Optimize actor physics: Use only one convexSweepTest for stepping down and checking onGround status, instead of 2

apps/openmw/mwworld/physicssystem.cpp

@@ -286,8 +286,9 @@ namespace MWWorld
              */
 
             OEngine::Physic::ActorTracer tracer;
-            bool wasOnGround = false;
-            bool isOnGround = false;
+            bool isOnGround = physicActor->getOnGround();
+            if (movement.z > 0.f)
+                isOnGround = false;
             Ogre::Vector3 inertia(0.0f);
             Ogre::Vector3 velocity;
 
@@ -320,23 +321,6 @@ namespace MWWorld
                         velocity = newVelocity;
                 }
                 inertia = velocity; // NOTE: velocity is for z axis only in this code block
-
-                if(!(movement.z > 0.0f)) // falling or moving horizontally (or stationary?) check if we're on ground now
-                {
-                    wasOnGround = physicActor->getOnGround(); // store current state
-                    tracer.doTrace(colobj, position, position - Ogre::Vector3(0,0,2), engine); // check if down 2 possible
-                    if(tracer.mFraction < 1.0f && getSlope(tracer.mPlaneNormal) <= sMaxSlope)
-                    {
-                        const btCollisionObject* standingOn = tracer.mHitObject;
-                        if (const OEngine::Physic::RigidBody* body = dynamic_cast<const OEngine::Physic::RigidBody*>(standingOn))
-                        {
-                            standingCollisionTracker[ptr.getRefData().getHandle()] = body->mName;
-                        }
-                        isOnGround = true;
-                        // if we're on the ground, don't try to fall any more
-                        velocity.z = std::max(0.0f, velocity.z);
-                    }
-                }
             }
             ptr.getClass().getMovementSettings(ptr).mPosition[2] = 0;
 
@@ -439,12 +423,22 @@ namespace MWWorld
                 }
             }
 
-            if(isOnGround || wasOnGround)
+            if (!(inertia.z > 0.f) && !(newPosition.z < waterlevel || isFlying))
             {
-                tracer.doTrace(colobj, newPosition, newPosition - Ogre::Vector3(0,0,sStepSize+2.0f), engine);
+                Ogre::Vector3 from = newPosition;
+                Ogre::Vector3 to = newPosition - (isOnGround ?
+                             Ogre::Vector3(0,0,sStepSize+2.f) : Ogre::Vector3(0,0,2.f));
+                tracer.doTrace(colobj, from, to, engine);
                 if(tracer.mFraction < 1.0f && getSlope(tracer.mPlaneNormal) <= sMaxSlope)
                 {
+                    const btCollisionObject* standingOn = tracer.mHitObject;
+                    if (const OEngine::Physic::RigidBody* body = dynamic_cast<const OEngine::Physic::RigidBody*>(standingOn))
+                    {
+                        standingCollisionTracker[ptr.getRefData().getHandle()] = body->mName;
+                    }
+
                     newPosition.z = tracer.mEndPos.z + 1.0f;
+
                     isOnGround = true;
                 }
                 else