Added a bunch of checks to make sure a normalized zero vector (= NaN, NaN) is not used in any position/velocity/movement calculations. There were at least three places where it was causing problems according to error reports: when a character that can't enter a sub spawns at the center of a hull and when using an underwater scooter or throwing something while the cursor is at the position of the character, but there were tons of other places as well where it may have potentially caused physics errors.

Barotrauma/BarotraumaShared/Source/Characters/AI/EnemyAIController.cs

@@ -280,7 +280,9 @@ namespace Barotrauma
                 return;
             }
 
-            SteeringManager.SteeringManual(deltaTime, Vector2.Normalize(SimPosition - selectedAiTarget.SimPosition) * 5);
+            Vector2 escapeDir = Vector2.Normalize(SimPosition - selectedAiTarget.SimPosition);
+            if (!MathUtils.IsValid(escapeDir)) escapeDir = Vector2.UnitY;
+            SteeringManager.SteeringManual(deltaTime, escapeDir * 5);
             SteeringManager.SteeringWander(1.0f);
             SteeringManager.SteeringAvoid(deltaTime, 2f);
         }
@@ -490,8 +492,10 @@ namespace Barotrauma
 
             if (dist < ConvertUnits.ToSimUnits(500.0f))
             {
+                Vector2 attackDir = Vector2.Normalize(Character.SimPosition - attackPosition);
+                if (!MathUtils.IsValid(attackDir)) attackDir = Vector2.UnitY;
                 steeringManager.SteeringSeek(attackPosition, -0.8f);
-                steeringManager.SteeringManual(deltaTime, Vector2.Normalize(Character.SimPosition - attackPosition) * (1.0f - (dist / 500.0f)));
+                steeringManager.SteeringManual(deltaTime, attackDir * (1.0f - (dist / 500.0f)));
             }
 
             steeringManager.SteeringAvoid(deltaTime, 1.0f);

Barotrauma/BarotraumaShared/Source/Characters/AI/Objectives/AIObjectiveCombat.cs

@@ -63,6 +63,7 @@ namespace Barotrauma
                 character.SetInput(InputType.Aim, false, true);
 
                 Vector2 enemyDiff = Vector2.Normalize(enemy.Position - character.Position);
+                if (!MathUtils.IsValid(enemyDiff)) enemyDiff = Rand.Vector(1.0f);
                 float weaponAngle = ((weapon.body.Dir == 1.0f) ? weapon.body.Rotation : weapon.body.Rotation - MathHelper.Pi);
                 Vector2 weaponDir = new Vector2((float)Math.Cos(weaponAngle), (float)Math.Sin(weaponAngle));
 

Barotrauma/BarotraumaShared/Source/Characters/AI/SteeringManager.cs

@@ -80,9 +80,9 @@ namespace Barotrauma
             }
 
             float steeringSpeed = steering.Length();
-            if (steeringSpeed>speed)
+            if (steeringSpeed > speed)
             {
-               steering = Vector2.Normalize(steering) * Math.Abs(speed);
+                steering = Vector2.Normalize(steering) * Math.Abs(speed);
             }
 
             host.Steering = steering;
@@ -97,12 +97,12 @@ namespace Barotrauma
             targetVel = Vector2.Normalize(targetVel) * speed;
             Vector2 newSteering = targetVel - host.Steering;
 
-            if (newSteering==Vector2.Zero) return Vector2.Zero;
+            if (newSteering == Vector2.Zero) return Vector2.Zero;
 
             float steeringSpeed = (newSteering + host.Steering).Length();
             if (steeringSpeed > Math.Abs(speed))
             {
-                newSteering = Vector2.Normalize(newSteering)*Math.Abs(speed);
+                newSteering = Vector2.Normalize(newSteering) * Math.Abs(speed);
             }
 
             return newSteering;
@@ -151,8 +151,7 @@ namespace Barotrauma
                 }
                 else
                 {
-                    Structure closestStructure = closestBody.UserData as Structure;
+                    if (closestBody.UserData is Structure closestStructure)
-                    if (closestStructure != null)
                     {
                         Vector2 obstaclePosition = Submarine.LastPickedPosition;
                         if (closestStructure.IsHorizontal)
@@ -166,15 +165,17 @@ namespace Barotrauma
 
