Optimize short-trace test to only be done when particularly helpful

apps/openmw/mwphysics/movementsolver.cpp

@@ -203,7 +203,7 @@ namespace MWPhysics
             if((newPosition - nextpos).length2() > 0.0001)
             {
                 // trace to where character would go if there were no obstructions
-                tracer.doTrace(actor.mCollisionObject, newPosition, nextpos, collisionWorld);
+                tracer.doTrace(actor.mCollisionObject, newPosition, nextpos, collisionWorld, actor.mIsOnGround);
 
                 // check for obstructions
                 if(tracer.mFraction >= 1.0f)
@@ -338,7 +338,7 @@ namespace MWPhysics
             osg::Vec3f from = newPosition;
             auto dropDistance = 2*sGroundOffset + (actor.mIsOnGround ? sStepSizeDown : 0);
             osg::Vec3f to = newPosition - osg::Vec3f(0,0,dropDistance);
-            tracer.doTrace(actor.mCollisionObject, from, to, collisionWorld);
+            tracer.doTrace(actor.mCollisionObject, from, to, collisionWorld, actor.mIsOnGround);
             if(tracer.mFraction < 1.0f)
             {
                 if (!isActor(tracer.mHitObject))

apps/openmw/mwphysics/stepper.cpp

@@ -36,7 +36,7 @@ namespace MWPhysics
         // Stairstepping algorithms work by moving up to avoid the step, moving forwards, then moving back down onto the ground.
         // This algorithm has a couple of minor problems, but they don't cause problems for sane geometry, and just prevent stepping on insane geometry.
 
-        mUpStepper.doTrace(mColObj, position, position + osg::Vec3f(0.0f, 0.0f, Constants::sStepSizeUp), mColWorld);
+        mUpStepper.doTrace(mColObj, position, position + osg::Vec3f(0.0f, 0.0f, Constants::sStepSizeUp), mColWorld, onGround);
 
         float upDistance = 0;
         if(!mUpStepper.mHitObject)
@@ -117,7 +117,7 @@ namespace MWPhysics
                 downStepSize = upDistance;
             else
                 downStepSize = moveDistance + upDistance + sStepSizeDown;
-            mDownStepper.doTrace(mColObj, tracerDest, tracerDest + osg::Vec3f(0.0f, 0.0f, -downStepSize), mColWorld);
+            mDownStepper.doTrace(mColObj, tracerDest, tracerDest + osg::Vec3f(0.0f, 0.0f, -downStepSize), mColWorld, onGround);
 
             // can't step down onto air, non-walkable-slopes, or actors
             // NOTE: using a capsule causes isWalkableSlope (used in canStepDown) to fail on certain geometry that were intended to be valid at the bottoms of stairs

apps/openmw/mwphysics/trace.cpp

@@ -24,45 +24,57 @@ ActorConvexCallback sweepHelper(const btCollisionObject *actor, const btVector3&
     assert(shape->isConvex());
 
     const btVector3 motion = from - to; // FIXME: this is backwards; means ActorConvexCallback is doing dot product tests backwards too
-    ActorConvexCallback newTraceCallback(actor, motion, btScalar(0.0), world);
+    ActorConvexCallback traceCallback(actor, motion, btScalar(0.0), world);
     // Inherit the actor's collision group and mask
-    newTraceCallback.m_collisionFilterGroup = actor->getBroadphaseHandle()->m_collisionFilterGroup;
-    newTraceCallback.m_collisionFilterMask = actor->getBroadphaseHandle()->m_collisionFilterMask;
+    traceCallback.m_collisionFilterGroup = actor->getBroadphaseHandle()->m_collisionFilterGroup;
+    traceCallback.m_collisionFilterMask = actor->getBroadphaseHandle()->m_collisionFilterMask;
     if(actorFilter)
-        newTraceCallback.m_collisionFilterMask &= ~CollisionType_Actor;
+        traceCallback.m_collisionFilterMask &= ~CollisionType_Actor;
 
-    world->convexSweepTest(static_cast<const btConvexShape*>(shape), transFrom, transTo, newTraceCallback);
-    return newTraceCallback;
+    world->convexSweepTest(static_cast<const btConvexShape*>(shape), transFrom, transTo, traceCallback);
+    return traceCallback;
 }
 
