I need to create a visual effect in Beamer wherein the content of a slide is "greyed out" (or covered with a while translucent box), and a single emphasized bullet point is presented over the slide content. This effect should be compatible with any animations using the itemize or overprint features. I am using the Rochester theme. So far, it seems like there should be a way to do this using textblock, but I'm open to any succinct solution that achieves the desired effect.
There is an answer partially addressing this here. However, the accepted answer does not work for my use case because (1) beamer inserts a colored title bar on the examplebox, even if I leave the title empty (a bug?). (2) I need the box to be translucent (solved here), and (3) I need the block to cover the entirety of the slide content excluding the header.
I'm having a lot of trouble understanding solutions to similar questions posted elsewhere, because they use TikZ. For me, TikZ too obtuse and verbose to be maintainable, so I would strongly prefer a solution that uses textblock (similar to this example). If for some reason TikZ is necessary, it would be good if the TikZ source could be wrapped in some macros/functions and sequestered in a separate file, to avoid maintainability issues. I won't be able to modify or debug TikZ code. I need an "out of the box" solution. If this isn't possible, I will simply forgo having the desired effect.
This is as far as I've gotten with an example:
\documentclass[svgnames,professionalfont,13pt]{beamer}
\usepackage[utf8x]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english]{babel}
\usetheme{Rochester}
% https://tex.stackexchange.com/questions/59826/position-an-exampleblock-in-front-of-content
% for overlays
\usepackage{lipsum} % <= to insert dummy text
\usepackage[absolute,overlay]{textpos}
% get translucent block
\addtobeamertemplate{block begin}{\pgfsetfillopacity{0.5}}{\pgfsetfillopacity{1}}
\addtobeamertemplate{block alerted begin}{\pgfsetfillopacity{0.5}}{\pgfsetfillopacity{1}}
\addtobeamertemplate{block example begin}{\pgfsetfillopacity{0.5}}{\pgfsetfillopacity{1}}
\begin{document}
% Begin example slide
\setbeamercolor{background canvas}{bg=red}
\begin{frame}{title}
\begin{itemize}
\item<1->Point 1
\item<2->Point 2
\item<3->Point 3
\item<4->Point 4
\item<5->Point 5
\item<6->Point 6
\end{itemize}
\begin{exampleblock}{}
\begin{itemize}
\item The block needs to overlap the slide text
\item The colored title bar needs to be gone
\item I need this box to pop up only at the end
\item The block needs to be horizontally and vertically centered
\item The block needs to be as wide as the page
\item The block needs to be as tall as the slide, excluding the title area
\end{itemize}
\end{exampleblock}
\end{frame}
\end{document}
Edit: Mike Renfro's answer is almost complete. I've managed to work it into a form that is very close to what I want, posted below. The last trick will be getting the overlay to match the height and position of the slide body, and reproducing the slide margins within the overlay. I fear I'm not a very experienced LaTeX coder, so my modifications are quite sloppy. However, I think this illustrates what I'm trying to achieve:
\documentclass[svgnames,professionalfont,13pt]{beamer}
\usepackage[utf8x]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english]{babel}
\usetheme{Rochester}
\usepackage[absolute,overlay]{textpos}
\newcommand{\fadeslide}[1]{%https://tex.stackexchange.com/a/80496
\setlength{\TPHorizModule}{\paperwidth}\setlength{\TPVertModule}{\paperheight}
\begin{textblock*}{\paperwidth}[0.5,0.5](0.5\paperwidth,0.5\paperheight)
\setbeamercolor{postit}{bg=yellow}
\pgfsetfillopacity{0.8}
\begin{beamercolorbox}[sep=1em,wd=\textwidth]{postit}
\strut\vspace{13em}\strut% somehow fill the required vertical space?
\end{beamercolorbox}
\end{textblock*}
\pgfsetfillopacity{1}
% Simply repeating the solution again with opaque text
\begin{textblock*}{\paperwidth}[.5,0.5](0.5\paperwidth,0.5\paperheight)
\setbeamercolor{postit}{fg=black}
\pgfsetfillopacity{1}
\begin{beamercolorbox}[sep=1em,wd=\textwidth]{postit}
#1%CONTENT HERE
\end{beamercolorbox}
\end{textblock*}
}
\begin{document}
\setbeamercolor{background canvas}{bg=green}
\begin{frame}{title}
This is some content, we should show it first, and then occlude it.
\only<2->{
\fadeslide{
\begin{itemize}
\item This is almost correct! ( :
\item But it would be even better if the faded region covered the whole slide
\item And if this content were aligned similar to the slide content
\item I fear I don't really understand the solution code enough to achieve this
\end{itemize}
}}
\end{frame}
\setbeamercolor{background canvas}{bg=yellow}
\begin{frame}{title}
The overlay should shade the whole slide, like this.
(also showing the slide content below via transparency).
The overlaid text should be aligned like this text.
\end{frame}
\end{document}
