void CLagCompensationManager::BacktrackPlayer( CBasePlayer *pPlayer, float flTargetTime )
{
	Vector org;
	Vector minsPreScaled;
	Vector maxsPreScaled;
	QAngle ang;

	VPROF_BUDGET( "BacktrackPlayer", "CLagCompensationManager" );
	int pl_index = pPlayer->entindex() - 1;

	// get track history of this player
	CUtlFixedLinkedList< LagRecord > *track = &m_PlayerTrack[ pl_index ];

	// check if we have at leat one entry
	if ( track->Count() <= 0 )
		return;

	int curr = track->Head();

	LagRecord *prevRecord = NULL;
	LagRecord *record = NULL;

	Vector prevOrg = pPlayer->GetLocalOrigin();
	
	// Walk context looking for any invalidating event
	while( track->IsValidIndex(curr) )
	{
		// remember last record
		prevRecord = record;

		// get next record
		record = &track->Element( curr );

		if ( !(record->m_fFlags & LC_ALIVE) )
		{
			// player most be alive, lost track
			return;
		}

		Vector delta = record->m_vecOrigin - prevOrg;
		if ( delta.Length2DSqr() > m_flTeleportDistanceSqr )
		{
			// lost track, too much difference
			return; 
		}

		// did we find a context smaller than target time ?
		if ( record->m_flSimulationTime <= flTargetTime )
			break; // hurra, stop

		prevOrg = record->m_vecOrigin;

		// go one step back
		curr = track->Next( curr );
	}

	Assert( record );

	if ( !record )
	{
		if ( sv_unlag_debug.GetBool() )
		{
			DevMsg( "No valid positions in history for BacktrackPlayer client ( %s )\n", pPlayer->GetPlayerName() );
		}

		return; // that should never happen
	}

	float frac = 0.0f;
	if ( prevRecord && 
		 (record->m_flSimulationTime < flTargetTime) &&
		 (record->m_flSimulationTime < prevRecord->m_flSimulationTime) )
	{
		// we didn't find the exact time but have a valid previous record
		// so interpolate between these two records;

		Assert( prevRecord->m_flSimulationTime > record->m_flSimulationTime );
		Assert( flTargetTime < prevRecord->m_flSimulationTime );

		// calc fraction between both records
		frac = ( flTargetTime - record->m_flSimulationTime ) / 
			( prevRecord->m_flSimulationTime - record->m_flSimulationTime );

		Assert( frac > 0 && frac < 1 ); // should never extrapolate

		ang				= Lerp( frac, record->m_vecAngles, prevRecord->m_vecAngles );
		org				= Lerp( frac, record->m_vecOrigin, prevRecord->m_vecOrigin );
		minsPreScaled	= Lerp( frac, record->m_vecMinsPreScaled, prevRecord->m_vecMinsPreScaled );
		maxsPreScaled	= Lerp( frac, record->m_vecMaxsPreScaled, prevRecord->m_vecMaxsPreScaled );
	}
	else
	{
		// we found the exact record or no other record to interpolate with
		// just copy these values since they are the best we have
		org				= record->m_vecOrigin;
		ang				= record->m_vecAngles;
		minsPreScaled	= record->m_vecMinsPreScaled;
		maxsPreScaled	= record->m_vecMaxsPreScaled;
	}

	// See if this is still a valid position for us to teleport to
	if ( sv_unlag_fixstuck.GetBool() )
	{
		// Try to move to the wanted position from our current position.
		trace_t tr;
		UTIL_TraceEntity( pPlayer, org, org, MASK_PLAYERSOLID, &tr );
		if ( tr.startsolid || tr.allsolid )
		{
			if ( sv_unlag_debug.GetBool() )
				DevMsg( "WARNING: BackupPlayer trying to back player into a bad position - client %s\n", pPlayer->GetPlayerName() );

			CBasePlayer *pHitPlayer = dynamic_cast<CBasePlayer *>( tr.m_pEnt );

			// don't lag compensate the current player
			if ( pHitPlayer && ( pHitPlayer != m_pCurrentPlayer ) )	
			{
				// If we haven't backtracked this player, do it now
				// this deliberately ignores WantsLagCompensationOnEntity.
				if ( !m_RestorePlayer.Get( pHitPlayer->entindex() - 1 ) )
				{
					// prevent recursion - save a copy of m_RestorePlayer,
					// pretend that this player is off-limits
					int pl_index = pPlayer->entindex() - 1;

					// Temp turn this flag on
					m_RestorePlayer.Set( pl_index );

					BacktrackPlayer( pHitPlayer, flTargetTime );