-void ActorTracer::doTrace(const btCollisionObject *actor, const osg::Vec3f& start, const osg::Vec3f& end, const btCollisionWorld* world)
+void ActorTracer::doTrace(const btCollisionObject *actor, const osg::Vec3f& start, const osg::Vec3f& end, const btCollisionWorld* world, bool attempt_short_trace)
 {
     const btVector3 btstart = Misc::Convert::toBullet(start);
     btVector3 btend = Misc::Convert::toBullet(end);
 
-    bool do_fallback = false;
-    if((btend-btstart).length2() > 5.0*5.0)
+    // Because Bullet's collision trace tests touch *all* geometry in its path, a lot of long collision tests
+    // will unnecessarily test against complex meshes that are dozens of units away. This wouldn't normally be
+    // a problem, but bullet isn't the fastest in the world when it comes to doing tests against triangle meshes.
+    // Therefore, we try out a short trace first, then only fall back to the full length trace if needed.
+    // This trace needs to be at least a couple units long, but there's no one particular ideal length.
+    // The length of 2.1 chosen here is a "works well in practice after testing a few random lengths" value.
+    // (Also, we only do this short test if the intended collision trace is long enough for it to make sense.)
+    const float fallback_length = 2.1f;
+    bool doing_short_trace = false;
+    // For some reason, typical scenes perform a little better if we increase the threshold length for the length test.
+    // (Multiplying by 2 in 'square distance' units gives us about 1.4x the threshold length. In benchmarks this was
+    //  slightly better for the performance of normal scenes than 4.0, and just plain better than 1.0.)
+    if(attempt_short_trace && (btend-btstart).length2() > fallback_length*fallback_length*2.0)
     {
-        btend = btstart + (btend-btstart).normalized()*5.0;
-        do_fallback = true;
+        btend = btstart + (btend-btstart).normalized()*fallback_length;
+        doing_short_trace = true;
     }
 
-    auto newTraceCallback = sweepHelper(actor, btstart, btend, world, false);
+    auto traceCallback = sweepHelper(actor, btstart, btend, world, false);
 
     // Copy the hit data over to our trace results struct:
-    if(newTraceCallback.hasHit())
+    if(traceCallback.hasHit())
     {
-        mFraction = newTraceCallback.m_closestHitFraction;
-        if((end-start).length2() > 0.0)
+        mFraction = traceCallback.m_closestHitFraction;
+        // ensure fraction is correct (covers intended distance traveled instead of actual distance traveled)
+        if(doing_short_trace && (end-start).length2() > 0.0)
             mFraction *= (btend-btstart).length() / (end-start).length();
-        mPlaneNormal = Misc::Convert::toOsg(newTraceCallback.m_hitNormalWorld);
+        mPlaneNormal = Misc::Convert::toOsg(traceCallback.m_hitNormalWorld);
         mEndPos = (end-start)*mFraction + start;
-        mHitPoint = Misc::Convert::toOsg(newTraceCallback.m_hitPointWorld);
-        mHitObject = newTraceCallback.m_hitCollisionObject;
+        mHitPoint = Misc::Convert::toOsg(traceCallback.m_hitPointWorld);
+        mHitObject = traceCallback.m_hitCollisionObject;
     }
     else
     {
-        if(do_fallback)
+        if(doing_short_trace)
         {
             btend = Misc::Convert::toBullet(end);
             auto newTraceCallback = sweepHelper(actor, btstart, btend, world, false);

apps/openmw/mwphysics/trace.h

@@ -20,7 +20,7 @@ namespace MWPhysics
 
         float mFraction;
 
-        void doTrace(const btCollisionObject *actor, const osg::Vec3f& start, const osg::Vec3f& end, const btCollisionWorld* world);
+        void doTrace(const btCollisionObject *actor, const osg::Vec3f& start, const osg::Vec3f& end, const btCollisionWorld* world, bool attempt_short_trace = false);
         void findGround(const Actor* actor, const osg::Vec3f& start, const osg::Vec3f& end, const btCollisionWorld* world);
     };
 }