SDK: Add components and system for 2D physics

SDK/include/NDK/Systems/PhysicsSystem2D.hpp

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+// Copyright (C) 2015 Jérôme Leclercq
+// This file is part of the "Nazara Development Kit"
+// For conditions of distribution and use, see copyright notice in Prerequesites.hpp
+
+#pragma once
+
+#ifndef NDK_SYSTEMS_PHYSICSSYSTEM2D_HPP
+#define NDK_SYSTEMS_PHYSICSSYSTEM2D_HPP
+
+#include <Nazara/Physics2D/PhysWorld2D.hpp>
+#include <NDK/EntityList.hpp>
+#include <NDK/System.hpp>
+#include <memory>
+
+namespace Ndk
+{
+	class NDK_API PhysicsSystem2D : public System<PhysicsSystem2D>
+	{
+		public:
+			PhysicsSystem2D();
+			PhysicsSystem2D(const PhysicsSystem2D& system);
+			~PhysicsSystem2D() = default;
+
+			Nz::PhysWorld2D& GetWorld();
+			const Nz::PhysWorld2D& GetWorld() const;
+
+			static SystemIndex systemIndex;
+
+		private:
+			void CreatePhysWorld() const;
+			void OnEntityValidation(Entity* entity, bool justAdded) override;
+			void OnUpdate(float elapsedTime) override;
+
+			EntityList m_dynamicObjects;
+			EntityList m_staticObjects;
+			mutable std::unique_ptr<Nz::PhysWorld2D> m_world; ///TODO: std::optional (Should I make a Nz::Optional class?)
+	};
+}
+
+#include <NDK/Systems/PhysicsSystem2D.inl>
+
+#endif // NDK_SYSTEMS_PHYSICSSYSTEM2D_HPP