From 2e6ae2ef9bb230930f5213c256e624080b08faca Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Wed, 16 Apr 2025 16:49:14 +0200
Subject: Trying to make a cleaner  vtk writer

---
 c++/collision.hpp          |  17 ++++++-
 c++/examples/cavity_2d.cpp |  12 ++++-
 c++/write_vtk.hpp          | 112 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 138 insertions(+), 3 deletions(-)
 create mode 100644 c++/write_vtk.hpp

diff --git a/c++/collision.hpp b/c++/collision.hpp
index 87187c2..ba35be1 100644
--- a/c++/collision.hpp
+++ b/c++/collision.hpp
@@ -14,15 +14,30 @@ class component<T, Descriptor, cmpt::BGK> {
 public:
 	using Component = cmpt::BGK;
 
+	/**
+	 * Thoughts regarding automating order setup
+	 */
 	using access = cmpt::access_tuple<
 		cmpt::access<"dfs", 1, true, true, true>
 	>;
 
+	/**
+	 * Thoughts regarding automating order setup
+	 */
 	static constexpr saw::string_literal name = "collision";
 	static constexpr saw::string_literal after = "";
 	static constexpr saw::string_literal before = "streaming";
 
-	void apply(saw::data<sch::CellField>& field){
+	/**
+	 * Raw setup
+	 */
+	void apply(saw::data<sch::CellField>& field, saw::data<sch::FixedArray<sch::UInt64,Descriptor::D>> index, uint64_t time_step){
+		bool is_even = ((time_step % 2) == 0);
+		auto& cell = field.at(index);
+
+		auto& dfs_old = is_even ? cell.template get<"dfs_old">() : cell.template get<"dfs">();
+		auto& dfs = (!is_even) ? cell.template get<"dfs_old">() : cell.template get<"dfs">();
+
 
 	}
 };
diff --git a/c++/examples/cavity_2d.cpp b/c++/examples/cavity_2d.cpp
index 88a7702..0a8e9b1 100644
--- a/c++/examples/cavity_2d.cpp
+++ b/c++/examples/cavity_2d.cpp
@@ -71,6 +71,9 @@ void compute_rho_u (
 	vel[1] /= rho;
 }
 
+/**
+ * Unsure if feasible. I would have a rho normalization on the dfs and then I would use the const rho_computation
+ */
 template<typename Desc>
 void compute_const_rho_u (
 		saw::data<sch::DfCell<Desc>>& dfs,
@@ -80,15 +83,20 @@ void compute_const_rho_u (
 {
 	using dfi = df_info<sch::T, Desc>;
 
+	saw::native_data_type<sch::T>::type real_rho = 0;
 	std::fill(vel.begin(), vel.end(), 0);
 
 	for(size_t i = 0; i < Desc::Q; ++i){
+		real_rho += dfs(i).get();
 		vel[0] += dfi::directions[i][0] * dfs(i).get();
 		vel[1] += dfi::directions[i][1] * dfs(i).get();
 	}
+	for(size_t i = 0; i < Desc::Q; ++i){
+		dfs(i).set(dfs(i).get() * (rho/real_rho));
+	}
 
-	vel[0] /= rho;
-	vel[1] /= rho;
+	vel[0] *= real_rho / (rho*rho)
+	vel[1] *= real_rho / (rho*rho)
 }
 
 /**
diff --git a/c++/write_vtk.hpp b/c++/write_vtk.hpp
new file mode 100644
index 0000000..7bde854
--- /dev/null
+++ b/c++/write_vtk.hpp
@@ -0,0 +1,112 @@
+#pragma once
+
+#include <forstio/error.hpp>
+
+namespace kel {
+namespace lbm {
+namespace impl {
+
+template<typename... MemberTypes, saw::string_literal... MemberNames>
+struct lbm_vtk_writer<sch::Struct<MemberTypes,MemberNames>...> {
+
+	saw::error_or<void> apply(){
+		return saw::make_void();
+	}
+};
+
+template<typename CellFieldSchema>
+struct lbm_vtk_writer {
+};
+
+template<typename Desc, typename... StructT, saw::string_literal... StructN>
+struct lbm_vtk_writer<CellField<Desc,Struct<Member<StructT,StructN>...>>> {
+	template<uint64_t i>
+	saw::error_or<void> write_i(std::ofstream& vtk_file, const saw::data<CellField<Desc,Struct<Member<StructT,StructN>...>>>& field){
+
+		// vtk_file<<
+
+		return saw::make_void();
+	}
+
+	template<uint64_t i>
+	saw::error_or<void> iterate_i(std::ofstream& vtk_file, const saw::data<CellField<Desc,Struct<Member<StructT,StructN>...>>>& field){
+		{
+			auto eov = write_i<i>(vtk_file, field);
+			if(eov.is_error()){
+				return eov;
+			}
+		}
+		if constexpr ( (i+1u) < sizeof...(StructT) ){
+			return iterate_i<i+1u>(vtk_file, field);
+		}
+		return saw::make_void();
+	}
+
+	saw::error_or<void> apply(std::ofstream& vtk_file, 
+		const saw::data<CellField<Desc,Struct<Member<StructT,StructN>...>>>& field){
+		
+		auto meta = field.meta();
+		// DIMENSIONS
+		{
+			vtk_file << "DIMENSIONS ";
+			for(saw::data<sch::UInt64> i{0u}; i < Desc::D; ++i){
+				vtk_file << " " << meta.at(i).get(); 
+			}
+			for(saw::data<sch::UInt64> i{Desc::D}; i < 3u; ++i){
+				vtk_file << " 1";
+			}
+
+			vtk_file << "\n";
+		}
+
+		// HEADER TO BODY 
+		{
+			vtk_file << "\n";
+		}
+
+		if constexpr (sizeof...(StructT) > 0u){
+			return iterate_i<0u>(vtk_file, field);
+		}
+
+		return saw::make_void();
+	}
+};
+}
+
+template<typename Struct>
+saw::error_or<void> write_vtk(const std::string_view file_name, const saw::data<Struct>& field){
+
+	std::string vtk_file_name{file_name};
+	std::ofstream vtk_file{vtk_file_name};
+
+	if(!vtk_file.is_open()){
+		return saw::make_error<saw::err::critical>("Could not open file.");
+	}
+
+	vtk_file
+		<<"# vtk DataFile Version 3.0\n"
+		<<"LBM File\n"
+		<<"ASCII\n"
+		<<"DATASET STRUCTURED POINTS\n"
+		<<"SPACING 1.0 1.0 1.0\n"
+		<<"ORIGIN 0.0 0.0 0.0\n"
+	;
+
+
+	auto eov = lbm_vtk_writer::apply(vtk_file, field);
+	return eov;
+	/*
+	vtk_file <<"# vtk DataFile Version 3.0\n";
+	vtk_file <<"Velocity Cavity2D example\n";
+	vtk_file <<"ASCII\n";
+	vtk_file <<"DATASET STRUCTURED_POINTS\n";
+	vtk_file <<"DIMENSIONS "<< dim_x <<" "<<dim_y<<" 1\n";
+	vtk_file <<"SPACING 1.0 1.0 1.0\n";
+	vtk_file <<"ORIGIN 0.0 0.0 0.0\n";
+	vtk_file <<"POINT_DATA "<<(dim_x*dim_y)<<"\n";
+	vtk_file <<"VECTORS Velocity float\n";
+	*/
+:w
+}
+}
+}
-- 
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