moved voxel plot to api accessible function

scripts/openmc-voxel-to-vtk

@@ -2,63 +2,7 @@
 
 from argparse import ArgumentParser
 
-import h5py
-import vtk
-
-_min_version = (2, 0)
-
-
-def voxel_to_vtk(voxel_file: str, output: str):
-
-    # Read data from voxel file
-    fh = h5py.File(voxel_file, "r")
-
-    # check version
-    version = tuple(fh.attrs["version"])
-    if version < _min_version:
-        old_version = ".".join(map(str, version))
-        min_version = ".".join(map(str, _min_version))
-        err_msg = (
-            "This voxel file's version is {}. This script "
-            "only supports voxel files with version {} or "
-            "higher. Please generate a new voxel file using "
-            "a newer version of OpenMC.".format(old_version, min_version)
-        )
-        raise ValueError(err_msg)
-
-    dimension = fh.attrs["num_voxels"]
-    width = fh.attrs["voxel_width"]
-    lower_left = fh.attrs["lower_left"]
-
-    nx, ny, nz = dimension
-
-    grid = vtk.vtkImageData()
-    grid.SetDimensions(nx + 1, ny + 1, nz + 1)
-    grid.SetOrigin(*lower_left)
-    grid.SetSpacing(*width)
-
-    # transpose data from OpenMC ordering (zyx) to VTK ordering (xyz)
-    # and flatten to 1-D array
-    print("Reading and translating data...")
-    h5data = fh["data"][...]
-
-    data = vtk.vtkIntArray()
-    data.SetName("id")
-    # set the array using the h5data array
-    data.SetArray(h5data, h5data.size, True)
-    # add data to image grid
-    grid.GetCellData().AddArray(data)
-
-    writer = vtk.vtkXMLImageDataWriter()
-    if vtk.vtkVersion.GetVTKMajorVersion() > 5:
-        writer.SetInputData(grid)
-    else:
-        writer.SetInput(grid)
-    if not output.endswith(".vti"):
-        output += ".vti"
-    writer.SetFileName(output)
-    print("Writing VTK file {}...".format(output))
-    writer.Write()
+import openmc
 
 
 if __name__ == "__main__":
@@ -73,4 +17,6 @@ if __name__ == "__main__":
         help="Path to output VTK file.",
     )
     args = parser.parse_args()
-    voxel_to_vtk(args.voxel_file, args.output)
+    print("Reading and translating data...")
+    openmc.plots._voxel_to_vtk(args.voxel_file, args.output)
+    print(f"Written VTK file {args.output}...")