LaTeX: optional rounded corners for framing of code-blocks

Via a new configuration verbatimradius of 'sphinxsetup', which defaults
to 0pt.

If this dimension is non zero, the LaTeX package pict2e will be loaded
to help construct frames with rounded corners for code-blocks.  And if
the LaTeX package pict2e was not found, a LaTeX warning is issued during
PDF build.

doc/conf.py

@@ -74,6 +74,11 @@ latex_elements = {
              {\footnotesize\raggedright\printindex}
              {\begin{sphinxtheindex}\end{sphinxtheindex}}
 ''',
+    'sphinxsetup': """%
+VerbatimColor={RGB}{242,242,242},%
+VerbatimBorderColor={RGB}{32,32,32},%
+verbatimradius=3pt%
+""",
 }
 latex_show_urls = 'footnote'
 latex_use_xindy = True

doc/latex.rst

@@ -8,8 +8,11 @@ LaTeX customization
 
    \begingroup
    \sphinxsetup{%
-         verbatimwithframe=false,
+         verbatimborder=2pt,
+         verbatimsep=5pt,
+         verbatimradius=5pt,
          VerbatimColor={named}{OldLace},
+         VerbatimBorderColor={named}{Gold},
          TitleColor={named}{DarkGoldenrod},
          hintBorderColor={named}{LightCoral},
          attentionborder=3pt,
@@ -580,8 +583,17 @@ start of the chapter::
 
      \begingroup
      \sphinxsetup{%
-           verbatimwithframe=false,
+           % These were used as defaults for the whole sphinx.pdf
+           % VerbatimColor={RGB}{242,242,242},%
+           % VerbatimBorderColor={RGB}{32,32,32},%
+           % verbatimradius=3pt,%
+           % New definitions for this chapter code-blocks only:
            VerbatimColor={named}{OldLace},
+           VerbatimBorderColor={named}{Gold},
+           verbatimradius=5pt,
+           verbatimsep=5pt,
+           verbatimborder=2pt,
+           % Other configuration for this chapter only:
            TitleColor={named}{DarkGoldenrod},
            hintBorderColor={named}{LightCoral},
            attentionborder=3pt,
@@ -593,7 +605,8 @@ start of the chapter::
            cautionBorderColor={named}{Cyan},
            cautionBgColor={named}{LightCyan}}
 
-The below is included at the end of the chapter::
+And this is placed at the end of the chapter source to end the scope of
+the configuration::
 
   .. raw:: latex
 
@@ -839,6 +852,32 @@ Do not use quotes to enclose values, whether numerical or strings.
 
     Default: ``\fboxrule``
 
+``verbatimradius``
+    The radius of the rounded corners of the frame around :rst:dir:`code-block`\ s.
+
+    Default: ``0pt``
+
+    .. versionadded:: 5.1.0
+
+       If non-zero, it will trigger the loading of LaTeX package pict2e_.
+
+       .. caution::
+
+          The interface will remain experimental during the 5.x cycle: the
+          feature itself will remain, but the interface may evolve to include
+          other display elements such as admonitions.  For the latter it is
+          actually already possible for LaTeX-expert Sphinx users to use
+          functionalities of LaTeX packages such as tcolorbox_, via
+          redefinitions of the ``sphinxheavybox`` and ``sphinxlightbox``
+          `Environments`_.  This would be more difficult for code-blocks, and
+          this key achieves it.  The pict2e_ interface to some basic PDF
+          graphics operations is much more light-weight than the pgf_
+          framework used by tcolorbox_.
+
+    .. _pict2e: https://ctan.org/pkg/pict2e
+    .. _tcolorbox: https://ctan.org/pkg/tcolorbox
+    .. _pgf: https://ctan.org/pkg/pgf
+
 ``shadowsep``
     The separation between contents and frame for :dudir:`contents` and
     :dudir:`topic` boxes.