                         avoidSteering = Vector2.Normalize(Submarine.LastPickedPosition - obstaclePosition);
                     }
-                    else if (closestBody.UserData is Item)
+                    else if (closestBody.UserData is Item item)
                     {
-                        Item item = (Item)closestBody.UserData;
                         avoidSteering = Vector2.Normalize(Submarine.LastPickedPosition - item.SimPosition);
                     }
                     else
                     {
                         avoidSteering = Vector2.Normalize(host.SimPosition - Submarine.LastPickedPosition);
                     }
+                    //failed to normalize (the obstacle to avoid is at the same position as the character?)
+                    // -> move to a random direction
+                    if (!MathUtils.IsValid(avoidSteering)) avoidSteering = Rand.Vector(1.0f);
                 }
 
             }

Barotrauma/BarotraumaShared/Source/Characters/Animation/Ragdoll.cs

@@ -766,10 +766,13 @@ namespace Barotrauma
                 //this is preferable to the cost of using continuous collision detection for the character collider
                 if (newHull != null)
                 {
+                    Vector2 hullDiff = WorldPosition - newHull.WorldPosition;
+                    Vector2 moveDir = hullDiff.LengthSquared() < 0.001f ? Vector2.UnitY : Vector2.Normalize(hullDiff);
+
                     //find a position 32 units away from the hull
                     Vector2? intersection = MathUtils.GetLineRectangleIntersection(
                         newHull.WorldPosition, 
-                        newHull.WorldPosition + Vector2.Normalize(WorldPosition - newHull.WorldPosition) * Math.Max(newHull.Rect.Width, newHull.Rect.Height),
+                        newHull.WorldPosition + moveDir * Math.Max(newHull.Rect.Width, newHull.Rect.Height),
                         new Rectangle(newHull.WorldRect.X - 32, newHull.WorldRect.Y + 32, newHull.WorldRect.Width + 64, newHull.Rect.Height + 64));
 
                     if (intersection != null)
@@ -1494,7 +1497,7 @@ namespace Barotrauma
             Vector2 force = Vector2.Zero;
             foreach (Gap gap in Gap.GapList)
             {
-                if (gap.Open <= 0.0f || gap.FlowTargetHull != currentHull || gap.LerpedFlowForce == Vector2.Zero) continue;
+                if (gap.Open <= 0.0f || gap.FlowTargetHull != currentHull || gap.LerpedFlowForce.LengthSquared() < 0.01f) continue;
 
                 Vector2 gapPos = gap.SimPosition;
                 float dist = Vector2.Distance(limbPos, gapPos);

Barotrauma/BarotraumaShared/Source/Items/Components/Holdable/Propulsion.cs

@@ -74,6 +74,8 @@ namespace Barotrauma.Items.Components
             }
 
             Vector2 dir = Vector2.Normalize(character.CursorPosition - character.Position);
+            //move upwards if the cursor is at the position of the character
+            if (!MathUtils.IsValid(dir)) dir = Vector2.UnitY;
 
             Vector2 propulsion = dir * force;
 

Barotrauma/BarotraumaShared/Source/Items/Components/Holdable/Throwable.cs

@@ -94,8 +94,9 @@ namespace Barotrauma.Items.Components
 
                 if (throwPos < -0.0)
                 {
-                    Vector2 throwVector = picker.CursorWorldPosition - picker.WorldPosition;
+                    Vector2 throwVector = Vector2.Normalize(picker.CursorWorldPosition - picker.WorldPosition);
-                    throwVector = Vector2.Normalize(throwVector);
+                    //throw upwards if cursor is at the position of the character
+                    if (!MathUtils.IsValid(throwVector)) throwVector = Vector2.UnitY;
 
                     GameServer.Log(picker.LogName + " threw " + item.Name, ServerLog.MessageType.ItemInteraction);
 

Barotrauma/BarotraumaShared/Source/Items/Components/Machines/Controller.cs

@@ -116,7 +116,7 @@ namespace Barotrauma.Items.Components
                 else
                 {
                     diff.Y = 0.0f;
-                    if (diff != Vector2.Zero && diff.Length() > 10.0f)
+                    if (diff != Vector2.Zero && diff.LengthSquared() > 10.0f * 10.0f)
                     {
                         character.AnimController.TargetMovement = Vector2.Normalize(diff);
                         character.AnimController.TargetDir = diff.X > 0.0f ? Direction.Right : Direction.Left;

