From 4a291705f46086d5adcf68de6d6d1441c4b9e4f9 Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Thu, 8 May 2025 14:37:06 +0200
Subject: Built a working vtk file writer. Would prefer a lambda writer tbh

---
 c++/macroscopic.hpp | 31 +++++++++++++++++-
 c++/write_vtk.hpp   | 92 ++++++++++++++++++++++++++++++++++++-----------------
 2 files changed, 92 insertions(+), 31 deletions(-)

(limited to 'c++')

diff --git a/c++/macroscopic.hpp b/c++/macroscopic.hpp
index 43c727b..e126bbe 100644
--- a/c++/macroscopic.hpp
+++ b/c++/macroscopic.hpp
@@ -9,7 +9,7 @@ namespace lbm {
  */
 template<typename T, typename Desc>
 void compute_rho_u (
-		saw::data<sch::Cell<T, Desc, 0, 0, 1>>& dfs,
+		const saw::data<sch::Cell<T, Desc, 0, 0, 1>>& dfs,
 		typename saw::native_data_type<T>::type& rho,
 		std::array<typename saw::native_data_type<T>::type, 2>& vel
 	)
@@ -30,5 +30,34 @@ void compute_rho_u (
 		vel[i] /= rho;
 	}
 }
+
+/**
+ * Calculate the macroscopic variables rho and u in Lattice Units.
+ */
+template<typename T, typename Desc>
+void compute_rho_u (
+		const saw::data<sch::Cell<T, Desc, 0, 0, 1>>& dfs,
+		saw::ref<saw::data<T>> rho,
+		saw::ref<saw::data<sch::FixedArray<T,Desc::D>>> vel
+	)
+{
+	using dfi = df_info<T, Desc>;
+
+	rho().set(0);
+	for(uint64_t i = 0; i < Desc::D; ++i){
+		vel().at({i}).set(0);
+	}
+
+	for(size_t j = 0; j < Desc::Q; ++j){
+		rho = rho + dfs(j);
+		for(size_t i = 0; i < Desc::D; ++i){
+			vel[i] = vel[i] + saw::data<T>{dfi::directions[j][i]} * dfs(j);
+		}
+	}
+
+	for(size_t i = 0; i < Desc::D; ++i){
+		vel[i] = vel[i] / rho;
+	}
+}
 }
 }
diff --git a/c++/write_vtk.hpp b/c++/write_vtk.hpp
index 294ec6d..5cbc6c0 100644
--- a/c++/write_vtk.hpp
+++ b/c++/write_vtk.hpp
@@ -16,59 +16,91 @@ template<typename CellFieldSchema>
 struct lbm_vtk_writer {
 };
 
-template<typename... MemberTypes, saw::string_literal... MemberNames>
-struct lbm_vtk_writer<sch::Struct<sch::Member<MemberTypes,MemberNames>...>> {
-
-	static saw::error_or<void> apply(){
+template<typename T, uint64_t D>
+struct lbm_vtk_writer<sch::Primitive<T,D>> {
+	static saw::error_or<void> apply_header(std::ostream& vtk_file, std::string_view name){
+		vtk_file<<"SCALARS "<<name<<" float\n";
+		vtk_file<<"LOOKUP_TABLE default\n";
+		return saw::make_void();
+	}
+	static saw::error_or<void> apply(std::ostream& vtk_file, const saw::data<sch::Primitive<T,D>>& field){
+		vtk_file<<field.get()<<"\n";
 		return saw::make_void();
 	}
 };
 
 template<typename T, uint64_t D>
 struct lbm_vtk_writer<sch::FixedArray<T,D>> {
-	static saw::error_or<void> apply(std::ostream& vtk_file, std::string_view name){
+	static saw::error_or<void> apply_header(std::ostream& vtk_file, std::string_view name){
 		vtk_file<<"VECTORS "<<name<<" float\n";
+		return saw::make_void();
 	}
-};
-
-template<typename Sch, typename Desc, uint64_t SC_V, uint64_t DC_V, uint64_t QC_V>
-struct lbm_vtk_writer<sch::Cell<Sch,Desc,SC_V, DC_V, QC_V>> {
-	static saw::error_or<void> apply(std::ostream& vtk_file, std::string_view name){
-		vtk_file<<"VECTORS "<<name<<" float\n";
+	static saw::error_or<void> apply(std::ostream& vtk_file, const saw::data<sch::FixedArray<T,D>>& field){
+		static_assert(D > 0, "Non-dimensionality is bad for velocity.");
+		static_assert(D <= 3, "4th dimension as well. Mostly due to vtk.");
+
+		// vtk_file<<"VECTORS "<<name<<" float\n";
+		for(uint64_t i = 0u; i < D; ++i){
+			if(i > 0){
+				vtk_file<<" ";
+			}
+			vtk_file<<field.at({i}).get();
+		}
+		for(uint64_t i = D; i < 3; ++i){
+			vtk_file<<" 0";
+		}
+		vtk_file<<"\n";
 		return saw::make_void();
 	}
 };
 
