Support `ascii=true` option in `writevtk`

[eschnett]

It would be convenient if Griap's version of writevtk supported the ascii=true function of the WriteVTK writevtk function. This would help debugging. It would also allow testing Gridap's output in the VtkTests.jl test case.

[fverdugo]

Good point @eschnett !

In general, we want a way of passing all options supported by WriteVTK.vtk_grid.

The signature of Gridap.writevtk has to be modified with care in order to not mess up with the arguments redirected to visualization_data.

In file,

https://github.com/gridap/Gridap.jl/blob/master/src/Visualization/Vtk.jl

I would do something in this direction:

struct VtkOptions{T}
  kwargs::T
end
VtkOptions(;kwargs...) = VtkOptions(kwargs)

function writevtk(options::VtkOptions,args...;kwargs...)
  map(visualization_data(args...;kwargs...)) do visdata
    write_vtk_file(
    options,visdata.grid,visdata.filebase,celldata=visdata.celldata,nodaldata=visdata.nodaldata)
  end
end

# Needed for backwards compatibility
function writevtk(args...;kwargs...)
  writevtk(VtkOptions(compress=false),args...;kwargs...)
end

then propagate options until we reach the call to vtk_grid which now should be called as

vtkfile = vtk_grid(filebase, points, cells; options...)

[fverdugo]

From the user perspective when visualizing a FEFunction:

# Default options (like now)
writevtk(trian,"trian",cellfields=["uh"=>uh])

# Custom options
options = VtkOptions(compress=false,ascii=true)
writevtk(options,trian,"trian",cellfields=["uh"=>uh])

[fverdugo]

Idem for createvtk