Fix issue #52: set max width and height of images in default.beamer

default.beamer

@@ -66,25 +66,16 @@ $if(url)$
 \usepackage{url}
 $endif$
 $if(graphics)$
-\usepackage{graphicx}
-% Redefine \includegraphics so that, unless explicit options are
-% given, the image width will not exceed the width of the page.
-% Images get their normal width if they fit onto the page, but
-% are scaled down if they would overflow the margins.
+\usepackage{letltxmacro}
 \makeatletter
-\def\ScaleIfNeeded{%
-  \ifdim\Gin@nat@width>\linewidth
-    \linewidth
-  \else
-    \Gin@nat@width
-  \fi
-}
+\def\maxwidth{\ifdim\Gin@nat@width>\linewidth\linewidth\else\Gin@nat@width\fi}
+\def\maxheight{\ifdim\Gin@nat@height>\textheight0.8\textheight\else\Gin@nat@height\fi}
 \makeatother
-\let\Oldincludegraphics\includegraphics
-{%
- \catcode`\@=11\relax%
- \gdef\includegraphics{\@ifnextchar[{\Oldincludegraphics}{\Oldincludegraphics[width=\ScaleIfNeeded]}}%
-}%
+\AtBeginDocument{
+  \LetLtxMacro\Oldincludegraphics\includegraphics
+  \renewcommand{\includegraphics}[2][]{%
+    \Oldincludegraphics[#1,width=\maxwidth,height=\maxheight,keepaspectratio]{#2}}
+}
 $endif$
 
 % Comment these out if you don't want a slide with just the