openPMD: Generalize Mesh Position (#1296)

This adds a small utility that returns the relative in-cell position of values
on each cell depending on an `amrex::MultiFab`'s `Box`'s `IndexType`.

This does not change the output of openPMD yet, since we spatially and
temporally center fields before output, but makes the routines
more general overall for future use.

1 files changed, 29 insertions, 0 deletions

diff --git a/Source/Utils/RelativeCellPosition.cpp b/Source/Utils/RelativeCellPosition.cpp
new file mode 100644
index 000000000..58c35fa52
--- /dev/null
+++ b/Source/Utils/RelativeCellPosition.cpp
@@ -0,0 +1,29 @@
+/* Copyright 2020 Axel Huebl
+ *
+ * This file is part of WarpX.
+ *
+ * License: BSD-3-Clause-LBNL
+ */
+#include "RelativeCellPosition.H"
+
+#include <AMReX_IndexType.H>
+
+
+std::vector< double >
+utils::getRelativeCellPosition(amrex::MultiFab const& mf)
+{
+    amrex::IndexType const idx_type = mf.ixType();
+
+    std::vector< double > relative_position(AMREX_SPACEDIM, 0.0);
+
+    // amrex::CellIndex::CELL means: 0.5 from lower corner for that index/direction
+    // amrex::CellIndex::NODE means: at corner for that index/direction
+    // WarpX::do_nodal means: all indices/directions on CellIndex::NODE
+    for (int d = 0; d < AMREX_SPACEDIM; d++)
+    {
+        if (idx_type.cellCentered(d))
+            relative_position.at(d) = 0.5;
+    }
+
+    return relative_position;
+}