Beamer overlays: changing font between slides

Question

I am creating slides with overlays in Beamer, using TiKZ to create a figure consisting mainly of text nodes. The idea is that different parts of the figure are highlighted on each slide. Initially it all appears in a light gray (I'm using "seagull" colours with a white background), and on each slide a different part of the figure is shown in full colour.

I've achieved this by basically drawing the figure twice: once in light gray, and then drawing it again using a sequence of "onslide" commands. However, what I'd like is for text in a node to appear as bold face when it appears in colour. Here is an MWE:

\documentclass{beamer}

\usepackage{tikz}

\title{A test} 
\author{Me} 
\date{\today}

\begin{document} 

\begin{frame}   
  \maketitle 
\end{frame}

\begin{frame}{This is the test slide}

  \begin{tikzpicture}[remember picture,overlay,color=lightgray]
    \draw (current page.south west)++(1,1) coordinate (SW);
    \draw (SW)++(2,1) node {First bit of text};
    \draw (SW)++(4,3.5) node {Second bit of text};
    \draw (SW)++(6,6) node {Third and final text};
    \onslide<2>{\draw[color=blue] (SW)++(2,1) node {First bit of text};}
    \onslide<3>{\draw[color=blue] (SW)++(4,3.5) node {Second bit of text};}
    \onslide<4>{\draw[color=blue] (SW)++(6,6) node {Third and final  text};}     
  \end{tikzpicture}    
\end{frame}

\end{document}

Now there may well be an easier and more natural way of doing this; on the other hand it means I can position text wherever I want.

If I include a text = \bfseries in the second part of the above, then it seems to stick, and the lightgray text is also bold, which I don't want. So - any ideas on how text will appear in a color and bold, and then go back to lightgray and normal when it's not highlighted?

Answer 1

Is this what you want to achieve?

Draw the lightgray parts only on a specified number of slides using the \only<frame_number> command and afterwards use \onlide<2> (or another frame number` to draw the text in other font/color etc.

\documentclass{beamer}

\usepackage{tikz}

\title{A test} 
\author{Me} 
\date{\today}

\begin{document} 

\begin{frame}   
  \maketitle 
\end{frame}

\begin{frame}{This is the test slide}

  \begin{tikzpicture}[remember picture,overlay,color=red]
    \draw (current page.south west)++(1,1) coordinate (SW);
    \only<1,3-4>{\draw (SW)++(2,1) node {First bit of text};}
    \only<1-2,4>{\draw (SW)++(4,3.5) node {Second bit of text};}
    \only<1-3>  {\draw (SW)++(6,6) node {Third and final text}};
    \only<2>{\draw[color=blue] (SW)++(2,1) node {\textbf{First bit of text}};}
    \only<3>{\draw[color=blue] (SW)++(4,3.5) node {\textbf{Second bit of text}};}
    \only<4>{\draw[color=blue] (SW)++(6,6) node {\textbf{Third and final  text}};}     
  \end{tikzpicture}    
\end{frame}

\end{document}

I changed from lightgray to red just for the snapshot, because lightgray is hard to recognize in a screenshot.

Answer 2

Instead of drawing the content twice (which involves difficult to maintain code duplication), I suggest to just change the color and font attributes on the specific slides. In the following the onslide=<overlay spec>{key=value, key=value} TikZ style provides just that:

\documentclass{beamer}

\usepackage{tikz}

% TikZ stile to apply keys only on specific beamer overlays
% onslide=<overlay spec>{key=value, key=value, ...}
\tikzset{onslide/.code args={<#1>#2}{%
  \only<#1>{\pgfkeysalso{#2}}%
}}



\title{A test} 
\author{Me} 
\date{\today}

\begin{document} 

\begin{frame}   
  \maketitle 
\end{frame}

\begin{frame}{This is the test slide}

  \begin{tikzpicture}[remember picture,overlay,color=red]
    \draw (current page.south west)++(1,1) coordinate (SW);
    \draw[onslide=<2>{color=blue, font=\bfseries}] (SW)++(2,1) node {First bit of text};
    \draw[onslide=<3>{color=blue, font=\bfseries}] (SW)++(4,3.5) node {Second bit of text};
    \draw[onslide=<4>{color=blue, font=\bfseries}] (SW)++(6,6) node {Third and final text};
  \end{tikzpicture}    
\end{frame}

\end{document}

The code may further be improved by defining an own style for the highlighting, so that you can easily change that later or reuse it on other frames:

\tikzset{highlight/.style={color=blue, font=\bfseries}} 

\begin{tikzpicture}[remember picture,overlay,color=red]
  \draw (current page.south west)++(1,1) coordinate (SW);
  \draw[onslide=<2>{highlight}] (SW)++(2,1) node {First bit of text};
  \draw[onslide=<3>{highlight}] (SW)++(4,3.5) node {Second bit of text};
  \draw[onslide=<4>{highlight}] (SW)++(6,6) node {Third and final text};
\end{tikzpicture}

Further References:

• Highlighting specific parts of a TikZ drawing
• Mindmap tikzpicture in beamer (reveal step by step)
• Package aobs-tikz – TikZ styles for creating overlaid pictures in beamer

Answer 3

Better don't change font when highlighting, unless it is just a letter or single symbol. The widths and spacings change, which will led to labels wiggling around. To distracting. Better use color change only, say a (dark) gray vs red.