

Welcome to TeX.SX! You can simply color parts of the math. There is no need to seperate it that much. Use begingroup and \endgroup (like suggested in this answer in order to keep the spacing correct even for binary operators (which is not a problem in your case, anyways).

I would suggest that you use the library overlay-beamer-styles for TikZ instead of providing your own visible on style. In the following code I added a slide without color to ehow that the spacing is correct.

\documentclass[presentation]{beamer}
\usepackage{tikz}
\usetikzlibrary{overlay-beamer-styles}

%\newcommand{\x}{{\color{blue}\ensuremath{x}}}

\newcommand{\makeblue}[1]{\begingroup\color{blue}\ensuremath{#1}\endgroup}
\newcommand{\maketransparent}[2][0]{\begingroup\color{black!#1}\ensuremath{#2}\endgroup}

\begin{document}
\begin{frame}
\begin{figure}
    \centering
    \begin{tikzpicture}
      \begin{scope}
        \node[visible on=<1>] (b00) at (0, 0) {
            $\maketransparent{3 \cdot (}
            f(\makeblue{x})
            \maketransparent{) + 5}
            =
            \maketransparent{3 \cdot (}
            g(\makeblue{x}) * h(\makeblue{x})
            \maketransparent{) + 5}$
        };
        \node[visible on=<2>] (b00) at (0, 0) {
            $\maketransparent[50]{3 \cdot (}
            f(\makeblue{x})
            \maketransparent[50]{) + 5}
            =
            \maketransparent[50]{3 \cdot (}
            g(\makeblue{x}) * h(\makeblue{x})
            \maketransparent[50]{) + 5}$
        };
        \node[visible on=<3>] (b00) at (0, 0) {
            $3 \cdot (f(x)) + 5 = 3 \cdot (g(x) * h(x)) + 5$
        };
      \end{scope}
    \end{tikzpicture}
\end{figure}
\end{frame}
\end{document}

---

A more flexible command could be:

\NewDocumentCommand{\maketransparent}{ O{0} O{black} m }{\begingroup\color{#2!#1}\ensuremath{#3}\endgroup}

It takes three arguments, two of which are optional and can be used to set the color and the opacity. The third argument takes the stuff that should be colored. A few examples:

\maketransparent{a}           % print an invisible a

\maketransparent[25]{a}       % print an a with 25 % opacity

\maketransparent[25][red]{a}  % print a red a with 25 % opacity