Estoy usando un tema Beamer personalizado simpleNeo, que una vez construí desde cero. Básicamente adapta los colores del tema estándar de Beamer, por lo que realmente no sucede nada especial. Los bloques con un título vacío todavía tienen un fondo azul más oscuro. ¿Por qué pasó esto? No puedo identificar la parte de mi tema que es responsable de esto.
\documentclass{beamer}
\usetheme{neo}
\begin{document}
\frame{
\begin{block}{}
Here is my text...
\end{block}
}
\end{document}
Respuesta1
Nueva solución
Con la versión v0.5 del tema interno de tcolorbox, puedes activar/desactivar el título vacío a voluntad:
\documentclass{beamer}
\usetheme{Berlin}
\useinnertheme[showtitle=false]{tcolorbox}
\begin{document}
\begin{frame}
\begin{block}{}
Here is my text...
\end{block}
\begin{block}{test}
Here is my text...
\end{block}
\end{frame}
\end{document}
Antigua solución
Imprime el título sólo si no está vacío:
\documentclass{beamer}
\usetheme{Berlin}
\usepackage{xstring}
\setbeamertemplate{block begin}
{
\par\vskip\medskipamount%
\IfStrEq{\insertblocktitle}{}{}{
\begin{beamercolorbox}[colsep*=.75ex]{block title}
\usebeamerfont*{block title}\insertblocktitle%
\end{beamercolorbox}%
}
{\parskip0pt\par}%
\ifbeamercolorempty[bg]{block title}
{}
{\ifbeamercolorempty[bg]{block body}{}{\nointerlineskip\vskip-0.5pt}}%
\usebeamerfont{block body}%
\begin{beamercolorbox}[colsep*=.75ex,vmode]{block body}%
\ifbeamercolorempty[bg]{block body}{\vskip-.25ex}{\vskip-.75ex}\vbox{}%
}
\begin{document}
\begin{frame}
\begin{block}{}
Here is my text...
\end{block}
\begin{block}{test}
Here is my text...
\end{block}
\end{frame}
\end{document}
Otra solución (parcial)
Como este problema no ocurre con los bloques redondeados, la idea es usarlos, pero cambiar su definición para que tengan radios de esquina de 0.
En el siguiente código arreglé la esquina superior izquierda (marcada con %%%% CHANGEDen el código), las otras esquinas aún deben arreglarse.
\documentclass{beamer}
\setbeamercolor{block title}{bg=blue}
\setbeamercolor{block body}{bg=blue!20}
\makeatletter
\renewcommand\beamerboxesrounded[2][]{%
\global\let\beamer@firstlineitemizeunskip=\relax%
\vbox\bgroup%
\setkeys{beamerboxes}{upper=block title,lower=block body,width=\textwidth,shadow=false}%
\setkeys{beamerboxes}{#1}%
{%
\usebeamercolor{\bmb@lower}%
\globalcolorstrue%
\colorlet{lower.bg}{bg}%
}%
{%
\usebeamercolor{\bmb@upper}%
\globalcolorstrue%
\colorlet{upper.bg}{bg}%
}%
%
% Typeset head
%
\vskip4bp
\setbox\bmb@box=\hbox{%
\begin{minipage}[b]{\bmb@width}%
\usebeamercolor[fg]{\bmb@upper}%
#2%
\end{minipage}}%
\ifdim\wd\bmb@box=0pt%
\setbox\bmb@box=\hbox{}%
\ht\bmb@box=1.5pt%
