From 75fda9a23cd30efa72bd212d5642c3d30ee34913 Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Tue, 3 Mar 2026 19:03:05 +0100
Subject: Added CSV for simpler script processing

---
 examples/poiseulle_particles_2d_gpu/sim.cpp |  42 +++++--
 lib/core/c++/lbm.hpp                        |   1 +
 lib/core/c++/write_csv.hpp                  | 184 ++++++++++++++++++++++++++++
 3 files changed, 217 insertions(+), 10 deletions(-)
 create mode 100644 lib/core/c++/write_csv.hpp

diff --git a/examples/poiseulle_particles_2d_gpu/sim.cpp b/examples/poiseulle_particles_2d_gpu/sim.cpp
index e7aec8e..6d012e0 100644
--- a/examples/poiseulle_particles_2d_gpu/sim.cpp
+++ b/examples/poiseulle_particles_2d_gpu/sim.cpp
@@ -337,6 +337,12 @@ saw::error_or<void> lbm_main(int argc, char** argv){
 			return eov;
 		}
 	}
+	{
+		auto eov = write_vtk_file(out_dir,"initial_state",0u,*lbm_data_ptr);
+		if(eov.is_error()){
+			return eov;
+		}
+	}
 
 	saw::data<sch::ChunkStruct<T,Desc>, encode::Sycl<saw::encode::Native>> lbm_sycl_data{sycl_q};
 	saw::data<sch::MacroStruct<T,Desc>, encode::Sycl<saw::encode::Native>> lbm_sycl_macro_data{sycl_q};
@@ -364,9 +370,9 @@ saw::error_or<void> lbm_main(int argc, char** argv){
 		}
 	}
 	sycl_q.wait();
-	saw::data<sch::UInt64> time_steps{128ul};
+	saw::data<sch::UInt64> time_steps{32ul};
 
-	auto& info_f = lbm_sycl_data.template get<"info">();
+	auto& info_f = lsd_view.template get<"info">();
 
 	for(saw::data<sch::UInt64> i{0u}; i < time_steps and krun; ++i){
 		// BC + Collision
@@ -378,15 +384,31 @@ saw::error_or<void> lbm_main(int argc, char** argv){
 		}
 		sycl_q.wait();
 		{
-			auto eov = dev.copy_to_host(lbm_sycl_macro_data,*lbm_macro_data_ptr);
-			if(eov.is_error()){
-				return eov;
+			{
+				auto eov = dev.copy_to_host(lbm_sycl_macro_data,*lbm_macro_data_ptr);
+				if(eov.is_error()){
+					return eov;
+				}
+			}
+			{
+				auto eov = write_vtk_file(out_dir,"m",i.get(), *lbm_macro_data_ptr);
+				if(eov.is_error()){
+					return eov;
+				}
 			}
 		}
 		{
-			auto eov = write_vtk_file(out_dir,"t",time_steps.get(), *lbm_macro_data_ptr);
-			if(eov.is_error()){
-				return eov;
+			{
+				auto eov = dev.copy_to_host(lbm_sycl_data,*lbm_data_ptr);
+				if(eov.is_error()){
+					return eov;
+				}
+			}
+			{
+				auto eov = write_csv_file(out_dir,"lbm",i.get(), *lbm_data_ptr);
+				if(eov.is_error()){
+					return eov;
+				}
 			}
 		}
 		// Stream
@@ -402,7 +424,7 @@ saw::error_or<void> lbm_main(int argc, char** argv){
 				auto info = info_f.at(index);
 				
 				if(info.get() > 0u){
-					stream.apply(fields,index,t_i);
+					stream.apply(lsd_view,index,i);
 				}
 			});
 		}).wait();
@@ -416,7 +438,7 @@ saw::error_or<void> lbm_main(int argc, char** argv){
 	// After Loop
 	sycl_q.wait();
 	{
-		auto eov = write_vtk_file(out_dir,"t",time_steps.get(), *lbm_macro_data_ptr);
+		auto eov = write_vtk_file(out_dir,"m",time_steps.get(), *lbm_macro_data_ptr);
 		if(eov.is_error()){
 			return eov;
 		}
diff --git a/lib/core/c++/lbm.hpp b/lib/core/c++/lbm.hpp
index a1e088e..d6a0976 100644
--- a/lib/core/c++/lbm.hpp
+++ b/lib/core/c++/lbm.hpp
@@ -17,6 +17,7 @@
 #include "memory.hpp"
 #include "psm.hpp"
 #include "stream.hpp"
+#include "write_csv.hpp"
 #include "write_vtk.hpp"
 #include "util.hpp"
 