					// Remove the temp flag
					m_RestorePlayer.Clear( pl_index );
				}				
			}

			// now trace us back as far as we can go
			UTIL_TraceEntity( pPlayer, pPlayer->GetLocalOrigin(), org, MASK_PLAYERSOLID, &tr );

			if ( tr.startsolid || tr.allsolid )
			{
				// Our starting position is bogus

				if ( sv_unlag_debug.GetBool() )
					DevMsg( "Backtrack failed completely, bad starting position\n" );
			}
			else
			{
				// We can get to a valid place, but not all the way to the target
				Vector vPos;
				VectorLerp( pPlayer->GetLocalOrigin(), org, tr.fraction * g_flFractionScale, vPos );
				
				// This is as close as we're going to get
				org = vPos;

				if ( sv_unlag_debug.GetBool() )
					DevMsg( "Backtrack got most of the way\n" );
			}
		}
	}
	
	// See if this represents a change for the player
	int flags = 0;
	LagRecord *restore = &m_RestoreData[ pl_index ];
	LagRecord *change  = &m_ChangeData[ pl_index ];

	QAngle angdiff = pPlayer->GetLocalAngles() - ang;
	Vector orgdiff = pPlayer->GetLocalOrigin() - org;

	// Always remember the pristine simulation time in case we need to restore it.
	restore->m_flSimulationTime = pPlayer->GetSimulationTime();

	if ( angdiff.LengthSqr() > LAG_COMPENSATION_EPS_SQR )
	{
		flags |= LC_ANGLES_CHANGED;
		restore->m_vecAngles = pPlayer->GetLocalAngles();
		pPlayer->SetLocalAngles( ang );
		change->m_vecAngles = ang;
	}

	// Use absolute equality here
	if ( minsPreScaled != pPlayer->CollisionProp()->OBBMinsPreScaled() || maxsPreScaled != pPlayer->CollisionProp()->OBBMaxsPreScaled() )
	{
		flags |= LC_SIZE_CHANGED;

		restore->m_vecMinsPreScaled = pPlayer->CollisionProp()->OBBMinsPreScaled();
		restore->m_vecMaxsPreScaled = pPlayer->CollisionProp()->OBBMaxsPreScaled();
		
		pPlayer->SetSize( minsPreScaled, maxsPreScaled );
		
		change->m_vecMinsPreScaled = minsPreScaled;
		change->m_vecMaxsPreScaled = maxsPreScaled;
	}

	// Note, do origin at end since it causes a relink into the k/d tree
	if ( orgdiff.LengthSqr() > LAG_COMPENSATION_EPS_SQR )
	{
		flags |= LC_ORIGIN_CHANGED;
		restore->m_vecOrigin = pPlayer->GetLocalOrigin();
		pPlayer->SetLocalOrigin( org );
		change->m_vecOrigin = org;
	}

	// Sorry for the loss of the optimization for the case of people
	// standing still, but you breathe even on the server.
	// This is quicker than actually comparing all bazillion floats.
	flags |= LC_ANIMATION_CHANGED;
	restore->m_masterSequence = pPlayer->GetSequence();
	restore->m_masterCycle = pPlayer->GetCycle();

	bool interpolationAllowed = false;
	if( prevRecord && (record->m_masterSequence == prevRecord->m_masterSequence) )
	{
		// If the master state changes, all layers will be invalid too, so don't interp (ya know, interp barely ever happens anyway)
		interpolationAllowed = true;
	}
	
	////////////////////////
	// First do the master settings
	bool interpolatedMasters = false;
	if( frac > 0.0f && interpolationAllowed )
	{
		interpolatedMasters = true;
		pPlayer->SetSequence( Lerp( frac, record->m_masterSequence, prevRecord->m_masterSequence ) );
		pPlayer->SetCycle( Lerp( frac, record->m_masterCycle, prevRecord->m_masterCycle ) );

		if( record->m_masterCycle > prevRecord->m_masterCycle )
		{
			// the older record is higher in frame than the newer, it must have wrapped around from 1 back to 0
			// add one to the newer so it is lerping from .9 to 1.1 instead of .9 to .1, for example.
			float newCycle = Lerp( frac, record->m_masterCycle, prevRecord->m_masterCycle + 1 );
			pPlayer->SetCycle(newCycle < 1 ? newCycle : newCycle - 1 );// and make sure .9 to 1.2 does not end up 1.05
		}
		else
		{
			pPlayer->SetCycle( Lerp( frac, record->m_masterCycle, prevRecord->m_masterCycle ) );
		}
	}
	if( !interpolatedMasters )
	{
		pPlayer->SetSequence(record->m_masterSequence);
		pPlayer->SetCycle(record->m_masterCycle);
	}