\bmb@prevheight=-4.5pt%
\else%
\wd\bmb@box=\bmb@width%
\bmb@temp=\dp\bmb@box%
\ifdim\bmb@temp<1.5pt%
\bmb@temp=1.5pt%
\fi%
\setbox\bmb@box=\hbox{\raise\bmb@temp\hbox{\box\bmb@box}}%
\dp\bmb@box=0pt%
\bmb@prevheight=\ht\bmb@box%
\fi%
\bmb@temp=\bmb@width%
\bmb@dima=\bmb@temp\advance\bmb@dima by2.2bp%
\bmb@dimb=\bmb@temp\advance\bmb@dimb by4bp%
\hbox{%
\begin{pgfpicture}{0bp}{+-\ht\bmb@box}{0bp}{+-\ht\bmb@box}
\ifdim\wd\bmb@box=0pt%
\color{lower.bg}%
\else%
\color{upper.bg}%
\fi%
\pgfpathqmoveto{-4.2bp}{3bp}
\pgfpathqcurveto{-2.2bp}{3bp}{-2.2bp}{3bp}{-2.2bp}{3bp} %%%% CHANGED
\pgfpathlineto{\pgfpoint{\bmb@temp}{3bp}}
\pgfpathcurveto%
{\pgfpoint{\bmb@dima}{3bp}}%
{\pgfpoint{\bmb@dimb}{1.2bp}}%
{\pgfpoint{\bmb@dimb}{-1bp}}%
\bmb@dima=-\ht\bmb@box%
\advance\bmb@dima by-2pt%
\pgfpathlineto{\pgfpoint{\bmb@dimb}{\bmb@dima}}
\pgfpathlineto{\pgfpoint{-4bp}{\bmb@dima}}
\pgfusepath{fill}
\end{pgfpicture}%
\copy\bmb@box%
}%
\nointerlineskip%
\vskip-1pt%
\ifdim\wd\bmb@box=0pt%
\else%
\hbox{%
\begin{pgfpicture}{0pt}{0pt}{\bmb@width}{60pt}
\bmb@dima=\bmb@width%
\advance\bmb@dima by8bp%
\pgfpathrectangle{\pgfpoint{-4bp}{-1bp}}{\pgfpoint{\bmb@dima}{8bp}}
\pgfusepath{clip}
{\pgftransformshift{\pgfpoint{-4bp}{0bp}}\pgftext[left,base]{\pgfuseshading{bmb@transition}}}%
\end{pgfpicture}%
}%
\nointerlineskip%
\vskip-0.5pt%
\fi%
\ifbmb@shadow%
\setbox\bmb@boxshadow=\hbox{\pgfuseshading{bmb@shadow}}%
\setbox\bmb@boxshadowball=\hbox{\pgfuseshading{bmb@shadowball}}%
\setbox\bmb@boxshadowballlarge=\hbox{\pgfuseshading{bmb@shadowballlarge}}%
\fi%
\setbox\bmb@colorbox=\hbox{{\pgfpicturetrue\pgfsetcolor{lower.bg}}}%
\setbox\bmb@box=\hbox\bgroup\begin{minipage}[b]{\bmb@width}%
\vskip2pt%
\usebeamercolor[fg]{\bmb@lower}%
\colorlet{beamerstructure}{upper.bg}%
\colorlet{structure}{upper.bg}%
%\color{.}%
}
\def\endbeamerboxesrounded{%
\end{minipage}\egroup%
\wd\bmb@box=\bmb@width%
\bmb@temp=\dp\bmb@box%
\advance\bmb@temp by.5pt%
\setbox\bmb@box=\hbox{\raise\bmb@temp\hbox{\box\bmb@box}}%
\dp\bmb@box=0pt%
\bmb@temp=\wd\bmb@box%
\bmb@dima=\bmb@temp\advance\bmb@dima by2.2bp%
\bmb@dimb=\bmb@temp\advance\bmb@dimb by4bp%
\hbox{%
\begin{pgfpicture}{0bp}{0bp}{0bp}{0bp}
\ifbmb@shadow%
{\pgftransformshift{\pgfpoint{4bp}{-3bp}}\pgftext{\copy\bmb@boxshadowball}}
\begin{pgfscope}
{%
\advance\bmb@temp by-1bp%
\pgfpathrectangle{\pgfpoint{\bmb@temp}{-7bp}}{\pgfpoint{9bp}{9bp}}%
\pgfusepath{clip}
}%
{\pgftransformshift{\pgfpoint{\bmb@temp}{1bp}}\pgftext{\box\bmb@boxshadowballlarge}}
\end{pgfscope}
\begin{pgfscope}
\advance\bmb@temp by-4bp%
\pgfpathrectangle{\pgfpoint{4bp}{-7bp}}{\pgfpoint{\bmb@temp}{5bp}}
\pgfusepath{clip}
