Mesh-Readers.txt

The unstructured mesh analyzer interacts with disk files through an
interface, defined in GMGW_FileWrapper.hxx.  To create a file reader for
a new file format, you must implement these functions:

void scanFile();

void seekStartOfConnectivity() const;
void getNextCellConnectivity(int& nConn, unsigned int connect[]) const;
void getNextVertexCoords(double& x, double& y, double& z) const;

You must also add an entry in the FileWrapper::factory function to be
able to create the new reader at run time.

What scanFile must do
---------------------

scanFile must

1. Set the number of entities of each time (vertices, bdry
triangles, bdry quadrilaterals, tetrahedra, pyramids, prisms, and
hexahedra).

2. Provide offsets into the file for the starting points of vertex
coordinates and connectivity, so that subsequent calls can seek directly
to those locations at need.

3. Set up arrays (in the FileWrapper base class) that identify the type
of each cell (including bdry faces; these use the VTK cell type
enumeration, replicated in GMGW_unst.hxx), whether a cell is a bdry
face, and whether a vertex is a bdry vertex.

What seekStartOfConnectivity must do
------------------------------------

seekStartOfConnectivity is a virtual function with a definition in the
FileWrapper base class.  The base class definition moves to the stored
location of the start of the connectivity in the input file.  Derived
class versions can add other initialization work that is required before
starting to read connectivity, as needed; for UGRID files, this is
needed, but not for VTK files, for instance.

What getNextCellConnectivity must do
------------------------------------

At the beginning of a call to getNextCellConnectivity, the input file is
positioned to read a cell's connectivity data.  The function must read
this data (including adjusting enddianness, as needed), and return the
number of vertices the cell is connected to and the indices of those
vertices in canonical order.  (Note: this canonical order corresponds to
VTK ordering, not UGRID ordering; UGRID numbers vertices of pyramids
differently from other storage formats.)  Finally, at exit, the input
file must be positioned to read whatever follows the current cell's
connectivity.

What getNextVertexCoords must do
--------------------------------

At the beginning of a call to getNextVertexCoords, the input file is
positioned to read a vertex's coordinates.  The function must read and
return this data (including adjusting enddianness, as needed).  Finally,
at exit, the input file must be positioned to read whatever follows the
current vertex's coordinates.