Letting Embedded Boundary work with AMRcore model mainly in Fortran interface

[paradoxknight1]

Dear community,

I'm currently working with the fortran interface amrcore model. And there is a requirement of implement the Embedded Boundary function.
Based on the docuemnt, it seems that to build a Embedded Boundary, the Geometry object is needed. However, through the usage of amrcore model, the geom, BoxArrays, and DistributionMapping are both automatically building through the C++ part of the AMRmesh model.
The thing I would like to ask is that if it is possible to build the embedded boundary in the Fortran's inherit virtual functions.

What's more, as it mentioned in #3645.
"Usually one calls EB2:Build with the Geometry at the max level at the beginning." What exactly is the max level? As the Geometry in Amrcore is build automatically.
Is it possible to build a geometry seperately aginest the Amrcore framework?

Many thanks.

[WeiqunZhang]

If you are willing to write some codes in C++, yes you can build Embedded Boundary in a Fortran code.

Re: your questions about max level and Geometry, let's suppose you are using amrex_amrcore_module. That module has type(c_ptr) :: amrcore. On the Fortran side, you can call a C++ function (written by you) and pass that pointer to the C++ side. That pointer is amrex::AmrCore*. Then you have everything you need regarding max level, Geometry, etc.

[WeiqunZhang]

I think you want to initialize EB after amrex_amrcore_init but before my_amr_init so that my_amr_init can use EB.

[paradoxknight1]

Thanks for your help.
Here is another problem from the C++ and Fortran Interface: To fill the cut cell's value about the embedded boundary, a huge amount of information from the EB module is needed. Apart from EBcellFlagFab, which could be transferred to the Fortran Interface as an integer matrix, volume fraction, and normal vector are both needed. However, they are MultiCut objects, which are not defined on the Fortran side.
There are two options from my perspective,

1. Transfer the MFI object to C++, which builds a CutFab object, which could then be transferred as a Real matrix to Fortran.
2. If the MultiCutFab object could be converted as a MultiFab tand hen converted to the Fortran side? Since it only has data on boxes that contain cut cells, just need to handle it carefully.

Many thanks for your kind help.

[paradoxknight1]

May I check which option is available.
For the first option, I'm not sure if the Mfiter object could be transferred directly from C++ to Fortran, as their definition might be different.
For the second option, I'm not sure if it is OK for the transfer from MultiCutFab to MultiFab.

[WeiqunZhang]

amrex_mfiter in Fortran is

  type, public :: amrex_mfiter
     type(c_ptr)      :: p       = c_null_ptr
     ...     

That p is a C pointer to amrex::MFIter.

MultiCutFab has a member function ToMultiFab you can use. For example

MultiFab centroid = ebfactory.getCentroid().ToMultiFab();

[WeiqunZhang]

To get that MultiFab to the Fortran side, you need an object on the heap. So you probably need to do something like

MultiFab* p_centroid_mf = new MultiFab(ebfactory.getCentroid().ToMultiFab());