	////////////////////////
	// Now do all the layers
	int layerCount = pPlayer->GetNumAnimOverlays();
	for( int layerIndex = 0; layerIndex < layerCount; ++layerIndex )
	{
		CAnimationLayer *currentLayer = pPlayer->GetAnimOverlay(layerIndex);
		if( currentLayer )
		{
			restore->m_layerRecords[layerIndex].m_cycle = currentLayer->m_flCycle;
			restore->m_layerRecords[layerIndex].m_order = currentLayer->m_nOrder;
			restore->m_layerRecords[layerIndex].m_sequence = currentLayer->m_nSequence;
			restore->m_layerRecords[layerIndex].m_weight = currentLayer->m_flWeight;

			bool interpolated = false;
			if( (frac > 0.0f)  &&  interpolationAllowed )
			{
				LayerRecord &recordsLayerRecord = record->m_layerRecords[layerIndex];
				LayerRecord &prevRecordsLayerRecord = prevRecord->m_layerRecords[layerIndex];
				if( (recordsLayerRecord.m_order == prevRecordsLayerRecord.m_order)
					&& (recordsLayerRecord.m_sequence == prevRecordsLayerRecord.m_sequence)
					)
				{
					// We can't interpolate across a sequence or order change
					interpolated = true;
					if( recordsLayerRecord.m_cycle > prevRecordsLayerRecord.m_cycle )
					{
						// the older record is higher in frame than the newer, it must have wrapped around from 1 back to 0
						// add one to the newer so it is lerping from .9 to 1.1 instead of .9 to .1, for example.
						float newCycle = Lerp( frac, recordsLayerRecord.m_cycle, prevRecordsLayerRecord.m_cycle + 1 );
						currentLayer->m_flCycle = newCycle < 1 ? newCycle : newCycle - 1;// and make sure .9 to 1.2 does not end up 1.05
					}
					else
					{
						currentLayer->m_flCycle = Lerp( frac, recordsLayerRecord.m_cycle, prevRecordsLayerRecord.m_cycle  );
					}
					currentLayer->m_nOrder = recordsLayerRecord.m_order;
					currentLayer->m_nSequence = recordsLayerRecord.m_sequence;
					currentLayer->m_flWeight = Lerp( frac, recordsLayerRecord.m_weight, prevRecordsLayerRecord.m_weight  );
				}
			}
			if( !interpolated )
			{
				//Either no interp, or interp failed.  Just use record.
				currentLayer->m_flCycle = record->m_layerRecords[layerIndex].m_cycle;
				currentLayer->m_nOrder = record->m_layerRecords[layerIndex].m_order;
				currentLayer->m_nSequence = record->m_layerRecords[layerIndex].m_sequence;
				currentLayer->m_flWeight = record->m_layerRecords[layerIndex].m_weight;
			}
		}
	}
	
	if ( !flags )
		return; // we didn't change anything

	if ( sv_lagflushbonecache.GetBool() )
		pPlayer->InvalidateBoneCache();

	/*char text[256]; Q_snprintf( text, sizeof(text), "time %.2f", flTargetTime );
	pPlayer->DrawServerHitboxes( 10 );
	NDebugOverlay::Text( org, text, false, 10 );
	NDebugOverlay::EntityBounds( pPlayer, 255, 0, 0, 32, 10 ); */

	m_RestorePlayer.Set( pl_index ); //remember that we changed this player
	m_bNeedToRestore = true;  // we changed at least one player
	restore->m_fFlags = flags; // we need to restore these flags
	change->m_fFlags = flags; // we have changed these flags

	if( sv_showlagcompensation.GetInt() == 1 )
	{
		pPlayer->DrawServerHitboxes(4, true);
	}
}
//-----------------------------------------------------------------------------
// Purpose: Called once per frame after all entities have had a chance to think
//-----------------------------------------------------------------------------
void CLagCompensationManager::FrameUpdatePostEntityThink()
{
if ( m_bNeedsAIUpdate ) // AI Patch Addition.
		UpdateAIIndexes(); // only bother if we haven't had one yet // AI Patch Addition.
	else // setting this true here ensures that the update happens at the start of the next frame // AI Patch Addition.
		m_bNeedsAIUpdate = true; // AI Patch Addition.

	if ( (gpGlobals->maxClients <= 1) || !sv_unlag.GetBool() )
	{
		ClearHistory();
		return;
	}
	
