Feature request: hook to decode overlay specifications

[jlaurens]

Add some hook to patch overlay specifications management.

problem

Overlay specifications are absolute. Sometimes, one strongly prefers relative specifications.

For example, you can have 2 different tikz pictures that appear step by step in parallel, instead of one after the other. Step x of picture 1 may appear at the same time as step y of picture 2. Each time you add something new to be uncovered before the pictures, then you have to update both x and y.

Another example concerns sticky notes that appear above the text. Consider the situation where the note should be visible only when a sparse set of elements are uncovered. Each time elements are reordered, or new items are added, the sticky note specification should be updated accordingly.

My ugly solution

I currently have developed a package to add a layer over standard beamer overlay specifications. That works pretty well IMHO, but I had to hack \beamer@masterdecode to intercept the part between '<' and '>' and turn some extended syntax into normal beamer syntax.

The request

Add a hook in \beamer@masterdecode to allow some preflight management of its argument. Something like

1. rename actual \beamer@masterdecode into \beamer@rawmasterdecode
2. define \beamer@xtdmasterdecode to be something like

\def\beamer@xtdmasterdecode#1{
  \def\beamer@masterdecodearg{#1}
  \UseHookWithArguments{beamer/masterdecode/N}{1}{\beamer@masterdecodearg}
  \exp_args:NV \beamer@rawmasterdecode \beamer@masterdecodearg
}

Some switch to activate/deactivate this feature

\def\beamerxtdspecon{\def\beamer@masterdecode{\beamer@xtdmasterdecode}}
\def\beamerxtdspecoff{\def\beamer@masterdecode{\beamer@rawmasterdecode}}

and start with \beamerxtdspecoff

[samcarter]

To better understand the problem, can you add some example code of something which isn't already possible with the existing relative overlay specifications?

[josephwright]

I'm with @samcarter here - beamer has been around for ~20 years with the current relative specs, so we need a clear example of something that doesn't work

[jlaurens]

Never said that there is something that does not work or is not possible, I only said that I made some kind of improvement based on some awful hack and that hooks can avoid that hack. In short, I am looking for some plugin architecture and hooks seem a good starting point.
In next example, we want the "n+1", "n+2" and "n+3" in the tikzpicture be exactly the "n+1", "n+2" and "n+3" of the itemize environment. AFAIK, actual beamer relative overlay specifications strongly depend on what are the "...".

\documentclass{beamer}
\RequirePackage{tikz}
\begin{document}
\begin{frame}
...
\begin{itemize}
\item<n+1-> A
\item<n+2-> B
\item<n+3-> C
\end{itemize}
...
\begin{tikzpicture}
\visible<n+1->{\node at (0,0) {A};}
\visible<n+2->{\node at (0,1) {B};}
\visible<n+3->{\node at (1,0) {C};}
\end{tikzpicture}
\end{frame}
\end{document}

[samcarter]

You could use https://tex.stackexchange.com/a/50493/36296 to label the overlays

[jlaurens]

No problem I will stick to the hack