[vtkusers] C interface to write VTK XML files

[Mathieu Malaterre]

Full documentation can be found in:

VTK/IO/vtkXMLWriterC.h
VTK/IO/vtkXMLWriterC.cxx

A simple test of writing a timestep cube can be found at:

VTK/IO/Testing/Cxx/TestXMLCInterface.c
-------------------------------------------

The basic idea was to provide an OO-like C interface to access the 
vtkXML*Writer classes. The C interface hold a reference to the 
vtkDataSet you are writting. So the main difference between a C++ code 
and the equivalent C code is that you are passing structure directly to 
the writer (instead of creating a vtkDataSet).

For example the C++ code:

vtkXMLWriter *writer = vtkXMLWriter::New();
vtkUnstructuredGrid *ug = vtkUnstructuredGrid::New();
writer->SetInput( ug );
writer->SetFileName( "bla.vtu" );
ug->SetPoints( mypoints );
...
writer->Write();

becomes:

vtkXMLWriterC* writer = vtkXMLWriterC_New();
/* #define VTK_UNSTRUCTURED_GRID               4 */
vtkXMLWriterC_SetDataObjectType(writer, 4);
vtkXMLWriterC_SetFileName(writer, "bla.vtu");
vtkXMLWriterC_SetPoints(writer, 10, mypoints_raw_pointer, NPOINTS);
...
vtkXMLWriterC_Write(writer);



Mathieu