	VPROF_BUDGET( "FrameUpdatePostEntityThink", "CLagCompensationManager" );

	// remove all records before that time:
	int flDeadtime = gpGlobals->curtime - sv_maxunlag.GetFloat();

	// Iterate all active players
	for ( int i = 1; i <= gpGlobals->maxClients; i++ )
	{
		CBasePlayer *pPlayer = UTIL_PlayerByIndex( i );

		CUtlFixedLinkedList< LagRecord > *track = &m_PlayerTrack[i-1];

		if ( !pPlayer )
		{
			if ( track->Count() > 0 )
			{
				track->RemoveAll();
			}

			continue;
		}

		Assert( track->Count() < 1000 ); // insanity check

		// remove tail records that are too old
		int tailIndex = track->Tail();
		while ( track->IsValidIndex( tailIndex ) )
		{
			LagRecord &tail = track->Element( tailIndex );

			// if tail is within limits, stop
			if ( tail.m_flSimulationTime >= flDeadtime )
				break;
			
			// remove tail, get new tail
			track->Remove( tailIndex );
			tailIndex = track->Tail();
		}

		// check if head has same simulation time
		if ( track->Count() > 0 )
		{
			LagRecord &head = track->Element( track->Head() );

			// check if player changed simulation time since last time updated
			if ( head.m_flSimulationTime >= pPlayer->GetSimulationTime() )
				continue; // don't add new entry for same or older time
		}

		// add new record to player track
		LagRecord &record = track->Element( track->AddToHead() );

		record.m_fFlags = 0;
		if ( pPlayer->IsAlive() )
		{
			record.m_fFlags |= LC_ALIVE;
		}

		record.m_flSimulationTime	= pPlayer->GetSimulationTime();
		record.m_vecAngles			= pPlayer->GetLocalAngles();
		record.m_vecOrigin			= pPlayer->GetLocalOrigin();
		record.m_vecMaxs			= pPlayer->WorldAlignMaxs();
		record.m_vecMins			= pPlayer->WorldAlignMins();

		int layerCount = pPlayer->GetNumAnimOverlays();
		for( int layerIndex = 0; layerIndex < layerCount; ++layerIndex )
		{
			CAnimationLayer *currentLayer = pPlayer->GetAnimOverlay(layerIndex);
			if( currentLayer )
			{
				record.m_layerRecords[layerIndex].m_cycle = currentLayer->m_flCycle;
				record.m_layerRecords[layerIndex].m_order = currentLayer->m_nOrder;
				record.m_layerRecords[layerIndex].m_sequence = currentLayer->m_nSequence;
				record.m_layerRecords[layerIndex].m_weight = currentLayer->m_flWeight;
			}
		}
		record.m_masterSequence = pPlayer->GetSequence();
		record.m_masterCycle = pPlayer->GetCycle();
	}
//===================
// AI Patch Addition.
//=================== 
	
	// Iterate all active NPCs
	CAI_BaseNPC **ppAIs = g_AI_Manager.AccessAIs();
	int nAIs = g_AI_Manager.NumAIs();

	for ( int i = 0; i < nAIs; i++ )
	{
		CAI_BaseNPC *pNPC = ppAIs[i];
		CUtlFixedLinkedList< LagRecord > *track = &m_EntityTrack[i];

		if ( !pNPC )
		{
			track->RemoveAll();
			continue;
		}

		Assert( track->Count() < 1000 ); // insanity check

		// remove tail records that are too old
		int tailIndex = track->Tail();
		while ( track->IsValidIndex( tailIndex ) )
		{
			LagRecord &tail = track->Element( tailIndex );

			// if tail is within limits, stop
			if ( tail.m_flSimulationTime >= flDeadtime )
				break;
			
			// remove tail, get new tail
			track->Remove( tailIndex );
			tailIndex = track->Tail();
		}

		// check if head has same simulation time
		if ( track->Count() > 0 )
		{
			LagRecord &head = track->Element( track->Head() );

			// check if entity changed simulation time since last time updated
			if ( &head && head.m_flSimulationTime >= pNPC->GetSimulationTime() )
				continue; // don't add new entry for same or older time

			// Simulation Time is set when an entity moves or rotates ...
			// this error occurs when whatever entity it is that breaks it moves or rotates then, presumably?
		}

