[Tex/LaTex] Tikz & Beamer: Change color “after pause”

beamertikz-pgf

I have a tikz drawing, where I want to change the color of the edge in the second slide. Right now I'm doing that in the brute force way of drawing a new edge in red over the previous one.

Is there any way that reduces redundancy in the code, and doesn't force me to redefine the whole arrow over and over? Something like \alert<2> in the standard beamer environment?

In particular, if on the third slide, I wanted the edge black again, I'd have to draw it a third time, black — that sounds suboptimal.

Current approach:

\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{positioning}

\tikzstyle{block} = [rectangle, draw, 
text width=6em, text centered, rounded corners, minimum height=3em]

\begin{document}

    \begin{frame}

    \begin{tikzpicture}
    \node [block] (I2) {I2};
    \node [block] [left=5cm of I2] (I1) {I1};

\path[->] (I1) edge[shorten >=0.5cm, shorten <= 0.5 cm] node [right, near start, align=center] {$q=1$\\$p=2$} (I2);

    \visible<2>{    \path[->] (I1) edge[shorten >=0.5cm, shorten <= 0.5 cm, color=red] node [right, near start, color=red, align=center] {$q=1$\\$p=2$} (I2);}


    \end{tikzpicture}

    \end{frame}
\end{document}

Best Answer

In this simple case, you could get away with just changing the colour using \only<2>{\color{red}}

\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{positioning}

\tikzset{block/.style={rectangle, draw, text width=6em, text centered, rounded corners, minimum height=3em}}

\begin{document}

    \begin{frame}

    \begin{tikzpicture}
    \node [block] (I2) {I2};
    \node [block] [left=5cm of I2] (I1) {I1};

    {\only<2>{\color{red}}\path[->] (I1) edge[shorten >=0.5cm, shorten <= 0.5 cm] node [right, near start, align=center] {$q=1$\\$p=2$} (I2);}

    \end{tikzpicture}

    \end{frame}
\end{document}

The clean and more flexible way would be to use the overlay-beamer-styles library. Then you could use alt=<2>{red}{black} to specify different colours.

\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{positioning}

\usetikzlibrary{overlay-beamer-styles}

\tikzset{block/.style={rectangle, draw, text width=6em, text centered, rounded corners, minimum height=3em}}

\begin{document}

    \begin{frame}

    \begin{tikzpicture}
    \node [block] (I2) {I2};
    \node [block] [left=5cm of I2] (I1) {I1};

    \path[->,alt=<2>{red}{black}] (I1) edge[shorten >=0.5cm, shorten <= 0.5 cm] node [right, near start, align=center] {$q=1$\\$p=2$} (I2);

    \end{tikzpicture}

    \end{frame}
\end{document}

Related Solutions

[Tex/LaTex] Align edges with anchor other than center

I'm not sure to understand exactly the question . I understand that : you want an edge between two nodes but you want to draw the edge only between the intersections of the edges and the shapes of the nodes.

With intersections (the problem is to make a choice between the points) but in the second method I just fill the node's background.

\documentclass{scrartcl}
\usepackage{tikz}
\usetikzlibrary{positioning,intersections}
\begin{document}

\begin{tikzpicture}
  \node[name path= c1] (foo)  at (0,0)[circle] {$x$};
  \node[name path= c2] (bar) at (2,2)[circle] {$x+1$};
  \path[name path=line] (foo.south) -- (bar.center);
  \fill [name intersections={of=c1 and line, name=i, total=\t}]
 [red, opacity=0.5, every node/.style={left=.25cm, black, opacity=1}] 
 \foreach \s in {1,...,\t}{(i-\s) circle (2pt) node {}};
  \fill [name intersections={of=c2 and line, name=j, total=\t}]
 [red, opacity=0.5, every node/.style={left=.25cm, black, opacity=1}] 
 \foreach \s in {1,...,\t}{(j-\s) circle (2pt) node {}};   
  \draw[red] (i-1) -- (j-1);  
\end{tikzpicture} 
\begin{tikzpicture}
  \node[name path= c1] (foo)  at (0,0)[circle] {$x$};
  \node[name path= c2] (bar) at (2,2)[circle] {$x+1$};
  \path[name path=line] (foo.south) -- (bar.center);
  \path [name intersections={of=c1 and line, name=i, total=\t}] ;
  \path [name intersections={of=c2 and line, name=j, total=\t}];  
  \draw[red] (i-1) -- (j-1);  
\end{tikzpicture}
\begin{tikzpicture}
  \node (foo)  at (0,0)[circle] {\hphantom{$x$}};
  \node (bar) at (2,2)[circle] {\hphantom{$x+1$}};
  \draw[red] (foo.south) -- (bar.center);
  \node[circle,fill=white] at (foo.center){$x$} ;
  \node[circle,fill=white] at (bar.center){$x+1$} ; 
\end{tikzpicture}  
\end{document}

enter image description here

[Tex/LaTex] Connecting to a node towards a point other than the center

With the TikZ library intersections you can find the point on the node's rectangle quite easily.

We give the y node a path name: yborder.
We use one \path command to get the path from (x) to ($ (y.west)!0.5!(y) $) and name it xyline.

With name intersections={of=yborder and xyline} we get coordinates named intersections-1, intersections-2, …
In our case there's only one intersection, so intersection-1 will do.

(The PGF/TikZ manual shows how to deal with path intersections with more than one hit.)

Code

\documentclass[tikz,border=2pt]{standalone}
\usetikzlibrary{calc,intersections}
\begin{document}
\begin{tikzpicture}[every node/.style={draw,minimum size=1 cm}]
    \node                     (x) at (0cm,0cm) {x};
    \node [name path=yborder] (y) at (2cm,2cm) {y};
    \path [name path=xyline ] (x) -- ($ (y.west)!0.5!(y) $);
    \fill [red]               ($(y.west)!0.5!(y)$) circle[radius=1pt]; % Where's my point?
    \draw [name intersections={of=yborder and xyline},->]
                              (x) -- (intersection-1);
\end{tikzpicture}
\begin{tikzpicture}[every node/.style={circle,draw,minimum size=1 cm}]
    \node                     (x) at (0cm,0cm) {x};
    \node [name path=yborder] (y) at (2cm,2cm) {y};
    \path [name path=xyline ] (x) -- ($ (y.west)!0.5!(y) $);
    \fill [red]               ($(y.west)!0.5!(y)$) circle[radius=1pt]; % Where's my point?
    \draw [name intersections={of=yborder and xyline},->]
                              (x) -- (intersection-1);
\end{tikzpicture}
\end{document}

Output

rectangles circles