Apply uniform random deviation to AI reaction timer

This allows to distribute AI reaction calls over time.

Before this change actors appearing at the same frame will react in the same
frame over and over because AI reaction period is constant. It creates a
non-uniform CPU usage over frames. If a single frame has too many AI reactions
it may cause stuttering when there are too many actors on a scene for current
system.

Another concern is a synchronization of actions between creatures and NPC.
They start to go or hit at the same frame that is unnatural.

apps/openmw/mwmechanics/aicombat.cpp

@@ -146,19 +146,10 @@ namespace MWMechanics
         }
         storage.mActionCooldown -= duration;
 
-        float& timerReact = storage.mTimerReact;
-        if (timerReact < AI_REACTION_TIME)
-        {
-            timerReact += duration;
-        }
-        else
-        {
-            timerReact = 0;
-            if (attack(actor, target, storage, characterController))
-                return true;
-        }
+        if (storage.mReaction.update(duration) == Misc::TimerStatus::Waiting)
+            return false;
 
-        return false;
+        return attack(actor, target, storage, characterController);
     }
 
     bool AiCombat::attack(const MWWorld::Ptr& actor, const MWWorld::Ptr& target, AiCombatStorage& storage, CharacterController& characterController)

apps/openmw/mwmechanics/aicombat.hpp

@@ -10,6 +10,7 @@
 #include "pathfinding.hpp"
 #include "movement.hpp"
 #include "obstacle.hpp"
+#include "aitimer.hpp"
 
 namespace ESM
 {
@@ -27,7 +28,7 @@ namespace MWMechanics
     struct AiCombatStorage : AiTemporaryBase
     {
         float mAttackCooldown;
-        float mTimerReact;
+        AiReactionTimer mReaction;
         float mTimerCombatMove;
         bool mReadyToAttack;
         bool mAttack;
@@ -60,7 +61,6 @@ namespace MWMechanics
 
         AiCombatStorage():
         mAttackCooldown(0.0f),
-        mTimerReact(AI_REACTION_TIME),
         mTimerCombatMove(0.0f),
         mReadyToAttack(false),
         mAttack(false),

apps/openmw/mwmechanics/aipackage.cpp

@@ -28,7 +28,6 @@
 MWMechanics::AiPackage::AiPackage(AiPackageTypeId typeId, const Options& options) :
     mTypeId(typeId),
     mOptions(options),
-    mTimer(AI_REACTION_TIME + 1.0f), // to force initial pathbuild
     mTargetActorRefId(""),
     mTargetActorId(-1),
     mRotateOnTheRunChecks(0),
@@ -64,7 +63,7 @@ MWWorld::Ptr MWMechanics::AiPackage::getTarget() const
 void MWMechanics::AiPackage::reset()
 {
     // reset all members
-    mTimer = AI_REACTION_TIME + 1.0f;
+    mReaction.reset();
     mIsShortcutting = false;
     mShortcutProhibited = false;
     mShortcutFailPos = osg::Vec3f();
@@ -75,7 +74,7 @@ void MWMechanics::AiPackage::reset()
 
 bool MWMechanics::AiPackage::pathTo(const MWWorld::Ptr& actor, const osg::Vec3f& dest, float duration, float destTolerance)
 {
-    mTimer += duration; //Update timer
+    const Misc::TimerStatus timerStatus = mReaction.update(duration);
 
     const osg::Vec3f position = actor.getRefData().getPosition().asVec3(); //position of the actor
     MWBase::World* world = MWBase::Environment::get().getWorld();
@@ -98,7 +97,7 @@ bool MWMechanics::AiPackage::pathTo(const MWWorld::Ptr& actor, const osg::Vec3f&
     const bool isDestReached = (distToTarget <= destTolerance);
     const bool actorCanMoveByZ = canActorMoveByZAxis(actor);
 
