LaTeX: add support for div.topic_box-decoration-break=slice

It is however undecided if the slice style should suppress the
horizontal shadow forcefully.  It does not so far.

This commit has removed the \spx@ShadowFBox macro which got so
simple that its meaning could be put directly into \FrameCommand
definition.

sphinx/texinputs/sphinx.sty

@@ -506,7 +506,7 @@ will be set to white}%
         #2%
         % MEMO: at 5.1.0 and up to 6.2.0, an \edef with \number\dimexpr was
         % used here.  Since 6.2.0, expansion is delayed to time of use as for
-        % the other dimensions handled above.  This is synced with an added
+        % the other dimensions handled above.  This is synched with an added
         % encapsulation in \dimexpr...\relax by the "setup" from
         % sphinxpackageboxes.sty.  An induced regression had to be fixed in
         % the sphinxShadowBox environment as it was using in an \ifdim the

sphinx/texinputs/sphinxlatexshadowbox.sty

@@ -23,15 +23,14 @@
         {topic}{sphinxtopicBorderColor}{sphinxtopicBgColor}{sphinxtopicShadowColor}%
 }%
 
-% At 5.1.0 the code formerly here has been refactored and incorporated
-% into more powerful \spx@boxes@fcolorbox from sphinxpackageboxes.sty
-% (which not only has a @rectangle variant but also @rounded)
-\long\def\spx@ShadowFBox#1{%
-  \leavevmode
-  \setbox\z@\hbox{#1}%
-  % \spx@shadowbox@boxes@fcolorbox@setup MUST have been called before
-  \spx@boxes@fcolorbox{\box\z@}%
-}
+% At 5.1.0 the code formerly here in a definition of \spx@ShadowFBox has been
+% refactored to hand over to a more powerful \spx@boxes@fcolorbox provided by
+% file sphinxpackageboxes.sty, it can draw rounded corners and add a background
+% color.
+
+% At 6.2.0, \spx@ShadowFBox is so much simplified that it is now not
+% separatedly defined but directly incorporated into the \FrameCommand
+% definition done by sphinxShadowBox environment below.
 
 % Use framed.sty \MakeFramed/\endMakeFramed to allow page breaks for topic
 % boxes.  Originally Sphinx used \shadowbox from fancybox.sty but it did not
@@ -56,7 +55,20 @@
    \spx@shadowbox@boxes@fcolorbox@setup
    % we will use the dimen registers from sphinxpackageboxes.sty which now hold
    % the values from options related to topic/contents
-   \def\FrameCommand {\spx@ShadowFBox }%
+   % MEMO: \spx@boxes@fcolorbox creates an \hbox but does not quit vertical
+   %       mode; but in context of framed.sty's \FrameCommand TeX is already
+   %       in restricted horizontal mode, so no need for a \leavevmode here.
+   \def\FrameCommand {\spx@boxes@fcolorbox}%
+   % 6.2.0 adds support for div.topic_box-decoration-break=slice.
+   % (it is yet undecided if slice style should inhibit a bottom shadow)
+   \ifspx@topic@border@open
+     \def\FirstFrameCommand
+               {\spx@boxes@fcolorbox@setup@openbottom\FrameCommand}%
+     \def\MidFrameCommand
+               {\spx@boxes@fcolorbox@setup@openboth  \FrameCommand}%
+     \def\LastFrameCommand
+               {\spx@boxes@fcolorbox@setup@opentop   \FrameCommand}%
+   \fi
    \advance\spx@image@maxheight
    -\dimexpr\spx@boxes@border@top+\spx@boxes@border@bottom
            +\spx@boxes@padding@top+\spx@boxes@padding@bottom