{\pgftransformshift{\pgfpoint{4bp}{-7bp}}\pgftext[left,base]{\copy\bmb@boxshadow}}%
\end{pgfscope}
\begin{pgfscope}
\advance\bmb@temp by 4bp%
\bmb@dima=\ht\bmb@box%
\advance\bmb@dima by\bmb@prevheight%
\advance\bmb@dima by 4bp%
\pgfpathrectangle{\pgfpoint{\bmb@temp}{1bp}}{\pgfpoint{4bp}{\bmb@dima}}
\pgfusepath{clip}
\advance\bmb@dima by-4bp%
{\pgftransformshift{\pgfpoint{\bmb@temp}{\bmb@dima}}\pgftext{\box\bmb@boxshadowball}}
\advance\bmb@dima by-1bp%
\pgfpathrectangle{\pgfpoint{\bmb@temp}{1bp}}{\pgfpoint{4bp}{\bmb@dima}}
\pgfusepath{clip}
\advance\bmb@temp by4bp%
{\pgftransformshift{\pgfpoint{\bmb@temp}{-3bp}}%
\pgftransformrotate{90}%
\pgftext[left,base]{\box\bmb@boxshadow}}%
\end{pgfscope}
\fi%
\unhbox\bmb@colorbox%
\pgfpathqmoveto{-4bp}{1bp}
\pgfpathqcurveto{-4bp}{-1.2bp}{-2.2bp}{-3bp}{0bp}{-3bp}
\pgfpathlineto{\pgfpoint{\the\bmb@temp}{-3bp}}
\pgfpathcurveto%
{\pgfpoint{\the\bmb@dima}{-3bp}}%
{\pgfpoint{\the\bmb@dimb}{-1.2bp}}%
{\pgfpoint{\the\bmb@dimb}{1bp}}%
{
\bmb@dima=\ht\bmb@box%
\pgfpathlineto{\pgfpoint{\bmb@dimb}{\bmb@dima}}
\pgfpathlineto{\pgfpoint{-4bp}{\bmb@dima}}
\pgfusepath{fill}
}
\ifbmb@shadow%
{
\color{black!50!bg}
\pgfsetlinewidth{0pt}
\pgfpathmoveto{\pgfpoint{\bmb@dimb}{-.5bp}}
\bmb@dima=\ht\bmb@box%
\advance\bmb@dima by\bmb@prevheight%
\advance\bmb@dima by 1bp%
\pgfpathlineto{\pgfpoint{\bmb@dimb}{\bmb@dima}}
\pgfusepath{stroke}
\bmb@temp=\bmb@dima
\advance\bmb@dima by 1bp%
\color{black!31!bg}
\pgfpathmoveto{\pgfpoint{\bmb@dimb}{\bmb@temp}}
\pgfpathlineto{\pgfpoint{\bmb@dimb}{\bmb@dima}}
\pgfusepath{stroke}
\advance\bmb@dima by 1bp%
\advance\bmb@temp by 1bp%
\color{black!19!bg}
\pgfpathmoveto{\pgfpoint{\bmb@dimb}{\bmb@temp}}
\pgfpathlineto{\pgfpoint{\bmb@dimb}{\bmb@dima}}
\pgfusepath{stroke}
\advance\bmb@dima by 1bp%
\advance\bmb@temp by 1bp%
\color{black!6!bg}
\pgfpathmoveto{\pgfpoint{\bmb@dimb}{\bmb@temp}}
\pgfpathlineto{\pgfpoint{\bmb@dimb}{\bmb@dima}}
\pgfusepath{stroke}
\advance\bmb@dima by 1.5bp%
\advance\bmb@temp by 1bp%
\color{bg}
\pgfpathmoveto{\pgfpoint{\bmb@dimb}{\bmb@temp}}
\pgfpathlineto{\pgfpoint{\bmb@dimb}{\bmb@dima}}
\pgfusepath{stroke}
}
\fi
\end{pgfpicture}%
\box\bmb@box%
}%
\ifbmb@shadow%
\vskip4bp minus 2bp%
\else%
\vskip2bp%
\fi%
\egroup% of \vbox\bgroup
}
\makeatother
\setbeamertemplate{block begin}
{%
\par\vskip\medskipamount%
\begin{beamerboxesrounded}[upper=block title,lower=block body]%
{\raggedright\usebeamerfont*{block title}\insertblocktitle}%
\raggedright%
\usebeamerfont{block body}%
}
\setbeamertemplate{block end}
{\end{beamerboxesrounded}\vskip\smallskipamount}
\begin{document}
\begin{frame}
\begin{block}{}
content...
\end{block}
\end{frame}
\end{document}
