Modify the way swimming is handled:

- compute the swimming state instead of storing it, it changes as part of the simulation and was not updated, so it was wrong anyway.
- store the swim level in ActorFrameData, it is constant per Actor so no need to compute it inside the simulation

apps/openmw/mwphysics/movementsolver.cpp

@@ -140,8 +140,7 @@ namespace MWPhysics
         osg::Vec3f halfExtents = physicActor->getHalfExtents();
         actor.mPosition.z() += halfExtents.z(); // vanilla-accurate
 
-        static const float fSwimHeightScale = MWBase::Environment::get().getWorld()->getStore().get<ESM::GameSetting>().find("fSwimHeightScale")->mValue.getFloat();
-        float swimlevel = actor.mWaterlevel + halfExtents.z() - (physicActor->getRenderingHalfExtents().z() * 2 * fSwimHeightScale);
+        float swimlevel = actor.mSwimLevel + halfExtents.z();
 
         ActorTracer tracer;
 

apps/openmw/mwphysics/mtphysics.cpp

@@ -49,13 +49,18 @@ namespace
             bool mCanBeSharedLock;
     };
 
+    bool isUnderWater(const MWPhysics::ActorFrameData& actorData)
+    {
+        return actorData.mPosition.z() < actorData.mSwimLevel;
+    }
+
     void handleFall(MWPhysics::ActorFrameData& actorData, bool simulationPerformed)
     {
         const float heightDiff = actorData.mPosition.z() - actorData.mOldHeight;
 
         const bool isStillOnGround = (simulationPerformed && actorData.mWasOnGround && actorData.mIsOnGround);
 
-        if (isStillOnGround || actorData.mFlying || actorData.mSwimming || actorData.mSlowFall < 1)
+        if (isStillOnGround || actorData.mFlying || isUnderWater(actorData) || actorData.mSlowFall < 1)
             actorData.mNeedLand = true;
         else if (heightDiff < 0)
             actorData.mFallHeight += heightDiff;
@@ -67,7 +72,7 @@ namespace
 
         MWMechanics::CreatureStats& stats = ptr.getClass().getCreatureStats(ptr);
         if (actorData.mNeedLand)
-            stats.land(ptr == MWMechanics::getPlayer() && (actorData.mFlying || actorData.mSwimming));
+            stats.land(ptr == MWMechanics::getPlayer() && (actorData.mFlying || isUnderWater(actorData)));
         else if (actorData.mFallHeight < 0)
             stats.addToFallHeight(-actorData.mFallHeight);
     }

apps/openmw/mwphysics/physicssystem.cpp

@@ -1007,10 +1007,11 @@ namespace MWPhysics
         const MWBase::World *world = MWBase::Environment::get().getWorld();
         const auto ptr = actor->getPtr();
         mFlying = world->isFlying(ptr);
-        mSwimming = world->isSwimming(ptr);
         const auto& stats = ptr.getClass().getCreatureStats(ptr);
         const bool godmode = ptr == world->getPlayerConstPtr() && world->getGodModeState();
         mInert = stats.isDead() || (!godmode && stats.getMagicEffects().get(ESM::MagicEffect::Paralyze).getModifier() > 0);
+        static const float fSwimHeightScale = MWBase::Environment::get().getWorld()->getStore().get<ESM::GameSetting>().find("fSwimHeightScale")->mValue.getFloat();
+        mSwimLevel = mWaterlevel - (actor->getRenderingHalfExtents().z() * 2 * fSwimHeightScale);
     }
 
     void ActorFrameData::updatePosition(btCollisionWorld* world)

apps/openmw/mwphysics/physicssystem.hpp

@@ -84,7 +84,6 @@ namespace MWPhysics
         Actor* mActorRaw;
         MWWorld::Ptr mStandingOn;
         bool mFlying;
-        bool mSwimming;
         bool mWasOnGround;
         bool mIsOnGround;
         bool mIsOnSlope;
@@ -94,6 +93,7 @@ namespace MWPhysics
         bool mWalkingOnWater;
         bool mSkipCollisionDetection;
         float mWaterlevel;
+        float mSwimLevel;
         float mSlowFall;
         float mOldHeight;
         float mFallHeight;