		// add new record to track
		LagRecord &record = track->Element( track->AddToHead() );

	record.m_fFlags = 0;
		if ( pNPC->IsAlive() )
		{
			record.m_fFlags |= LC_ALIVE;
		}

		record.m_flSimulationTime	= pNPC->GetSimulationTime();
		record.m_vecAngles			= pNPC->GetLocalAngles();
		record.m_vecOrigin			= pNPC->GetLocalOrigin();
		record.m_vecMaxs			= pNPC->WorldAlignMaxs();
		record.m_vecMins			= pNPC->WorldAlignMins();

		int layerCount = pNPC->GetNumAnimOverlays();
		for( int layerIndex = 0; layerIndex < layerCount; ++layerIndex )
		{
			CAnimationLayer *currentLayer = pNPC->GetAnimOverlay(layerIndex);
			if( currentLayer )
			{
				record.m_layerRecords[layerIndex].m_cycle = currentLayer->m_flCycle;
				record.m_layerRecords[layerIndex].m_order = currentLayer->m_nOrder;
				record.m_layerRecords[layerIndex].m_sequence = currentLayer->m_nSequence;
				record.m_layerRecords[layerIndex].m_weight = currentLayer->m_flWeight;
			}
		}
		record.m_masterSequence = pNPC->GetSequence();
		record.m_masterCycle = pNPC->GetCycle();
	}
}
//-----------------------------------------------------------------------------
// Purpose: Called once per frame after all entities have had a chance to think
//-----------------------------------------------------------------------------
void CLagCompensationManager::FrameUpdatePostEntityThink()
{
	if ( (gpGlobals->maxClients <= 1) || !sv_unlag.GetBool() )
	{
		ClearHistory();
		return;
	}
	
	m_flTeleportDistanceSqr = sv_lagcompensation_teleport_dist.GetFloat() * sv_lagcompensation_teleport_dist.GetFloat();

	VPROF_BUDGET( "FrameUpdatePostEntityThink", "CLagCompensationManager" );

	// remove all records before that time:
	int flDeadtime = gpGlobals->curtime - sv_maxunlag.GetFloat();

	// Iterate all active players
	for ( int i = 1; i <= gpGlobals->maxClients; i++ )
	{
		CBasePlayer *pPlayer = UTIL_PlayerByIndex( i );

		CUtlFixedLinkedList< LagRecord > *track = &m_PlayerTrack[i-1];

		if ( !pPlayer )
		{
			if ( track->Count() > 0 )
			{
				track->RemoveAll();
			}

			continue;
		}

		Assert( track->Count() < 1000 ); // insanity check

		// remove tail records that are too old
		int tailIndex = track->Tail();
		while ( track->IsValidIndex( tailIndex ) )
		{
			LagRecord &tail = track->Element( tailIndex );

			// if tail is within limits, stop
			if ( tail.m_flSimulationTime >= flDeadtime )
				break;
			
			// remove tail, get new tail
			track->Remove( tailIndex );
			tailIndex = track->Tail();
		}

		// check if head has same simulation time
		if ( track->Count() > 0 )
		{
			LagRecord &head = track->Element( track->Head() );

			// check if player changed simulation time since last time updated
			if ( head.m_flSimulationTime >= pPlayer->GetSimulationTime() )
				continue; // don't add new entry for same or older time
		}

		// add new record to player track
		LagRecord &record = track->Element( track->AddToHead() );

		record.m_fFlags = 0;
		if ( pPlayer->IsAlive() )
		{
			record.m_fFlags |= LC_ALIVE;
		}

		record.m_flSimulationTime	= pPlayer->GetSimulationTime();
		record.m_vecAngles			= pPlayer->GetLocalAngles();
		record.m_vecOrigin			= pPlayer->GetLocalOrigin();
		record.m_vecMinsPreScaled	= pPlayer->CollisionProp()->OBBMinsPreScaled();
		record.m_vecMaxsPreScaled	= pPlayer->CollisionProp()->OBBMaxsPreScaled();

		int layerCount = pPlayer->GetNumAnimOverlays();
		for( int layerIndex = 0; layerIndex < layerCount; ++layerIndex )
		{
			CAnimationLayer *currentLayer = pPlayer->GetAnimOverlay(layerIndex);
			if( currentLayer )
			{
				record.m_layerRecords[layerIndex].m_cycle = currentLayer->m_flCycle;
				record.m_layerRecords[layerIndex].m_order = currentLayer->m_nOrder;
				record.m_layerRecords[layerIndex].m_sequence = currentLayer->m_nSequence;
				record.m_layerRecords[layerIndex].m_weight = currentLayer->m_flWeight;
			}
		}
		record.m_masterSequence = pPlayer->GetSequence();
		record.m_masterCycle = pPlayer->GetCycle();
	}

	//Clear the current player.
	m_pCurrentPlayer = NULL;
}