[Tex/LaTex] Vertical space inserted before itemize environment at the top of a minipage in beamer

beameritemize

See bottom for an updated MWE and more analysis after touhami's feedback.

The problem I'm seeing is that an itemize environment at the top of a beamer column (columns with [t] alignment) introduces a blank line. I was trying to align the lines of itemize in a column with the text lines in the other column, so I changed the relevant parameters (\topsep and \itemsep) modifiying some code from the beamer class. However, the issue is not caused by such modification; indeed, if I comment the lines in the preamble (see the MWE), the effect is still there. I keep them in the minimal example so that it is evident that the inserted vertical space corresponds to exactly one line. I can fix the vertical space by inserting \vspace{-\baselineskip} at the beginning of the column in every slide with this problem, but I would like to know if there is a way to fix it globally in a presentation.

Some comments:

If the columns aligment is changed to [T], the vertical space is reduced, but the lines in the two columns are no more aligned.
This only happens if the itemize environment is at the top of the column: if some text is added before the environment, no vertical space is inserted and the lines are aligned.
The order of the columns does not matter: the problem also appears if the itemize environment is in the first one.

A minimal working example:

\documentclass{beamer}

%%% These lines are a modified version of the code from the beamer 
%%% class (file beamerbaselocalstructure.sty). If they are commented
%%% out, the effect is still present\makeatletter
\makeatletter
\def\@listi{
  \leftmargin\leftmargini
  \topsep  0pt
  \parsep  0pt
  \itemsep 0pt
}
\let\@listI\@listi
\makeatother

\begin{document}
\begin{frame}
  % If this is changed to [T] the lines are not aligned
  \begin{columns}[t]
    \column{5cm}
    This is some text only to show the alignment (or the lack of it)
    between this column and the following one which starts with an
    itemize environment.
    \column{5cm}
    %%% This vertical space corresponds to normal a text line, but
    %%% only happens if the itemize environment is at the beginning of
    %%% the column: indeed if we uncomment the next line, the items do
    %%% not move.
    % Something
    %%% This is a manual workaround, but I'd prefer a global fix
    % \vspace{-\baselineskip}
    \begin{itemize}
    \item First
    \item Second
    \item Third
    \item Fourth
    \end{itemize}
  \end{columns}
\end{frame}
\end{document}

(Edit) In the case of T alignment, the problem can be solved by also setting \partopsep to zero, as suggested by Ignasi in his comment, but this does not work with t alignment. Then, looking at the difference between the two alignment options at the beginning of touhami's answer, I cannot see why the extra vertical space is inserted. It seem that it can be suppressed by \notinterlineskip, but why is it inserted in the first place?

(Update)
The problem is present also when the itemize environment is at the top of a minipage (on which beamer columns are based). Therefore another MWE that shows the issue is the following:

\documentclass{beamer}

\makeatletter
\def\@listi{
  \leftmargin\leftmargini
  \topsep  0pt
  \parsep  0pt
  \itemsep 0pt
}
\let\@listI\@listi
\makeatother

\begin{document}
\begin{frame}
  \begin{minipage}[t]{3cm}
    This is a minipage with some text to show the issue.
  \end{minipage}
  \begin{minipage}[t]{5cm}
    Text in the top line.
    \begin{itemize}
    \item An item.
    \item A second item.
    \end{itemize}
  \end{minipage}
  \vspace{3ex}

  \begin{minipage}[t]{3cm}
    This is a minipage with some text to show the issue.
  \end{minipage}
  \begin{minipage}[t]{5cm}
    \begin{itemize}
    \item Item in the top line.
    \item A second item.
    \end{itemize}
  \end{minipage}
\end{frame}
\end{document}

As you can see, if there is a text line at the top of a minipage on the right (first case), the lines of the itemize environment are properly aligned with those in the left minipage. On the other hand, if the itemize environment is at the top of the minipage some vertical space is inserted. After some further investigations I came to the following conclusions:

The inserted vertical space is smaller that that in the first MWE, but it becomes the same if I add \leavevmode before \begin{itemize} (as in the definition of beamer column environment).
The issue is caused by the beamer class: if documentclass is changed to article (and the frame environment is removed) no vertical space is inserted.
However, the issue does not seem to be related to the redefinition of itemize environment by the beamer class. If I comment the code in lines 240-265 of beamerbaselocalstructure.sty in which \itemize and \enditemize are redefined, the beamer item markers disappear but the vertical space stays the same.

Best Answer

Update (just a comment) as one can see from this code, the problem is not related to \column command (minipage is behind). It seems that the source of problem is \itemize (or deeper \list).

