Estou usando um tema simples e personalizado do BeamerNeo, que uma vez construí do zero. Basicamente, ele adapta as cores do tema padrão do Beamer, então nada de sofisticado realmente acontece. Os blocos com título vazio ainda apresentam fundo azul mais escuro. Por que isso acontece? Não consigo identificar a parte do meu tema responsável por isso.
\documentclass{beamer}
\usetheme{neo}
\begin{document}
\frame{
\begin{block}{}
Here is my text...
\end{block}
}
\end{document}
Responder1
Nova solução
Com a versão v0.5 do tema interno tcolorbox, você pode ativar/desativar o título vazio à vontade:
\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}
Solução Antiga
Imprima o título somente se não estiver vazio:
\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}
Outra solução (parcial)
Como esse problema não acontece para blocos arredondados, a ideia é utilizá-los, mas mudar sua definição para ter raio de canto igual a 0.
No código a seguir consertei o canto superior esquerdo (marcado com %%%% CHANGEDno código), os demais cantos ainda precisam ser consertados.
\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}
