From 39ed87570bdb2f86969d4be821c94b722dc71179 Mon Sep 17 00:00:00 2001
From: Joe Ludwig <joe@valvesoftware.com>
Date: Wed, 26 Jun 2013 15:22:04 -0700
Subject: First version of the SOurce SDK 2013

---
 mp/src/game/shared/rope_helpers.cpp | 140 ++++++++++++++++++++++++++++++++++++
 1 file changed, 140 insertions(+)
 create mode 100644 mp/src/game/shared/rope_helpers.cpp

(limited to 'mp/src/game/shared/rope_helpers.cpp')

diff --git a/mp/src/game/shared/rope_helpers.cpp b/mp/src/game/shared/rope_helpers.cpp
new file mode 100644
index 00000000..4150a74f
--- /dev/null
+++ b/mp/src/game/shared/rope_helpers.cpp
@@ -0,0 +1,140 @@
+//========= Copyright Valve Corporation, All rights reserved. ============//
+//
+// Purpose: 
+//
+// $NoKeywords: $
+//=============================================================================//
+
+#include "cbase.h"
+#include "rope_helpers.h"
+#include "basetypes.h"
+#include "mathlib/mathlib.h"
+#include "rope_shared.h"
+#include "rope_physics.h"
+#include "networkvar.h"
+
+// memdbgon must be the last include file in a .cpp file!!!
+#include "tier0/memdbgon.h"
+
+class CHangRope : public CRopePhysics<512>
+{
+DECLARE_CLASS( CHangRope, CRopePhysics<512> );
+
+// CRopePhysics overrides.
+public:
+
+	virtual void	GetNodeForces( CSimplePhysics::CNode *pNodes, int iNode, Vector *pAccel )
+	{
+		pAccel->Init( ROPE_GRAVITY );
+	}
+
+	
+	virtual void ApplyConstraints( CSimplePhysics::CNode *pNodes, int nNodes )
+	{
+		// Apply spring forces.
+		BaseClass::ApplyConstraints( pNodes, nNodes );
+
+
+		// Lock the endpoints.
+		pNodes[0].m_vPos = m_vEndPoints[0];
+		pNodes[nNodes-1].m_vPos = m_vEndPoints[1];
+
+
+		// Calculate how far it is hanging down and adjust if necessary.
+		float flCurHangDist = 0;
+		for ( int i=0; i < NumNodes(); i++ )
+		{
+			float hang = fabs( m_flStartZ - GetNode(i)->m_vPos.z );
+			if ( hang > flCurHangDist )
+				flCurHangDist = hang;
+		}
+		
+		// Adjust our spring length accordingly.
+		if ( flCurHangDist < m_flWantedHangDist )
+			m_flCurSlack += 1;
+		else
+			m_flCurSlack -= 1;
+
+		ApplyNewSpringLength();
+	}
+
+
+// Helpers.
+public:
+	
+	void	ApplyNewSpringLength()
+	{
+		ResetSpringLength( (m_flRopeLength + m_flCurSlack + ROPESLACK_FUDGEFACTOR) / (NumNodes() - 1) );
+	}
+
+
+// Variables used to adjust the rope slack.
+public:
+
+	Vector	m_vEndPoints[2];
+	bool	m_bAdjustSlack;
+	
+	float	m_flRopeLength;
+	float	m_flCurSlack;
+
+	float	m_flWantedHangDist;
+	float	m_flStartZ;
+
+};
+
+
+
+void CalcRopeStartingConditions( 
+	const Vector &vStartPos,
+	const Vector &vEndPos,
+	int const nNodes,
+	float const desiredHang,
+	float *pOutputLength,
+	float *pOutputSlack
+	)
+{
+	CHangRope rope;
+
+	// Initialize the rope as a straight line with no slack as our first approximation.
+	// We then relax the rope by adding slack until it hangs to the desired height.
+	//	
+	// The spring length equation is:
+	// springLength = (ropeLength + slack + ROPESLACK_FUDGEFACTOR) / (nNodes - 1)
+	//
+	// We want our rope to be a straight line, so: 
+	// springLength = ropeLength / (nNodes-1)
+	//
+	// Therefore our initial slack is -ROPESLACK_FUDGEFACTOR
+	rope.m_flCurSlack = -ROPESLACK_FUDGEFACTOR;
+
+	rope.m_vEndPoints[0] = vStartPos;
+	rope.m_vEndPoints[1] = vEndPos;
+	
+	rope.m_flRopeLength = (vEndPos - vStartPos).Length();
+	rope.m_flWantedHangDist = desiredHang;
+	
+	rope.m_flStartZ = MIN( vStartPos.z, vEndPos.z );	// Calculate hang as the Z distance from the
+														// lowest endpoint to the bottom of the rope.
+	
+	rope.SetNumNodes( nNodes );
+
+	// Set the node positions.
+	for ( int i=0; i < rope.NumNodes(); i++ )
+	{
+		CSimplePhysics::CNode *pNode = rope.GetNode( i );
+
+		float t = (float)i / (rope.NumNodes() - 1);
+		VectorLerp( vStartPos, vEndPos, t, pNode->m_vPos );
+		pNode->m_vPrevPos = pNode->m_vPos;
+	}
+
+	// Now simulate a little and stretch out to let it hang down.
+	rope.Restart();
+	rope.Simulate( 3 );
+
+	// Set outputs.
+	*pOutputLength = rope.m_flRopeLength;
+	*pOutputSlack = rope.m_flCurSlack;
+}
+
+
-- 
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