rgl 1.3.1

Major changes

• sprites3d() now supports plotting different 3D symbols
  at each location (issue #406).

Minor changes

• ARIA support now declares rgl scenes with role = "img".
• The vignettes in this package now use
  markdown::html_format, so they no longer require Pandoc
  (though Pandoc-using output formats like html_document will still be supported).
• Christophe Geuzaine's GL2PS library (used by rgl.postscript())
  updated to version 1.4.2, and blending (transparency)
  has been enabled in formats that support it.
• The Makevars.ucrt file has been changed for compatibility
  with an upcoming change to Windows Rtools. (Pull request #412 submitted by Tomas Kalibera).

Bug fixes

• The ARIA support caused htmlwidgets::saveWidget() to fail when
  run in a Shiny session.
• text3d() and mtext3d() did not pass the cex argument to
  plotmath3d() (pull request #384).
• polygon3d() failed when given exactly 3 points (issue #388).
• snapshot3d() failed on Windows with some versions of webshot2 (issue #391).
• Fixed issues caused by misuse of dev.off() using new function
  safe.dev.off().
• Fixed issue with warning() call reported by CRAN.
• Smooth shapes were not rendered correctly by rglwidget().
  This was especially noticeable for spheres with fov = 0, but was present in other cases as well (issue #401).
• textype = "alpha" was not rendered correctly by rglwidget() (issue #408).
• setUserCallbacks() and related functions failed when
  the subscene argument was anything other than the root
  subscene.