Barotrauma/BarotraumaShared/Source/Items/Components/Machines/Steering.cs

@@ -211,8 +211,9 @@ namespace Barotrauma.Items.Components
                     {
                         Vector2 diff = item.Submarine.WorldPosition - (Vector2)intersection;
 
-                        //far enough -> ignore
+                        float dist = diff.Length();
-                        if (diff.Length() > avoidRadius) continue;
+                        //far enough or too close to normalize the diff -> ignore
+                        if (dist > avoidRadius || dist < 0.00001f) continue;
 
                         float dot = item.Submarine.Velocity == Vector2.Zero ?
                             0.0f : Vector2.Dot(item.Submarine.Velocity, -Vector2.Normalize(diff));
@@ -241,16 +242,15 @@ namespace Barotrauma.Items.Components
                 float otherSize = Math.Max(sub.Borders.Width, sub.Borders.Height);
 
                 Vector2 diff = item.Submarine.WorldPosition - sub.WorldPosition;
-
                 float dist = diff == Vector2.Zero ? 0.0f : diff.Length();
 
                 //far enough -> ignore
                 if (dist > thisSize + otherSize) continue;
 
-                diff = Vector2.Normalize(diff);
+                Vector2 dir = dist <= 0.0001f ? Vector2.UnitY : diff / dist;
 
                 float dot = item.Submarine.Velocity == Vector2.Zero ?
-                    0.0f : Vector2.Dot(Vector2.Normalize(item.Submarine.Velocity), -Vector2.Normalize(diff));
+                    0.0f : Vector2.Dot(Vector2.Normalize(item.Submarine.Velocity), -dir);
 
                 //heading away -> ignore
                 if (dot < 0.0f) continue;

Barotrauma/BarotraumaShared/Source/Map/Explosion.cs

@@ -180,6 +180,7 @@ namespace Barotrauma
                     if (limb.WorldPosition != worldPosition && force > 0.0f)
                     {
                         Vector2 limbDiff = Vector2.Normalize(limb.WorldPosition - worldPosition);
+                        if (!MathUtils.IsValid(limbDiff)) limbDiff = Rand.Vector(1.0f);
                         Vector2 impulsePoint = limb.SimPosition - limbDiff * limbRadius;
                         limb.body.ApplyLinearImpulse(limbDiff * distFactor * force, impulsePoint);
                     }

Barotrauma/BarotraumaShared/Source/Map/Levels/Level.cs

@@ -919,7 +919,7 @@ namespace Barotrauma
                     ConvertUnits.ToSimUnits(endPos),
                     null, Physics.CollisionLevel) != null)
                 {
-                    position = ConvertUnits.ToDisplayUnits(Submarine.LastPickedPosition) +  Vector2.Normalize(startPos - endPos)*offsetFromWall;
+                    position = ConvertUnits.ToDisplayUnits(Submarine.LastPickedPosition) + Vector2.Normalize(startPos - endPos) * offsetFromWall;
                     break;
                 }
 

Barotrauma/BarotraumaShared/Source/Map/SubmarineBody.cs

@@ -214,7 +214,7 @@ namespace Barotrauma
                     closestSub = Character.Controlled.Submarine;
                 }
 
-                bool displace = moveAmount.Length() > 100.0f;
+                bool displace = moveAmount.LengthSquared() > 100.0f * 100.0f;
                 foreach (Submarine sub in subsToMove)
                 {
                     sub.PhysicsBody.SetTransform(sub.PhysicsBody.SimPosition + ConvertUnits.ToSimUnits(moveAmount), 0.0f);
@@ -259,7 +259,7 @@ namespace Barotrauma
 
             Vector2 totalForce = CalculateBuoyancy();
 
-            if (Body.LinearVelocity.LengthSquared() > 0.000001f)
+            if (Body.LinearVelocity.LengthSquared() > 0.0001f)
             {
                 float dragCoefficient = 0.01f;
 
