Providing override key work allows for extra checking
that the function signatures are correct.

https://stackoverflow.com/questions/39932391/virtual-override-or-both-c?answertab=active#tab-top

In the derived class the function is virtual by way of having the ¹same
type as the base class function.

However, an override can help avoid bugs by producing a compilation
error when the intended override isn't technically an override. E.g.
that the function type isn't exactly like the base class function. Or
that a maintenance of the base class changes that function's type, e.g.
adding a defaulted argument.

In the same way, a virtual keyword in the derived class can make such a
bug more subtle, by ensuring that the function is still virtual in
further derived classes.

The general advice is,
     -Use virtual for the base class function declaration.
      This is technically necessary.

     -Use override (only) for a derived class' override.
      This helps maintenance.

Now that VTK requires a C++11 compiler we can ditch using custom typedefs to
wrap =delete;

generated via:
cd $VTKSRC
perl Utilities/Doxygen/doc_header2doxygen.pl --to ~/tmp/vtkheaders .
cp -r ~/tmp/vtkheaders/* .

vtk(.*)\(const vtk\1&\);\s*//\s*Not implemented[\.]*
to
vtk\1(const vtk\1\&) VTK_DELETE_FUNCTION;

vtk(.*)\(const vtk\1 &\);\s*//\s*Not implemented[\.]*
to
vtk\1(const vtk\1 \&) VTK_DELETE_FUNCTION;

vtk(.*)\( const vtk\1 & \);\s*//\s*Not implemented[\.]*
to
vtk\1( const vtk\1 \& ) VTK_DELETE_FUNCTION;

vtk(.*)\( const vtk\1& \);\s*//\s*Not implemented[\.]*
to
vtk\1( const vtk\1\& ) VTK_DELETE_FUNCTION;

vtk(.*) \(const vtk\1&\);\s*//\s*Not implemented[\.]*
to
vtk\1 (const vtk\1\&) VTK_DELETE_FUNCTION;

(operator\s*=.*);\s*//\s*Not\s*implemented[\.]*
to
\1 VTK_DELETE_FUNCTION;

After that, this finds basically nothing:

operator.*implemented

then manually reverted changed files in VPIC and KWSys folders.

Perl was used to remove all the BTX and ETX markers from the code.
The specific command that was run on all "vtk*.h" files was this:
    perl -0777 -i -pe 's/(\n* *\/\/ *[BE]TX *\n+)+/\n\n/g'

This regex replaces each BTX/ETX line, plus any leading or trailing
blank lines, with a single blank line.

Code extracted from:

    https://gitlab.kitware.com/third-party/proj.git

at commit 41bdf05361007f8c5186f3df9944d86bb273ed13 (for/vtk).

Used the following command:

find . \( -iname *.h -and -type f \) -exec perl -pi -w -e 's/__vtk(.*)_h/vtk$1_h/g;' {} \;

Fixes many, but not all, clang -Wreserved-id-macro warnings.

Change-Id: I694ff053cb204c70e37b261296f496064d91fc07

The CVS $Revision$ keyword replacement will no longer maintain these
macros automatically.  They were used only to implement CollectRevisions
and vtkObjectBase::PrintRevisions, an API that was never used.

Automated as follows:

  pass 0:
  catch templates
  ---------------
  $ git grep 'vtk\(Cxx\|Type\)RevisionMacro' | grep '<'

  pass 1:
  main changes
  ---------------
  $ git grep -l '^vtkCxxRevisionMacro' | while read file; do
    echo "$file" 1>&2
    perl -i -ne 'print unless (/^vtkCxxRevisionMacro/ and /\)/)' $file
  done
  $ git grep -l -e 'vtkTypeRevisionMacro(' | while read file; do
    echo "$file" 1>&2
    perl -i -pe 's/vtkTypeRevisionMacro/vtkTypeMacro/g' $file
  done

  pass 2:
  verify
  ---------------
  $ git grep 'vtk\(Cxx\|Type\)RevisionMacro'

Fixed multi-line vtkCxxRevisionMacro and templates by hand.

The CVS $Revision$ keyword replacement will no longer maintain these
macros automatically.  They were used only to implement CollectRevisions
and vtkObjectBase::PrintRevisions, an API that was never used.

Automated as follows:

  pass 0:
  catch templates
  ---------------
  $ git grep 'vtk\(Cxx\|Type\)RevisionMacro' | grep '<'

  pass 1:
  main changes
  ---------------
  $ git grep -l '^vtkCxxRevisionMacro' | while read file; do
    echo "$file" 1>&2
    perl -i -ne 'print unless (/^vtkCxxRevisionMacro/ and /\)/)' $file
  done
  $ git grep -l -e 'vtkTypeRevisionMacro(' | while read file; do
    echo "$file" 1>&2
    perl -i -pe 's/vtkTypeRevisionMacro/vtkTypeMacro/g' $file
  done

  pass 2:
  verify
  ---------------
  $ git grep 'vtk\(Cxx\|Type\)RevisionMacro'

Fixed multi-line vtkCxxRevisionMacro and templates by hand.

BUG: Adding VTK_USE_CHARTS to VTKConfig.cmake.in. ENH: Adding a 2D graph layout example for context items.

This is an initial import of the surviving parts of the 2D drawing API I
have been working on, along with a prototype for a 2D scene and some chart
elements. This work is experimental, and parts of the API will be moved into
Rendering.

The API is subject to change and/or removal.