Duck under low headroom the navmesh does not mark as crouch

src/game/server/neo/bot/neo_bot_locomotion.cpp

@@ -6,6 +6,13 @@
 
 extern ConVar falldamage;
 
+// How far towards its move goal a bot checks its headroom: at least about a hull width, so it ducks at the
+// obstacle rather than a long way before it,
+static const float NEO_BOT_HEADROOM_LOOKAHEAD = 32.0f;
+// and how often, while the crouch press of one check lasts until the next
+static const float NEO_BOT_HEADROOM_CHECK_INTERVAL = 0.2f;
+static const float NEO_BOT_HEADROOM_CROUCH_HOLD = 0.3f;
+
 //-----------------------------------------------------------------------------------------
 void CNEOBotLocomotion::Update( void )
 {
@@ -56,6 +63,90 @@ void CNEOBotLocomotion::Approach( const Vector& pos, float goalWeight )
 }
 
 
+//-----------------------------------------------------------------------------------------
+// Duck when a standing hull would hit something just ahead but a crouched one would not: a beam,
+// light fitting or lintel at head height. The bot template this came from never crouched to navigate
+void CNEOBotLocomotion::AdjustPosture( const Vector &moveGoal )
+{
+	if ( !IsOnGround() )
+	{
+		return;
+	}
+
+	CNEOBot *me = ToNEOBot( GetBot()->GetEntity() );
+	if ( !me || me->IsBotOnLadder() )
+	{
+		return;
+	}
+
+	// A crouch area already holds the duck, and a bot at a ladder's foot or top lines up with the ladder standing
+	const CNavArea *area = me->GetLastKnownArea();
+	if ( area && ( area->HasAttributes( NAV_MESH_CROUCH ) || IsLadderEnd( area ) ) )
+	{
+		return;
+	}
+
+	if ( !m_headroomTimer.IsElapsed() )
+	{
+		return;
+	}
+
+	m_headroomTimer.Start( NEO_BOT_HEADROOM_CHECK_INTERVAL );
+
+	// look as far as the bot moves before the next check, plus a hull width
+	const float flReach = MAX( NEO_BOT_HEADROOM_LOOKAHEAD,
+		GetGroundSpeed() * NEO_BOT_HEADROOM_CHECK_INTERVAL + GetBot()->GetBodyInterface()->GetHullWidth() );
+	if ( IsOnlyCrouchClearAhead( moveGoal, flReach ) )
+	{
+		me->PressCrouchButton( NEO_BOT_HEADROOM_CROUCH_HOLD );
+	}
+}
+
+
+//-----------------------------------------------------------------------------------------
+bool CNEOBotLocomotion::IsLadderEnd( const CNavArea *area )
+{
+	return area->GetLadders( CNavLadder::LADDER_UP )->Count() > 0
+		|| area->GetLadders( CNavLadder::LADDER_DOWN )->Count() > 0;
+}
+
+
+//-----------------------------------------------------------------------------------------
+bool CNEOBotLocomotion::IsOnlyCrouchClearAhead( const Vector &moveGoal, float flReach ) const
+{
+	const Vector &feet = GetFeet();
+	Vector toGoal = moveGoal - feet;
+	toGoal.z = 0.0f;
+	const float flGoalDist = toGoal.NormalizeInPlace();
+	if ( flGoalDist < 1.0f )
+	{
+		return false;
+	}
+
+	// Sweep from step height up, so a step the bot can walk onto does not count as blocking
+	const IBody *body = GetBot()->GetBodyInterface();
+	const float flStep = GetStepHeight();
+	const float flHalfWidth = 0.5f * body->GetHullWidth();
+	const Vector mins( -flHalfWidth, -flHalfWidth, 0.0f );
+	const Vector standMaxs( flHalfWidth, flHalfWidth, body->GetStandHullHeight() - flStep );
+	const Vector crouchMaxs( flHalfWidth, flHalfWidth, body->GetCrouchHullHeight() - flStep );
+	const Vector from = feet + Vector( 0.0f, 0.0f, flStep );
+	const Vector to = from + toGoal * Min( flGoalDist, flReach );
+
+	// Players move out of the way, so only the world and props count
+	NextBotTraceFilterIgnoreActors filter( GetBot()->GetEntity(), COLLISION_GROUP_NONE );
+	trace_t trace;
+	TraceHull( from, to, mins, standMaxs, body->GetSolidMask(), &filter, &trace );
+	if ( trace.fraction >= 1.0f && !trace.startsolid )
+	{
+		return false;
+	}
+
+	TraceHull( from, to, mins, crouchMaxs, body->GetSolidMask(), &filter, &trace );
+	return trace.fraction >= 1.0f && !trace.startsolid;
+}
+
+
 //-----------------------------------------------------------------------------------------
 // Distance at which we will die if we fall
 float CNEOBotLocomotion::GetDeathDropHeight( void ) const

src/game/server/neo/bot/neo_bot_locomotion.h

@@ -31,7 +31,13 @@ class CNEOBotLocomotion : public PlayerLocomotion
 	virtual bool IsEntityTraversable( CBaseEntity *obstacle, TraverseWhenType when = EVENTUALLY ) const;
 
 protected:
-	virtual void AdjustPosture( const Vector &moveGoal ) { }	// never crouch to navigate
+	virtual void AdjustPosture( const Vector &moveGoal );	// duck when only a crouched hull fits ahead
+
+private:
+	bool IsOnlyCrouchClearAhead( const Vector &moveGoal, float flReach ) const;
+	static bool IsLadderEnd( const CNavArea *area );
+
+	CountdownTimer m_headroomTimer;
 };
 
 inline float CNEOBotLocomotion::GetMaxJumpHeight( void ) const