\documentclass{beamer}

\begin{document}
\begin{frame}
\begin{minipage}[t]{.48\textwidth}
These lines are a modified version of the code from the beamer 
 class (file beamerbaselocalstructure.sty). If they are commented
 out, the effect is still present
\end{minipage}
\hfill
\begin{minipage}[t]{.48\textwidth}%\vskip-1ex
%These lines are a modified versio
    \begin{itemize}
    \item First
    \item Second
    \item Third
    \item Fourth
    \end{itemize}
\end{minipage}
\end{frame}
\end{document}

Here is a solution. By default

\define@key{beamer@col}{t}[true]{\def\beamer@colmode{t}\def\beamer@colalign{t}\def\beamer@colheadskip{}}
\define@key{beamer@col}{T}[true]{\def\beamer@colmode{T}\def\beamer@colalign{t}\def\beamer@colheadskip{\vskip-1ex\nointerlineskip}}

so one can try

\define@key{beamer@col}{t}[true]{\def\beamer@colmode{t}\def\beamer@colalign{t}\def\beamer@colheadskip{\vskip-1ex\nointerlineskip}}

MWE

\documentclass{beamer}

%%% These lines are a modified version of the code from the beamer 
%%% class (file beamerbaselocalstructure.sty). If they are commented
%%% out, the effect is still present\makeatletter
\makeatletter
\define@key{beamer@col}{t}[true]{\def\beamer@colmode{t}\def\beamer@colalign{t}\def\beamer@colheadskip{\vskip-1ex\nointerlineskip}}
\def\@listi{
  \leftmargin\leftmargini
  \topsep  0pt
  \parsep  0pt
  \itemsep 0pt
}
\let\@listI\@listi
\makeatother

\begin{document}
\begin{frame}
  % If this is changed to [T] the lines are not aligned
  \begin{columns}[t]
    \column{5cm}
    This is some text only to show the alignment (or the lack of it)
    between this column and the following one which starts with an
    itemize environment.
    \column{5cm}
    % This vertical space corresponds to normal a text line, but
    %%% only happens if the itemize environment is at the beginning of
    %%% the column: indeed if we uncomment the next line, the items do
    %%% not move.
    % Something
    %%% This is a manual workaround, but I'd prefer a global fix
    % \vspace{-\baselineskip}
    \begin{itemize}
    \item First
    \item Second
    \item Third
    \item Fourth
    \end{itemize}
  \end{columns}
\end{frame}
\end{document}

How to fix the problem

According to the above explanation of the behavior of \vtop, the solution will be to make sure that the very first item inside the \vtop box is the \hbox containing the first line of text. Thus, we have to avoid any \kerns, color changes etc. at the top of the minipage. In the code below I roughly explain the main ideas. The code is tested with various combinations of overlay commands and manual color changes.

\documentclass{beamer}
\makeatletter
\def\beamer@callorigitem{%
  \@ifnextchar[
    \beamer@@callorigitem
    {\beamer@origitem
     \if@minipage\else
       \kern0pt  % don't put the \kern at the top of a \minipage
     \fi
     \ignorespaces
    }%
  }
\newcommand*\if@minipage@and@vmode[2]{%
  \let\mini@vmode 0%
  \if@minipage\ifvmode
    \let\mini@vmode 1%
  \fi\fi
  \if\mini@vmode 1 #1\else #2\fi
}
% Redefine \beamerorig@set@color, \pgfsys@begininvisible and \pgfsys@endinvisible
% such that they don't act at the top of a \minipage;
% instead save the corresponding commands in \set@minipage@color ...
\def\set@minipage@color{}%
\let\save@beamerorig@set@color\beamerorig@set@color
\def\beamerorig@set@color{%
  \if@minipage@and@vmode{%
    \begingroup
    \def\reset@color{\relax}%
    \xdef\addto@minipage@color{\save@beamerorig@set@color}%
    \endgroup
    \expandafter\g@addto@macro\expandafter\set@minipage@color
                              \expandafter{\addto@minipage@color}%
    \aftergroup\reset@color
  }{%
    \save@beamerorig@set@color
  }%
}
\let\save@pgfsys@begininvisible\pgfsys@begininvisible
\let\save@pgfsys@endinvisible\pgfsys@endinvisible
\def\pgfsys@begininvisible{%
  \if@minipage@and@vmode
    {\g@addto@macro\set@minipage@color{\save@pgfsys@begininvisible}}
    {\save@pgfsys@begininvisible}%
}
\def\pgfsys@endinvisible{%
  \if@minipage@and@vmode
    {\g@addto@macro\set@minipage@color{\save@pgfsys@endinvisible}}
    {\save@pgfsys@endinvisible}%
}
% ... and execute them at the beginning of the first paragraph of the minipage
% (where \everypar issues \@minipagefalse).
\let\save@minipagefalse\@minipagefalse
\def\@minipagefalse{%
  \set@minipage@color
  \gdef\set@minipage@color{}%
  \save@minipagefalse
}
\makeatother
\begin{document}
\begin{frame}
\begin{minipage}[t]{1.6cm}
Questions:
\end{minipage}\nobreak
\begin{minipage}[t]{9cm}
\begin{itemize}
\item 1st question;
\item 2nd question.
\end{itemize}
\end{minipage}
\end{frame}
\end{document}

