From 22659a4a4af8be137bcd702b89f1f44cd0fe2455 Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Fri, 6 Feb 2026 20:20:05 +0100
Subject: Equilibrium boundaries

---
 examples/poiseulle_particles_2d_gpu/sim.cpp |  2 +-
 lib/core/c++/boundary.hpp                   | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/examples/poiseulle_particles_2d_gpu/sim.cpp b/examples/poiseulle_particles_2d_gpu/sim.cpp
index f9ee85b..d53a00c 100644
--- a/examples/poiseulle_particles_2d_gpu/sim.cpp
+++ b/examples/poiseulle_particles_2d_gpu/sim.cpp
@@ -121,7 +121,7 @@ saw::error_or<void> step(
 		component<T,Desc,cmpt::BounceBack,encode::Sycl<saw::encode::Native>> bb;
 		component<T,Desc,cmpt::ZouHeHorizontal<true>,encode::Sycl<saw::encode::Native>> flow_in{
 			[&](){
-				uint64_t target_t_i = 128u;
+				uint64_t target_t_i = 256u;
 				if(t_i.get() < target_t_i){
 					return 1.0 + (0.001 / target_t_i) * t_i.get();
 				}
diff --git a/lib/core/c++/boundary.hpp b/lib/core/c++/boundary.hpp
index 6d83c79..b70ffbf 100644
--- a/lib/core/c++/boundary.hpp
+++ b/lib/core/c++/boundary.hpp
@@ -11,6 +11,8 @@ struct BounceBack {};
 template<bool East>
 struct ZouHeHorizontal{};
 
+struct Equilibrium {};
+
 template<bool North>
 struct ZouHeVertical{};
 }
@@ -64,6 +66,28 @@ public:
 	}
 };
 
+template<typename FP, typename Descriptor, typename Encode>
+class component<FP, Descriptor, cmpt::Equilibrium, Encode> final {
+private:
+	saw::data<FP> density_;
+	saw::data<FP> velocity_;
+public:
+	component(
+		saw::data<FP> density__,
+		saw::Data<FP> velocity__
+	):
+		density_{density__},
+		velocity_{velocity__}
+	{}
+
+	template<typename CellFieldSchema>
+	void apply(const saw::data<CellFieldSchema, Encode>& field, const saw::data<sch::FixedArray<sch::UInt64,Descriptor::D>>& index, saw::data<sch::UInt64> time_step)const{
+		using dfi = df_info<T,Descriptor>;
+		
+		auto& dfs_old_f = (is_even) ? field.template get<"dfs_old">() : field.template get<"dfs">();
+	}
+};
+
 /**
  * This is massively hacky and expects a lot of conditions
  * Either this or mirrored along the horizontal line works
-- 
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