How (and understanding) the editing of a beamertheme.sty to create bordered/framed blocks?

Question

I am trying to edit a beamerthemeMyTheme.sty file to have the exampleblock become framed/bordered. While I have seen examples such as that in

• Link to answer providing code for framed blocks (it does not work for me although I expect it should)
• Link to question regarding framed blocks (question providing framed block answers)
• Documentation of 'tcolorbox', and the documentation of tcolorbox provides many good examples on making framed blocks using the package, which I managed to do.

What I cannot seem to do is edit the style file to make each exampleblock a framed block with a specific frame color. At the moment I am continuously fumbling with the concepts of the style file layout and syntax present in this for ex:

\defbeamertemplateparent{blocks}[framed]{block begin,block end}[1][{[#1]}

What is the [framed] component doing here? Is it a parameter or a flag to specify a new usage of the block environment used? Is this overriding the block environment or when the word "blocks" is used instead? What are the parameters in [1][{[#1]} setting or referring to? Another statement in the first link above:

\defbeamertemplate{block begin}{framed}[1][]

Is this referring to every block that will be created or a block that will be flagged/set as "framed"? Again what is the number referring to?

This code produces a framed block using \usepackage{tcolorbox}:

\begin{frame}{test}
\begin{tcolorbox}[title=My title,
colback=red!5!white,
colframe=red!75!black,
fonttitle=\bfseries]
This is a tcolorbox
Further text.
\end{tcolorbox}
\end{frame}

Overall, I would like to understand how to create the theme style for adding framed blocks to exampleblocks, while understanding what the statements are doing. I have been trying to get through the book 'The TEXbook' by Donald E. Knuth, but I seem to be missing the big picture.

Answer 1

A theme definition is more complex than blocks definition, but if you just want to use framed blocks instead of default beamer blocks don't need to define a new theme, just define new blocks.

Following example shows how to define new tcolorboxes to use as example and alert blocks and respecting beamer defined colors for these blocks. There are geometric differences between default beamer and tcolorboxes, but they can be solved adding geometry options in boxes definition.

\documentclass{beamer}
\usepackage[most]{tcolorbox}
\usepackage{lmodern}

\usetheme{Warsaw}

\newtcolorbox{myexampleblock}[2][]{%
colframe = block title example.bg,
coltitle = block title example.fg,
colback = block body example.bg,
title = #2,
#1
}

\newtcolorbox{myalertblock}[2][]{%
colframe = block title alerted.bg,
coltitle = block title alerted.fg,
colback = block body alerted.bg,
title = #2,
#1
}

\begin{document}

\begin{frame}
\begin{exampleblock}{Example}
this a beamer block example
\end{exampleblock}

\begin{myexampleblock}{Example}
this a framed block example
\end{myexampleblock}

\begin{alertblock}{Alert}
this a beamer alerted block
\end{alertblock}

\begin{myalertblock}{Alert}
this a framed alerted block 
\end{myalertblock}
\end{frame}

\end{document}

Update:

In order to create a beamertheme file with these definitions, we extract all of them (and packages?) into beamerthemeTest.sty file and leave it into the working folder.

% beamerthemeTest.sty
\RequirePackage[most]{tcolorbox}

\usetheme{Warsaw}

\newtcolorbox{myexampleblock}[2][]{%
colframe = block title example.bg,
coltitle = block title example.fg,
colback = block body example.bg,
title = #2,
#1
}

\newtcolorbox{myalertblock}[2][]{%
colframe = block title alerted.bg,
coltitle = block title alerted.fg,
colback = block body alerted.bg,
title = #2,
#1
}

Now main file looks like:

\documentclass{beamer}

\usetheme{Test}

\begin{document}

\begin{frame}
\begin{exampleblock}{Example}
this a beamer block example
\end{exampleblock}

\begin{myexampleblock}{Example}
this a framed block example
\end{myexampleblock}

\begin{alertblock}{Alert}
this a beamer alerted block
\end{alertblock}

\begin{myalertblock}{Alert}
this a framed alerted block 
\end{myalertblock}
\end{frame}

\end{document}

Answer 2

You don't need to create a new theme to get borders around your blocks.

Instead you can use the new tcolorbox inner theme (https://www.ctan.org/pkg/beamertheme-tcolorbox ) and tweak things from there:

\documentclass{beamer}

\usetheme{Warsaw}
\useinnertheme{tcolorbox}

\makeatletter
\tcbset{
 boxrule=1pt,
 frame style={draw,beamer@tcb@titlebg}
}
\makeatother

\begin{document}

\begin{frame}
\begin{block}{Block}
this a beamer block
\end{block}

\begin{exampleblock}{Example}
this a framed block example
\end{exampleblock}

\begin{alertblock}{Alert}
this a beamer alerted block
\end{alertblock}

\end{frame}

\end{document}

Answer 3

I am not sure I understood the whole question. I may help as far as the setbeamertemplateparent is concerned.

From beamer's manual :

    \defbeamertemplateparent{⟨parent template name⟩}[⟨predefined option name⟩]{⟨child template list⟩}[⟨argument number⟩][⟨default optional argument⟩]{⟨arguments for children⟩}

The effect of this command is that whenever someone calls \setbeamertemplate{⟨parent template name⟩}{⟨args⟩}, the command \setbeamertemplate{⟨child template name⟩}{⟨args⟩} is called for each ⟨child template name⟩ in the ⟨child template list⟩.

So, in

\defbeamertemplateparent{blocks}[framed]{block begin,block end}[1][{[#1]}

the «framed» is a predefined option name and the [1] means there is only one argument. I prefer not to dig dipper in understanding the whole statement, since I may get wrong. I understand however that your defbeamertemplate example works only for blocks that are flagged as framed.

I also think beamer manual will be more helpful that Knuth's book for this peculiar question.