-template<typename Desc, typename... StructT, saw::string_literal... StructN>
-struct lbm_vtk_writer<sch::CellField<Desc,sch::Struct<sch::Member<StructT,StructN>...>>> {
-	template<uint64_t i, uint64_t Dep>
-	static saw::error_or<void> write_i_iterate_d(std::ostream& vtk_file, const saw::data<sch::CellField<Desc,sch::Struct<sch::Member<StructT,StructN>...>>>& field, saw::data<sch::FixedArray<sch::UInt64,Desc::D>>& index){
-		if constexpr (Dep == Desc::D){
+template<uint64_t Dim, typename... StructT, saw::string_literal... StructN>
+struct lbm_vtk_writer<sch::Array<sch::Struct<sch::Member<StructT,StructN>...> , Dim>> {
 
+	template<uint64_t i, uint64_t Dep>
+	static saw::error_or<void> write_i_iterate_d(std::ostream& vtk_file, const saw::data<sch::Array<sch::Struct<sch::Member<StructT,StructN>...>,Dim>>& field, saw::data<sch::FixedArray<sch::UInt64,Dim>>& index){
+		constexpr auto Lit = saw::parameter_key_pack_type<i, StructN...>::literal;
+		using Type = typename saw::parameter_pack_type<i,StructT...>::type;
+
+		if constexpr (Dep == Dim){
+			return lbm_vtk_writer<Type>::apply(vtk_file, field.at(index).template get<Lit>());
+		} else {
+			// Dep < Dim // I hope
+			static_assert(Dep < Dim, "Don't fall into this case");
+			for(index.at({Dep}) = 0; index.at({Dep}) < field.get_dims().at({Dep}); ++index.at({Dep})){
+				auto eov = write_i_iterate_d<i,Dep+1>(vtk_file, field, index);
+				if(eov.is_error()){
+					return eov;
+				}
+			}
 		}
 		return saw::make_void();
 	}
 
 	template<uint64_t i>
-	static saw::error_or<void> write_i(std::ostream& vtk_file, const saw::data<sch::CellField<Desc,sch::Struct<sch::Member<StructT,StructN>...>>>& field){
+	static saw::error_or<void> write_i(std::ostream& vtk_file, const saw::data<sch::Array<sch::Struct<sch::Member<StructT,StructN>...>,Dim>>& field){
 
-		auto meta = field.meta();
-		saw::data<sch::FixedArray<sch::UInt64,Desc::D>> index;
-		for(saw::data<sch::UInt64> it{0}; it.get() < Desc::D; ++it){
+		auto meta = field.get_dims();
+		saw::data<sch::FixedArray<sch::UInt64,Dim>> index;
+		for(saw::data<sch::UInt64> it{0}; it.get() < Dim; ++it){
 			index.at({0u}).set(0u);
 		}
 		// vtk_file write?
 		// Data header
 		{
-			auto eov = lbm_vtk_writer<typename saw::parameter_pack_type<i,StructT...>::type>::apply(vtk_file, saw::parameter_key_pack_type<i, StructN...>::literal.view());
+
+			auto eov = lbm_vtk_writer<typename saw::parameter_pack_type<i,StructT...>::type>::apply_header(vtk_file, saw::parameter_key_pack_type<i, StructN...>::literal.view());
+			if(eov.is_error()){
+				return eov;
+			}
+
 		}
 		return write_i_iterate_d<i,0u>(vtk_file, field, index);
-
-		return saw::make_void();
 	}
 
 	template<uint64_t i>
-	static saw::error_or<void> iterate_i(std::ostream& vtk_file, const saw::data<sch::CellField<Desc,sch::Struct<sch::Member<StructT,StructN>...>>>& field){
+	static saw::error_or<void> iterate_i(std::ostream& vtk_file, const saw::data<sch::Array<sch::Struct<sch::Member<StructT,StructN>...>, Dim>>& field){
+		constexpr auto Lit = saw::parameter_key_pack_type<i, StructN...>::literal;
 		{
 			auto eov = write_i<i>(vtk_file, field);
 			if(eov.is_error()){
@@ -82,28 +114,28 @@ struct lbm_vtk_writer<sch::CellField<Desc,sch::Struct<sch::Member<StructT,Struct
 	}
 
 	static saw::error_or<void> apply(std::ostream& vtk_file,
-		const saw::data<sch::CellField<Desc,sch::Struct<sch::Member<StructT,StructN>...>>>& field){
+		const saw::data<sch::Array<sch::Struct<sch::Member<StructT,StructN>...>, Dim>>& field){
 
 		vtk_file
 			<<"# vtk DataFile Version 3.0\n"
 			<<"LBM File\n"
 			<<"ASCII\n"
-			<<"DATASET STRUCTURED POINTS\n"
+			<<"DATASET STRUCTURED_POINTS\n"
 			<<"SPACING 1.0 1.0 1.0\n"
 			<<"ORIGIN 0.0 0.0 0.0\n"
 		;
 		
-		auto meta = field.meta();
+		auto meta = field.get_dims();
 		saw::data<sch::UInt64> pd_size{1u};
 		// DIMENSIONS
 
 		{
-			vtk_file << "DIMENSIONS ";
-			for(saw::data<sch::UInt64> i{0u}; i.get() < Desc::D; ++i){
+			vtk_file << "DIMENSIONS";
+			for(saw::data<sch::UInt64> i{0u}; i.get() < Dim; ++i){
 				pd_size = pd_size * meta.at(i);
 				vtk_file << " " << meta.at(i).get(); 
 			}
-			for(saw::data<sch::UInt64> i{Desc::D}; i.get() < 3u; ++i){
+			for(saw::data<sch::UInt64> i{Dim}; i.get() < 3u; ++i){
 				vtk_file << " 1";
 			}
 
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