networking

external/steamworks/steamworksexample/SpaceWarEntity.cpp

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+//========= Copyright © 1996-2008, Valve LLC, All rights reserved. ============
+//
+// Purpose: A SpaceWarEntity is just like a VectorEntity, except it knows how
+//			to apply gravity from the SpaceWar Sun
+//
+// $NoKeywords: $
+//=============================================================================
+
+#include "stdafx.h"
+#include "SpaceWarEntity.h"
+#include "stdlib.h"
+#include <math.h>
+
+//-----------------------------------------------------------------------------
+// Purpose: Constructor
+//-----------------------------------------------------------------------------
+CSpaceWarEntity::CSpaceWarEntity( IGameEngine *pGameEngine, uint32 uCollisionRadius, bool bAffectedByGravity ) 
+	: CVectorEntity( pGameEngine, uCollisionRadius )
+{
+	m_bAffectedByGravity = bAffectedByGravity;
+}
+
+//-----------------------------------------------------------------------------
+// Purpose: RunFrame
+//-----------------------------------------------------------------------------
+void CSpaceWarEntity::RunFrame()
+{
+
+	if ( m_bAffectedByGravity )
+	{
+		float xAccel = GetXAcceleration();
+		float yAccel = GetYAcceleration();
+
+		// Ships are also affected by the suns gravity, compute that here, sun is always at the center of the screen
+		float xPosSun = (float)m_pGameEngine->GetViewportWidth()/2;
+		float yPosSun = (float)m_pGameEngine->GetViewportHeight()/2;
+
+		float distanceToSun = (float)sqrt( pow( xPosSun - GetXPos(), 2 ) + pow( yPosSun - GetYPos(), 2 ) );
+		float distancePower = (float)pow( distanceToSun, 2.0f ); // gravity power falls off exponentially
+		float factor = MIN( 5200000.0f / distancePower, 150.0f ); // arbitrary value for power of gravity
+
+		float xDirection = (GetXPos() - xPosSun)/distanceToSun;
+		float yDirection = (GetYPos() - yPosSun)/distanceToSun;
+
+		xAccel -= factor * xDirection;
+		yAccel -= factor * yDirection;
+
+		// Set updated acceleration
+		SetAcceleration( xAccel, yAccel );
+	}
+
+	CVectorEntity::RunFrame();
+}