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/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;
-                    throwVector = Vector2.Normalize(throwVector);
+                    Vector2 throwVector = Vector2.Normalize(picker.CursorWorldPosition - picker.WorldPosition);
+                    //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
-                        if (diff.Length() > avoidRadius) continue;
+                        float dist = diff.Length();
+                        //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;