Hey!
Yes, I ended up getting it to work, I included an example script here, perhaps of interest:
Summary
Same script
#https://www.analytech-solutions.com/analytech-solutions/blog/binary-io.html
using XML
using XML: Document, Declaration, Element, Text
using StaticArrays
### Functions=================================================
# Function to create a DataArray element for VTK files
function create_data_array_element(name::String, data::AbstractVector{T}, offset::Int) where T
# Create the DataArray elements
dataarray = Element("DataArray")
# Set attributes based on the input vector's type
dataarray.attributes["type"] = string(eltype(first(data)))
dataarray.attributes["Name"] = name
dataarray.attributes["NumberOfComponents"] = string(Int(sizeof(first(data))/sizeof(eltype(first(data)))))
dataarray.attributes["format"] = "appended"
dataarray.attributes["offset"] = string(offset)
return dataarray
end
###===========================================================
# Points = [SVector{3,Float64}(1,2,3), SVector{3,Float64}(4,5,6)]
# Kernel = Float64.([100, 200])
# KernelGradient = [SVector{3,Float64}(-1,1,0), SVector{3,Float64}(1,-1,0)]
N = 6195
Points = rand(SVector{3,Float64},N) * 10
Kernel = rand(Float64,N) * 1000
KernelGradient = rand(SVector{3,Float64},N) * 100
function PolyDataTemplate(filename::String, points, variable_names, args...)
# Generate the XML document and then put in some fixed values
xml_doc = Document(Declaration(version=1.0,encoding="utf-8"))
vtk_file = Element("VTKFile")
vtk_file.attributes["type"] = "PolyData"
vtk_file.attributes["version"] = "1.0"
vtk_file.attributes["byte_order"] = "LittleEndian"
vtk_file.attributes["header_type"] = "UInt64"
# PolyData is the main section, filling it out
polydata = Element("PolyData")
piece = Element("Piece")
N = length(points)
piece.attributes["NumberOfPoints"] = string(N)
# This Points element and its associated DataArray has to be constructed individually
points_element = Element("Points")
point_dataarray = create_data_array_element("Points",points,0)
point_dataarray["offset"] = 0
# Generate appended data element
appendeddata = Element("AppendedData")
appendeddata.attributes["encoding"] = "raw"
# Start writing the file and generating the correct dataarrays with the right offsets in the loop
NB = 0
io = IOBuffer()
write(io,"\n_")
UncompressedHeaderN = N * length(first(points)) * sizeof(typeof(first(points)))
NB += write(io, UncompressedHeaderN)
NB += write(io, points)
# Generate XML tags for kwargs data
pointdata = Element("PointData")
dataarrays = Vector{XML.Node}(undef,length(args))
for i in eachindex(args)
arg = args[i]
dataarrays[i] = create_data_array_element(variable_names[i],arg,NB)
A = typeof(first(arg))
T = eltype(A)
Ni = length(arg)
Tsz = sizeof(T)
Nc = Int( sizeof(A) / Tsz )
HowManyBytes = Tsz*Nc*Ni + Tsz
NB += HowManyBytes
write(io, NB)
write(io, arg)
end
# Take the result from the buffer, turn to string and write it
v = take!(io)
t = Text(String(v))
write(io,"\n")
push!(appendeddata,t)
close(io)
# Glue all xml pieces together
push!(xml_doc,vtk_file)
push!(points_element,point_dataarray)
push!(piece,points_element)
push!(polydata,piece)
push!(vtk_file,polydata)
map(x -> push!(pointdata,x), dataarrays)
push!(piece,pointdata)
push!(vtk_file,appendeddata)
XML.write(filename,xml_doc)
end
save_location = raw"E:\SPH\TestOfFile.vtp"
d = @report_opt target_modules=(@__MODULE__,) PolyDataTemplate(save_location, Points, ["Kernel", "KernelGradient"], Kernel, KernelGradient)
println(d)
@profview PolyDataTemplate(save_location, Points, ["Kernel", "KernelGradient"], Kernel, KernelGradient)
b = @benchmark PolyDataTemplate($save_location, $Points, $(["Kernel", "KernelGradient"]), $Kernel, $KernelGradient)
display(b)
@code_warntype PolyDataTemplate(save_location, Points, ["Kernel", "KernelGradient"], Kernel, KernelGradient)
PolyDataTemplate(save_location, Points, ["Kernel", "KernelGradient"], Kernel, KernelGradient)
It is about 10% faster than WriteVTK, with same memory foot-print, but lot less flexibility etc. only this one format the way I want 
I was not able to figure out how to nicely preallocate the whole file and buffer and then directly update the buffer to avoid allocs when using XML.jl so I took a break from it…
Let me know what you think, quite curious about your opinion
Kind regards