@@ -285,6 +285,7 @@ namespace Barotrauma
             worldBorders.Location += MathUtils.ToPoint(ConvertUnits.ToDisplayUnits(Body.SimPosition));
 
             Vector2 translateDir = Vector2.Normalize(subTranslation);
+            if (!MathUtils.IsValid(translateDir)) translateDir = Vector2.UnitY;
 
             foreach (Character c in Character.CharacterList)
             {
@@ -384,7 +385,9 @@ namespace Barotrauma
 
             if (f2.UserData is VoronoiCell cell)
             {
-                HandleLevelCollision(contact, Vector2.Normalize(ConvertUnits.ToDisplayUnits(Body.SimPosition) - cell.Center));
+                Vector2 collisionNormal = Vector2.Normalize(ConvertUnits.ToDisplayUnits(Body.SimPosition) - cell.Center);
+                if (!MathUtils.IsValid(collisionNormal)) collisionNormal = Rand.Vector(1.0f);
+                HandleLevelCollision(contact, collisionNormal);
                 return true;
             }
 
@@ -445,7 +448,9 @@ namespace Barotrauma
         {
             if (limb.Mass > 100.0f)
             {
-                Vector2 normal = Vector2.Normalize(Body.SimPosition - limb.SimPosition);
+                Vector2 normal = Vector2.DistanceSquared(Body.SimPosition, limb.SimPosition) < 0.0001f ?
+                    Vector2.UnitY :
+                    Vector2.Normalize(Body.SimPosition - limb.SimPosition);
 
                 float impact = Math.Min(Vector2.Dot(Velocity - limb.LinearVelocity, -normal), 50.0f) / 5.0f * Math.Min(limb.Mass / 200.0f, 1);
 
@@ -634,7 +639,10 @@ namespace Barotrauma
             float contactDot = Vector2.Dot(otherSub.PhysicsBody.LinearVelocity, -avgContactNormal);
             if (contactDot > 0.0f)
             {
-                otherSub.PhysicsBody.LinearVelocity -= Vector2.Normalize(otherSub.PhysicsBody.LinearVelocity) * contactDot;
+                if (otherSub.PhysicsBody.LinearVelocity.LengthSquared() > 0.0001f)
+                {
+                    otherSub.PhysicsBody.LinearVelocity -= Vector2.Normalize(otherSub.PhysicsBody.LinearVelocity) * contactDot;
+                }
 
                 impact = Vector2.Dot(otherSub.Velocity, normal);
                 otherSub.SubBody.ApplyImpact(impact, normal, contact);

Barotrauma/BarotraumaShared/Source/Map/TransitionCinematic.cs

@@ -89,7 +89,9 @@ namespace Barotrauma
                 foreach (Submarine sub in subs)
                 {
                     if (sub.Position == targetPos) continue;
-                    sub.ApplyForce((Vector2.Normalize(targetPos - sub.Position) * targetSpeed - sub.Velocity) * 500.0f);
+                    Vector2 dir = Vector2.Normalize(targetPos - sub.Position);
+                    if (!MathUtils.IsValid(dir)) continue;
+                    sub.ApplyForce((dir * targetSpeed - sub.Velocity) * 500.0f);
                 }
                 
                 timer += CoroutineManager.UnscaledDeltaTime;

Barotrauma/BarotraumaShared/Source/Networking/RespawnManager.cs

@@ -362,8 +362,12 @@ namespace Barotrauma.Networking
 
             while (Math.Abs(position.Y - respawnShuttle.WorldPosition.Y) > 100.0f)
             {
-                Vector2 displayVel = Vector2.Normalize(position - respawnShuttle.WorldPosition) * speed;
+                Vector2 diff = position - respawnShuttle.WorldPosition;
-                respawnShuttle.SubBody.Body.LinearVelocity = ConvertUnits.ToSimUnits(displayVel);
+                if (diff.LengthSquared() > 0.01f)
+                {
+                    Vector2 displayVel = Vector2.Normalize(diff) * speed;
+                    respawnShuttle.SubBody.Body.LinearVelocity = ConvertUnits.ToSimUnits(displayVel);
+                }
                 yield return CoroutineStatus.Running;
 
                 if (respawnShuttle.SubBody == null) yield return CoroutineStatus.Success;