Box around several but different items in an itemize environment

Question

I am trying to highlight, at the end of my slide, several items in a list with a box in something similar as in the method shown in Box around a few items in an itemize environment.

The difference is that instead of only one box I want to use two boxes as I compare the elements with another block.

I used the following code:

\documentclass[pdf,10pt,xcolor=table]{beamer}
    \usepackage{xparse}%  For \NewDocumentCommand
    \usepackage{calc}%    For the \widthof macro
    \usepackage{tikz}
    \usetikzlibrary{calc}
    \newcommand{\tikzmark}[1]{\tikz[overlay,remember picture] \node (#1) {};}
    %
    \makeatletter
    %
    \NewDocumentCommand{\DrawBox}{s O{}}{%
        \tikz[overlay,remember picture]{
        \IfBooleanTF{#1}{%
            \coordinate (RightPoint) at ($(left |- right)+(\linewidth-\labelsep-\labelwidth,0.0)$);
            }{%
            \coordinate (RightPoint) at (right.east);
            }%
        \draw[red,#2]
            ($(left)+(-0.2em,0.9em)$) rectangle
            ($(RightPoint)+(0.2em,-0.3em)$);}
        }

    \NewDocumentCommand{\DrawBoxWide}{s O{}}{%
        \tikz[overlay,remember picture]{
        \IfBooleanTF{#1}{%
             \coordinate (RightPoint) at ($(left |- right)+(\linewidth-\labelsep-\labelwidth,0.0)$);
             }{%
             \coordinate (RightPoint) at (right.east);
             }%
         \draw[red,#2]
             ($(left)+(-\labelwidth,0.9em)$) rectangle
             ($(RightPoint)+(0.2em,-0.3em)$);}
         }
    %
    \makeatother
    %
    \begin{document}
        \begin{frame}
            \begin{block}{\centering Unsteady models}
                \begin{itemize}\setbeamertemplate{itemize  item}[triangle]\small
                    \item\tikzmark{left}\textbf{Aerodynamics}
                        \begin{itemize}\small
                            \item[+] \textbf<3->{Accuracy}
                            \item[+] \textbf<3->{Flow physics}\tikzmark{right}
                        \end{itemize}
                    \item\tikzmark{left}\textbf{Structure}
                        \begin{itemize}\small
                    \item[+] \textbf<3->{Full wing flexibility}\tikzmark{right}
                        \end{itemize}
                    \item \textbf{Implementation}
                        \begin{itemize}\small
                            \item[-] Complex formulation
                            \item[-] High computational load
                        \end{itemize}
                \end{itemize}
            \end{block}
            \only<3->{\DrawBoxWide[thick, green, fill=green, fill opacity=.25]}
        \end{frame}
    \end{document}

Additionally, I am not completely satisfied with the box solution as I am using the list in a block which has a background color and thus diminishes the effect of the surrounding box.

I saw that the tikz style can also highlight parts of a list, as in Beamer overlay box around text - the correct way? and Highlighting in beamer using TikZ nodes, but I didn't see an example around several items without any blank between the items.

Furthermore in the example given the item marker is included by \DrawBoxWide*{} which is not the case for me.

Do you have a solution, for these issues?

Answer 1

Perhaps this is what you need?

\documentclass[10pt,xcolor=table]{beamer}
\usetheme{Madrid}
\usepackage{tikz}
\usepackage{twoopt}
\usetikzlibrary{calc}

\makeatletter
\tikzset{%
  remember picture with id/.style={%
    remember picture,
    overlay,
    save picture id=#1,
  },
  save picture id/.code={%
    \edef\pgf@temp{#1}%
    \immediate\write\pgfutil@auxout{%
      \noexpand\savepointas{\pgf@temp}{\pgfpictureid}}%
  },
  if picture id/.code args={#1#2#3}{%
    \@ifundefined{save@pt@#1}{%
      \pgfkeysalso{#3}%
    }{
      \pgfkeysalso{#2}%
    }
  }
}

\def\savepointas#1#2{%
  \expandafter\gdef\csname save@pt@#1\endcsname{#2}%
}

\def\tmk@labeldef#1,#2\@nil{%
  \def\tmk@label{#1}%
  \def\tmk@def{#2}%
}

\tikzdeclarecoordinatesystem{pic}{%
  \pgfutil@in@,{#1}%
  \ifpgfutil@in@%
    \tmk@labeldef#1\@nil
  \else
    \tmk@labeldef#1,(0pt,0pt)\@nil
  \fi
  \@ifundefined{save@pt@\tmk@label}{%
    \tikz@scan@one@point\pgfutil@firstofone\tmk@def
  }{%
  \pgfsys@getposition{\csname save@pt@\tmk@label\endcsname}\save@orig@pic%
  \pgfsys@getposition{\pgfpictureid}\save@this@pic%
  \pgf@process{\pgfpointorigin\save@this@pic}%
  \pgf@xa=\pgf@x
  \pgf@ya=\pgf@y
  \pgf@process{\pgfpointorigin\save@orig@pic}%
  \advance\pgf@x by -\pgf@xa
  \advance\pgf@y by -\pgf@ya
  }%
}
\makeatother
\newcommand\tikzmark[2][]{%
\tikz[remember picture with id=#2] #1;}

\newcommandtwoopt\DrawBox[4][][-\labelwidth+\labelsep]{%
\begin{tikzpicture}[overlay,remember picture]
\draw[red,#1]
            ($(pic cs:#3)+(-0.2em+#2,0.9em)$) rectangle
            ($(pic cs:#4)+(0.2em,-0.3em)$);
\end{tikzpicture}}

\begin{document}

\begin{frame}
\begin{block}{\centering Unsteady models}
\only<3->{\DrawBox[thick, green!50!black, fill=green!80!black]{lefta}{righta}}
\only<4->{\DrawBox[thick, green!50!black, fill=green!80!black]{leftb}{rightb}}
\begin{itemize}\setbeamertemplate{itemize  item}[triangle]\small
\item\tikzmark{lefta}\textbf{Aerodynamics}
  \begin{itemize}\small
  \item[+] \textbf<3->{Accuracy}
  \item[+] \textbf<3->{Flow physics}\tikzmark{righta}
  \end{itemize}
\item\tikzmark{leftb}\textbf{Structure}
  \begin{itemize}\small
  \item[+] \textbf<3->{Full wing flexibility}\tikzmark{rightb}
  \end{itemize}
\item \textbf{Implementation}
  \begin{itemize}\small
  \item[-] Complex formulation
  \item[-] High computational load
  \end{itemize}
\end{itemize}
\end{block}
\end{frame}

\end{document}

The new \DrawBox command has two optional arguments: the first one, to pass options to the \draw command internally used for the frame, and the second one, to control the horizontal offset to the left (default value=-\labelwidth+\labelsep); the two mandatory arguments are for the marks which should be set in the proper locations.

I used the improved \tikzmark defined by Andrew Stacey in his answer to tikzmark to have different behaviour if first run (and mark locations not yet available). This, in particular, places the box behind the text, so no need to use opacity (unless its effect is really required).