Fix setting background

README.md

@@ -83,7 +83,7 @@ For a more detailed explanation of the standard installation process of packages
 
 ## License
 
-Copyright (C) 2019 by Tuomas Välimäki
+Copyright (C) 2019-2022 by Tuomas Välimäki
 
 This work may be distributed and/or modified under the conditions of the LaTeX Project Public License, either version 1.3 of this license or (at your option) any later version. The latest version of this license is in:
 

beamerthemetuni.dtx

@@ -1,6 +1,6 @@
 % \iffalse meta-comment ------------------------------------------------------
 %
-% Copyright (C) 2019 by Tuomas Välimäki
+% Copyright (C) 2019-2022 by Tuomas Välimäki
 %
 % This work may be distributed and/or modified under the
 % conditions of the LaTeX Project Public License, either
@@ -23,7 +23,7 @@
 % ------------------------------------------------------------------------ \fi
 % \iffalse
 %<*driver|package>
-\def\tuniversion{2019/07/29 v1.1}
+\def\tuniversion{2022/11/09 v1.2}
 %</driver|package>
 %<*internal>
 \def\nameofplainTeX{plain}
@@ -41,7 +41,7 @@
 
 This is a generated file.
 
-Copyright (C) 2019 by Tuomas Välimäki
+Copyright (C) 2019-2022 by Tuomas Välimäki
 
 This work may be distributed and/or modified under the
 conditions of the LaTeX Project Public License, either
@@ -401,22 +401,33 @@ and beamercolorthemetuni.sty.
 %
 % \begin{macro}{purple}
 %
-%   The color of the slide is inherited from the background of |normal text|,
-%   so we set that at the beginning of each slide. We define a key |purple| to
-%   change the slide background to purple, foreground to white, and structure
-%   to blue.
+%   \changes{v1.2}{2022/11/09}{Fix the way backgrounds are set}
+%
+%   The color of the slide is inherited from the background of |normal text|.
+%   We define a key |purple| to change the slide background to purple,
+%   foreground to white, and structure to blue.
+%
+%   In order to make this work, we need to patch |\setkeys| to be nestable.
 %
 %    \begin{macrocode}
-\BeforeBeginEnvironment{frame}{%
-  \setbeamercolor{normal text}{fg=black,bg=white}%
-  \usebeamercolor[fg]{normal text}%
-  \setbeamercolor{structure}{fg=tuniPurple}%
-}
+\let\my@setkeys@orig\setkeys
+\def\setkeys{\expandafter\my@setkeys@aux\expandafter{\KV@prefix}}
+\long\def\my@setkeys@aux#1#2#3{\my@setkeys@orig{#2}{#3}\def\KV@prefix{#1}}
+
+\newif\if@purpleFrame
 \define@key{beamerframe}{purple}[true]{%
+  \@purpleFrametrue
+  \begingroup
   \setbeamercolor{normal text}{fg=white,bg=tuniPurple}%
   \usebeamercolor[fg]{normal text}%
   \setbeamercolor{structure}{fg=tuniBlue}%
 }
+\pretocmd{\beamer@reseteecodes}{%
+  \if@purpleFrame
+    \endgroup
+    \@purpleFramefalse
+  \fi
+}{}{}
 %    \end{macrocode}
 % \end{macro}
 %