Adjust initial distance when destination is changed for obstacle check

Changed destination may create a situation when the distance actor moved between
2 update calls is less than initial distance because destination has been changed.
This forces actor to take evasive action when there is no actual obstacle.

CHANGELOG.md

@@ -170,6 +170,7 @@
     Bug #6794: Light sources are attached to mesh bounds centers instead of mesh origins when AttachLight NiNode is missing
     Bug #6799: Game crashes if an NPC has no Class attached
     Bug #6849: ImageButton texture is not scaled properly
+    Bug #6860: Sinnammu randomly strafes while running on water
     Bug #6869: Hits queue stagger during swing animation
     Bug #6890: SDL_PeepEvents errors are not handled
     Bug #6895: Removing a negative number of items from a script, makes the script terminate with an error

apps/openmw/mwmechanics/obstacle.cpp

@@ -139,11 +139,18 @@ namespace MWMechanics
             mStateDuration = 0;
             mPrev = position;
             mInitialDistance = (destination - position).length();
+            mDestination = destination;
             return;
         }
 
         if (mWalkState != WalkState::Evade)
         {
+            if (mDestination != destination)
+            {
+                mInitialDistance = (destination - mPrev).length();
+                mDestination = destination;
+            }
+
             const float distSameSpot = DIST_SAME_SPOT * actor.getClass().getCurrentSpeed(actor) * duration;
             const float prevDistance = (destination - mPrev).length();
             const float currentDistance = (destination - position).length();

apps/openmw/mwmechanics/obstacle.hpp

@@ -45,6 +45,7 @@ namespace MWMechanics
 
     private:
         osg::Vec3f mPrev;
+        osg::Vec3f mDestination;
 
         // directions to try moving in when get stuck
         static const float evadeDirections[NUM_EVADE_DIRECTIONS][2];