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diff --git a/public/simple_physics.h b/public/simple_physics.h
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+//========= Copyright Valve Corporation, All rights reserved. ============//
+//
+// Purpose: 
+//
+// $NoKeywords: $
+//=============================================================================//
+
+#ifndef SIMPLE_PHYSICS_H
+#define SIMPLE_PHYSICS_H
+#ifdef _WIN32
+#pragma once
+#endif
+
+
+#include "mathlib/vector.h"
+
+
+// CSimplePhysics is a framework for simplified physics simulation.
+// It simulates at a fixed timestep and uses the Verlet integrator.
+//
+// To use it, create your nodes and implement your constraints and
+// forces in an IHelper, then call Simulate each frame. 
+// CSimplePhysics will figure out how many timesteps to run and will
+// provide predicted positions of things for you.
+class CSimplePhysics
+{
+public:
+
+	class CNode
+	{
+	public:
+		
+		// Call this when initializing the nodes with their starting positions.
+		void		Init( const Vector &vPos )
+		{
+			m_vPos = m_vPrevPos = m_vPredicted = vPos;
+		}
+		
+		Vector		m_vPos;			// At time t
+		Vector		m_vPrevPos;		// At time t - m_flTimeStep
+		Vector		m_vPredicted;	// Predicted position
+	};
+
+	class IHelper
+	{
+	public:
+		virtual void	GetNodeForces( CNode *pNodes, int iNode, Vector *pAccel ) = 0;
+		virtual void	ApplyConstraints( CNode *pNodes, int nNodes ) = 0;
+	};
+
+
+public:
+
+				CSimplePhysics();
+	
+	void		Init( float flTimeStep );
+	
+	void		Simulate( 
+		CNode *pNodes, 
+		int nNodes, 
+		IHelper *pHelper, 
+		float dt,
+		float flDamp );
+
+
+private:
+
+	double		GetCurTime()		{ return m_flTimeStep * m_iCurTimeStep; }
+
+
+private:
+
+	double		m_flPredictedTime;	// (GetCurTime()-m_flTimeStep) <= m_flPredictedTime <= GetCurTime()
+	int			m_iCurTimeStep;
+	
+	float		m_flTimeStep;
+	float		m_flTimeStepMul;	// dt*dt*0.5
+};
+
+ 
+#endif // SIMPLE_PHYSICS_H