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/public/rope_physics.cpp | 152 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 152 insertions(+)
 create mode 100644 mp/src/public/rope_physics.cpp

(limited to 'mp/src/public/rope_physics.cpp')

diff --git a/mp/src/public/rope_physics.cpp b/mp/src/public/rope_physics.cpp
new file mode 100644
index 00000000..fb4204a0
--- /dev/null
+++ b/mp/src/public/rope_physics.cpp
@@ -0,0 +1,152 @@
+//========= Copyright Valve Corporation, All rights reserved. ============//
+//
+// Purpose: 
+//
+// $NoKeywords: $
+//
+//=============================================================================//
+
+
+#include "rope_physics.h"
+#include "tier0/dbg.h"
+
+// memdbgon must be the last include file in a .cpp file!!!
+#include "tier0/memdbgon.h"
+
+CBaseRopePhysics::CBaseRopePhysics( CSimplePhysics::CNode *pNodes, int nNodes, CRopeSpring *pSprings, float *flSpringDistsSqr )
+{
+	m_pNodes = pNodes;
+	m_pSprings = pSprings;
+	m_flNodeSpringDistsSqr = flSpringDistsSqr;
+	m_flSpringDist = m_flSpringDistSqr = 1;
+	Restart();
+
+	// Initialize the nodes.
+	for ( int i=0; i < nNodes; i++ )
+	{
+		pNodes[i].m_vPos.Init();
+		pNodes[i].m_vPrevPos.Init();
+		pNodes[i].m_vPredicted.Init();
+	}
+
+	SetNumNodes( nNodes );
+
+	m_pDelegate = NULL;
+}
+
+
+void CBaseRopePhysics::SetNumNodes( int nNodes )
+{
+	m_nNodes = nNodes;
+
+	// Setup the springs.
+	for( int i=0; i < NumSprings(); i++ )
+	{
+		m_pSprings[i].m_pNode1 = &m_pNodes[i].m_vPos;
+		m_pSprings[i].m_pNode2 = &m_pNodes[i+1].m_vPos;
+		Assert( m_pSprings[i].m_pNode1->IsValid() ); 
+		Assert( m_pSprings[i].m_pNode2->IsValid() ); 
+
+		m_flNodeSpringDistsSqr[i] = m_flSpringDistSqr / NumSprings();
+	}
+}
+
+
+void CBaseRopePhysics::Restart()
+{
+	m_Physics.Init( 1.0 / 50 );
+}
+
+
+void CBaseRopePhysics::ResetSpringLength( float flSpringDist )
+{
+	m_flSpringDist = max( flSpringDist, 0 );
+	m_flSpringDistSqr = m_flSpringDist * m_flSpringDist;
+
+	for( int i=0; i < NumSprings(); i++ )
+	{
+		m_flNodeSpringDistsSqr[i] = m_flSpringDistSqr / NumSprings();
+	}
+}
+
+float CBaseRopePhysics::GetSpringLength() const
+{
+	return m_flSpringDist;
+}
+
+void CBaseRopePhysics::ResetNodeSpringLength( int iStartNode, float flSpringDist )
+{
+	m_flNodeSpringDistsSqr[iStartNode] = flSpringDist * flSpringDist;
+}
+
+void CBaseRopePhysics::SetupSimulation( float flSpringDist, CSimplePhysics::IHelper *pDelegate )
+{
+	ResetSpringLength( flSpringDist );
+	SetDelegate( pDelegate );
+}
+
+
+void CBaseRopePhysics::SetDelegate( CSimplePhysics::IHelper *pDelegate )
+{
+	m_pDelegate = pDelegate;
+}
+
+
+void CBaseRopePhysics::Simulate( float dt )
+{
+	static float flEnergy = 0.98;
+	m_Physics.Simulate( m_pNodes, m_nNodes, this, dt, flEnergy );
+}
+
+
+void CBaseRopePhysics::GetNodeForces( CSimplePhysics::CNode *pNodes, int iNode, Vector *pAccel )
+{
+	if( m_pDelegate )
+		m_pDelegate->GetNodeForces( pNodes, iNode, pAccel );
+	else
+		pAccel->Init( 0, 0, 0 );
+}
+
+
+void CBaseRopePhysics::ApplyConstraints( CSimplePhysics::CNode *pNodes, int nNodes )
+{
+	// Handle springs..
+	//
+	// Iterate multiple times here. If we don't, then gravity tends to
+	// win over the constraint solver and it's impossible to get straight ropes.
+	static int nIterations = 3;
+	for( int iIteration=0; iIteration < nIterations; iIteration++ )
+	{
+		for( int i=0; i < NumSprings(); i++ )
+		{
+			CRopeSpring *s = &m_pSprings[i];
+
+			Vector vTo = *s->m_pNode1 - *s->m_pNode2;
+
+			float flDistSqr = vTo.LengthSqr();
+
+			// If we don't have an overall spring distance, see if we have a per-node one
+			float flSpringDist = m_flSpringDistSqr;
+			if ( !flSpringDist )
+			{
+				// TODO: This still isn't enough. Ropes with different spring lengths
+				// per-node will oscillate forever.
+				flSpringDist = m_flNodeSpringDistsSqr[i];
+			}
+
+			if( flDistSqr > flSpringDist )
+			{
+				float flDist = (float)sqrt( flDistSqr );
+				vTo *= 1 - (m_flSpringDist / flDist);
+
+				*s->m_pNode1 -= vTo * 0.5f;
+				*s->m_pNode2 += vTo * 0.5f;
+			}
+		}
+
+		if( m_pDelegate )
+			m_pDelegate->ApplyConstraints( pNodes, nNodes );
+	}
+}
+
+
-- 
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