some checks reworked

apps/openmw/mwclass/npc.hpp

@@ -170,6 +170,14 @@ namespace MWClass
             virtual int getBaseGold(const MWWorld::Ptr& ptr) const;
 
             virtual bool isClass(const MWWorld::Ptr& ptr, const std::string &className) const;
+
+            virtual bool canSwim (const MWWorld::Ptr &ptr) const {
+                return true;
+            }
+
+            virtual bool canWalk (const MWWorld::Ptr &ptr) const {
+                return true;
+            }
     };
 }
 

apps/openmw/mwmechanics/aicombat.cpp

@@ -341,8 +341,8 @@ namespace MWMechanics
 
         // check if can move along z-axis
         bool canMoveByZ;
-        if(canMoveByZ = ((actorCls.isNpc() || actorCls.canSwim(actor)) && MWBase::Environment::get().getWorld()->isSwimming(actor))
+        if(canMoveByZ = (actorCls.canSwim(actor) && MWBase::Environment::get().getWorld()->isSwimming(actor))
-            || (actorCls.canFly(actor) && MWBase::Environment::get().getWorld()->isFlying(actor)))
+            || MWBase::Environment::get().getWorld()->isFlying(actor))
         {
             // determine vertical angle to target
             mMovement.mRotation[0] = getXAngleToDir(vDirToTarget, distToTarget);

apps/openmw/mwworld/physicssystem.cpp

@@ -313,8 +313,9 @@ namespace MWWorld
                 // NOTE: stepMove modifies newPosition if successful
                 if(stepMove(colobj, newPosition, velocity, remainingTime, engine))
                 {
-                    // don't let slaughterfish move out of water after stepMove
+                    // don't let pure water creatures move out of water after stepMove
-                    if(ptr.getClass().canSwim(ptr) && newPosition.z > (waterlevel - halfExtents.z * 0.5))
+                    if((ptr.getClass().canSwim(ptr) && !ptr.getClass().canWalk(ptr)) 
+                            && newPosition.z > (waterlevel - halfExtents.z * 0.5))
                         newPosition = oldPosition;
                     else // Only on the ground if there's gravity
                         isOnGround = !(newPosition.z < waterlevel || isFlying);