improve tween synchronization

stepmania/src/Actor.cpp

@@ -203,23 +203,26 @@ void Actor::EndDraw()
 
 void Actor::UpdateTweening( float fDeltaTime )
 {
-	// update tweening
-	if( m_TweenStates.empty() )
+	while( 1 )
+	{
+		if( m_TweenStates.empty() ) // nothing to do
 			return;
 
-	// we are performing a tween
+		if( fDeltaTime == 0 )	// nothing will change
+			return;
+
+		// update current tween state
 		TweenState &TS = m_TweenStates[0];	// earliest tween
 		TweenInfo  &TI = m_TweenInfo[0];	// earliest tween
 
 		if( TI.m_fTimeLeftInTween == TI.m_fTweenTime )	// we are just beginning this tween
-	{
-		// set the start position
-		m_start = m_current;
-	}
+			m_start = m_current;		// set the start position
 
-	TI.m_fTimeLeftInTween -= fDeltaTime;
+		float fSecsToSubtract = min( TI.m_fTimeLeftInTween, fDeltaTime );
+		TI.m_fTimeLeftInTween -= fSecsToSubtract;
+		fDeltaTime -= fSecsToSubtract;
 	
-	if( TI.m_fTimeLeftInTween <= 0 )	// The tweening is over.  Stop the tweening
+		if( TI.m_fTimeLeftInTween == 0 )	// Current tween is over.  Stop.
 		{
 			m_current = TS;
 			
@@ -246,6 +249,7 @@ void Actor::UpdateTweening( float fDeltaTime )
 
 			TweenState::MakeWeightedAverage( m_current, m_start, TS, fPercentAlongPath );
 		}
+	}
 }
 
 bool Actor::IsFirstUpdate()