diff --git a/lib/core/c++/write_csv.hpp b/lib/core/c++/write_csv.hpp
new file mode 100644
index 0000000..a60e208
--- /dev/null
+++ b/lib/core/c++/write_csv.hpp
@@ -0,0 +1,184 @@
+#pragma once
+
+#include <forstio/error.hpp>
+
+#include <forstio/codec/data.hpp>
+#include <forstio/codec/data_math.hpp>
+
+#include "descriptor.hpp"
+#include "flatten.hpp"
+#include "chunk.hpp"
+
+#include <fstream>
+#include <filesystem>
+
+namespace kel {
+namespace lbm {
+namespace impl {
+
+template<typename CellFieldSchema>
+struct lbm_csv_writer {
+};
+
+template<typename T, uint64_t D>
+struct lbm_csv_writer<sch::Primitive<T,D>> {
+	static saw::error_or<void> apply(std::ostream& csv_file, const saw::data<sch::Primitive<T,D>>& field){
+		if constexpr (std::is_same_v<T,sch::UnsignedInteger> and D == 1u) {
+			csv_file<<field.template cast_to<sch::UInt16>().get();
+		}else{
+			csv_file<<field.get();
+		}
+		return saw::make_void();
+	}
+};
+
+template<typename T, uint64_t D>
+struct lbm_csv_writer<sch::FixedArray<T,D>> {
+	static saw::error_or<void> apply(std::ostream& csv_file, const saw::data<sch::FixedArray<T,D>>& field){
+		saw::data<sch::FixedArray<sch::UInt64,D>> index;
+		for(saw::data<sch::UInt64> it{0}; it.get() < D; ++it){
+			index.at({0u}).set(0u);
+		}
+
+		// csv_file<<"VECTORS "<<name<<" float\n";
+		for(uint64_t i = 0u; i < D; ++i){
+			if(i > 0){
+				csv_file<<",";
+			}
+			csv_file<<field.at({i}).get();
+		}
+		return saw::make_void();
+	}
+};
+
+template<typename T, uint64_t Ghost, uint64_t... D>
+struct lbm_csv_writer<sch::Chunk<T,Ghost,D...>> {
+
+	template<uint64_t d>
+	static saw::error_or<void> apply_d(std::ostream& csv_file, const saw::data<sch::Chunk<T,Ghost,D...>>& field, saw::data<sch::FixedArray<sch::UInt64,sizeof...(D)>>& index){
+		// VTK wants to iterate over z,y,x instead of x,y,z
+		// So we do the same with CSV to stay consistent for now
+		// We could reorder the dimensions, but eh
+		if constexpr ( d > 0u){
+			for(index.at({d-1u}) = 0u; index.at({d-1u}) < field.get_dims().at({d-1u}); ++index.at({d-1u})){
+				auto eov = apply_d<d-1u>(csv_file, field, index);
+			}
+		}else{
+			auto eov = lbm_csv_writer<T>::apply(csv_file, field.at(index));
+			csv_file<<"\n";
+			if(eov.is_error()) return eov;
+		}
+		return saw::make_void();
+	}
+
+	static saw::error_or<void> apply(std::ostream& csv_file, const saw::data<sch::Chunk<T,Ghost,D...>>& field, std::string_view name){
+		saw::data<sch::FixedArray<sch::UInt64,sizeof...(D)>> index;
+		for(saw::data<sch::UInt64> it{0}; it.get() < sizeof...(D); ++it){
+			index.at({0u}).set(0u);
+		}
+
+		{
+			auto eov = apply_d<sizeof...(D)>(csv_file, field, index);
+			if(eov.is_error()){
+				return eov;
+			}
+		}
+
+		return saw::make_void();
+	}
+};
+
+template<typename T, uint64_t D>
+struct lbm_csv_writer<sch::Vector<T,D>> {
+	static saw::error_or<void> apply(std::ostream& csv_file, const saw::data<sch::Vector<T,D>>& field){