If one compiles this with

\tracingoutput=2
\showboxbreadth=\maxdimen \showboxdepth=\maxdimen

in the preamble, then in the log file one finds the lines

.....\vbox(7.43904+18.72917)x256.0748
......\hbox(7.43904+2.12917)x234.17474, glue set 87.88736fil, shifted 21.90005

This tells that the second minipage is a \vbox with a height of 7.43904pt and a depth of 18.72917, and that the first item inside the \vbox is an \hbox. Without my redefinitions of \beamer@callorigitem, \beamerorig@set@color, \pgfsys@begininvisible and \pgfsys@endinvisible, one will find

.....\vbox(0.0+26.16821)x256.0748
......\pdfcolorstack 0 push {0 g 0 G}
......\kern 0.0

in the log file instead. This means that the second minipage is a \vbox with height 0pt (and one sees the color change and the \kern responsible for this!).

How to "officially" fix it

The problem isn't really beamer specific, except for the \kern0pt in \beamer@callorigitem from beamerbaseoverlay.sty. One gets the same misalignment with the article document class if one uses, e.g., \color{red} at the top of the minipage. The changes to \beamerorig@set@color (which is \let to \set@color by beamer) and to \@minipagefalse would best fit into the xcolor package; the changes to \pgfsys@begininvisible and \pgfsys@endinvisible should go to pgfsys.code.tex.

[Tex/LaTex] How to modify itemize vertical spacing within blocks in beamer

There are two things going on in this situation. For those who know about LaTeX's list parameters, there is a \topsep being added before the itemize list. The other is that this item is starting in vertical mode, so a \partopsep is also being added.

We thus need to do two things in this situation: (1) set \topsep to zero for the list, via a redefinition \@listi, and (2) clear \partopsep.

The best way to do this is to add this to block begin template. Here is an example, based on the essentials of your code.

\documentclass[10pt]{beamer}
\usepackage{lmodern}
\usepackage[T1]{fontenc}

\usetheme{default}
\usecolortheme{crane}

\setbeamertemplate{itemize items}[square]

\setbeamercolor{item}{fg=black}
\setbeamercolor{frametitle}{fg=black}
\setbeamercolor{block title}{fg=black}
\setbeamercolor{title}{fg=black}
\setbeamercolor{block body}{bg=white}

\makeatletter
\addtobeamertemplate{block begin}{
\def\@listi{\leftmargin\leftmargini
              \topsep    0pt
              \parsep    0pt
              \itemsep   3pt plus 2pt minus 3pt}
\partopsep 0pt
}
\makeatother

\begin{document}


\begin{frame}
  \frametitle{text vs. item blocks}
  \begin{columns}[t]
    \begin{column}{0.42\textwidth}
      \begin{block}{text block}
        block block block block block\vadjust{\hrule}
        block block block block block 
        block block block block block 
        block block block block block 
      \end{block}
    \end{column}
    \begin{column}{0.48\textwidth}
      \begin{block}{item block}
        \begin{itemize}
        \item item\vadjust{\hrule}
        \item item
        \item item
        \end{itemize}
      \end{block}
    \end{column}
  \end{columns}
\end{frame}

\end{document}

Sample output

I have placed the blocks side-by-side and added the \vadjust{\hrule} for illustration purposes. The values for \@listi are based on beamers defaults which are

\def\@listi{\leftmargin\leftmargini
            \topsep 3\p@ \@plus2\p@ \@minus2.5\p@
            \parsep 0\p@
            \itemsep3\p@ \@plus2\p@ \@minus3\p@}

\partopsep has default value

2.0pt plus 1.0pt minus 1.0pt

If you want the individual lines to match up, then you should also put \itemsep equal to 0pt in the above code.

Beaware that if the titles of the two blocks have different heights/depths then theh body will move accordingly and you will loose your alignment again. You can cover yourself a little by adding an appropriate strut to your block titles.

Note that the above code also kills \topsep for subsquent uses of itemize within the same block. If this is a problem, you might try to just adjust \partopsep to cancel out \topsep and ensure that your subsequent lists in the block do not start in vertical mode.

Best Answer

Related Solutions

[Tex/LaTex] In beamer class, how to remove the additional vertical space before an itemize environment

How to fix the problem

How to "officially" fix it

[Tex/LaTex] How to modify itemize vertical spacing within blocks in beamer

Related Question