+		static_assert(D > 0, "Non-dimensionality is bad for velocity.");
+
+		// csv_file<<"VECTORS "<<name<<" float\n";
+		for(uint64_t i = 0u; i < D; ++i){
+			if(i > 0){
+				csv_file<<",";
+			}
+			{
+				auto eov = lbm_csv_writer<T>::apply(csv_file,field.at({{i}}));
+				if(eov.is_error()) return eov;
+			}
+		}
+		return saw::make_void();
+	}
+};
+
+template<typename T>
+struct lbm_csv_writer<sch::Scalar<T>> {
+	static saw::error_or<void> apply(std::ostream& csv_file, const saw::data<sch::Scalar<T>>& field){
+		return lbm_csv_writer<T>::apply(csv_file,field.at({}));
+	}
+};
+
+template<typename... MemberT, saw::string_literal... Keys, uint64_t... Ghost, uint64_t... Dims>
+struct lbm_csv_writer<sch::Struct<sch::Member<sch::Chunk<MemberT,Ghost,Dims...>,Keys>...>> final  {
+	template<uint64_t i>
+	static saw::error_or<void> iterate_i(
+			const std::filesystem::path& csv_dir, const std::string_view& file_base_name, uint64_t d_t, 
+			const saw::data<sch::Struct<sch::Member<sch::Chunk<MemberT,Ghost,Dims...>,Keys>...>>& field){
+
+		if constexpr ( i < sizeof...(MemberT) ) {
+			using MT = typename saw::parameter_pack_type<i,sch::Member<sch::Chunk<MemberT,Ghost,Dims...>,Keys>...>::type;
+			{
+				std::stringstream sstr;
+				sstr
+					<<file_base_name
+					<<"_"
+					<<MT::Key.view()
+					<<"_"
+					<<d_t
+					<<".csv"
+				;
+				std::ofstream csv_file{csv_dir / sstr.str() };
+
+				if( not csv_file.is_open() ){
+					return saw::make_error<saw::err::critical>("Could not open file.");
+				}
+				// 
+				auto eov = lbm_csv_writer<typename MT::ValueType>::apply(csv_file,field.template get<MT::KeyLiteral>(), MT::KeyLiteral.view());
+				if(eov.is_error()){
+					return eov;
+				}
+			}
+
+			return iterate_i<i+1u>(csv_dir, file_base_name, d_t,field);
+		}
+
+		return saw::make_void();
+	}
+
+
+	static saw::error_or<void> apply(
+			const std::filesystem::path& csv_dir, const std::string_view& file_base_name, uint64_t d_t, 
+			const saw::data<sch::Struct<sch::Member<sch::Chunk<MemberT,Ghost,Dims...>,Keys>...>>& field){
+		
+		auto& field_0 = field.template get<saw::parameter_key_pack_type<0u,Keys...>::literal>();	
+		auto meta = field_0.get_dims();
+		
+		return iterate_i<0u>(csv_dir,file_base_name, d_t, field);
+	}
+};
+
+}
+
+template<typename Sch>
+saw::error_or<void> write_csv_file(const std::filesystem::path& out_dir, const std::string_view& file_name, uint64_t d_t, const saw::data<Sch>& field){
+
+	auto csv_dir = out_dir / "csv";
+	{
+		std::error_code ec;
+		std::filesystem::create_directories(csv_dir,ec);
+		if(ec != std::errc{}){
+			return saw::make_error<saw::err::critical>("Could not create directory for write_csv_file function");
+		}
+	}
+	auto eov = impl::lbm_csv_writer<Sch>::apply(csv_dir, file_name, d_t, field);
+	return eov;
+}
+
+}
+}
-- 
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