-    if (!isDestReached && mTimer > AI_REACTION_TIME)
+    if (!isDestReached && timerStatus == Misc::TimerStatus::Elapsed)
     {
         if (actor.getClass().isBipedal(actor))
             openDoors(actor);
@@ -142,8 +141,6 @@ bool MWMechanics::AiPackage::pathTo(const MWWorld::Ptr& actor, const osg::Vec3f&
                     mPathFinder.addPointToPath(dest); //Adds the final destination to the path, to try to get to where you want to go
             }
         }
-
-        mTimer = 0;
     }
 
     const float actorTolerance = 2 * actor.getClass().getMaxSpeed(actor) * duration

apps/openmw/mwmechanics/aipackage.hpp

@@ -10,6 +10,7 @@
 #include "obstacle.hpp"
 #include "aistate.hpp"
 #include "aipackagetypeid.hpp"
+#include "aitimer.hpp"
 
 namespace MWWorld
 {
@@ -28,8 +29,6 @@ namespace ESM
 
 namespace MWMechanics
 {
-    const float AI_REACTION_TIME = 0.25f;
-
     class CharacterController;
     class PathgridGraph;
 
@@ -158,7 +157,7 @@ namespace MWMechanics
             PathFinder mPathFinder;
             ObstacleCheck mObstacleCheck;
 
-            float mTimer;
+            AiReactionTimer mReaction;
 
             std::string mTargetActorRefId;
             mutable int mTargetActorId;

apps/openmw/mwmechanics/aitimer.hpp

@@ -0,0 +1,26 @@
+#ifndef OPENMW_MECHANICS_AITIMER_H
+#define OPENMW_MECHANICS_AITIMER_H
+
+#include <components/misc/rng.hpp>
+#include <components/misc/timer.hpp>
+
+namespace MWMechanics
+{
+    constexpr float AI_REACTION_TIME = 0.25f;
+
+    class AiReactionTimer
+    {
+        public:
+            static constexpr float sDeviation = 0.1f;
+
+            Misc::TimerStatus update(float duration) { return mImpl.update(duration); }
+
+            void reset() { mImpl.reset(Misc::Rng::deviate(0, sDeviation)); }
+
+        private:
+            Misc::DeviatingPeriodicTimer mImpl {AI_REACTION_TIME, sDeviation,
+                                                Misc::Rng::deviate(0, sDeviation)};
+    };
+}
+
+#endif

apps/openmw/mwmechanics/aiwander.cpp

@@ -223,15 +223,10 @@ namespace MWMechanics
 
         doPerFrameActionsForState(actor, duration, storage);
 
-        float& lastReaction = storage.mReaction;
-        lastReaction += duration;
-        if (AI_REACTION_TIME <= lastReaction)
-        {
-            lastReaction = 0;
-            return reactionTimeActions(actor, storage, pos);
-        }
-        else
+        if (storage.mReaction.update(duration) == Misc::TimerStatus::Waiting)
             return false;
+
+        return reactionTimeActions(actor, storage, pos);
     }
 
     bool AiWander::reactionTimeActions(const MWWorld::Ptr& actor, AiWanderStorage& storage, ESM::Position& pos)

apps/openmw/mwmechanics/aiwander.hpp

@@ -10,6 +10,7 @@
 #include "pathfinding.hpp"
 #include "obstacle.hpp"
 #include "aistate.hpp"
+#include "aitimer.hpp"
 
 namespace ESM
 {
@@ -25,7 +26,7 @@ namespace MWMechanics
     /// \brief This class holds the variables AiWander needs which are deleted if the package becomes inactive.
     struct AiWanderStorage : AiTemporaryBase
     {
-        float mReaction; // update some actions infrequently
+        AiReactionTimer mReaction;
 
         // AiWander states
         enum WanderState
@@ -57,7 +58,6 @@ namespace MWMechanics
         int mStuckCount;
 
         AiWanderStorage():
-            mReaction(0),
             mState(Wander_ChooseAction),
             mIsWanderingManually(false),
             mCanWanderAlongPathGrid(true),

components/misc/rng.cpp

@@ -47,4 +47,9 @@ namespace Misc
     {
         return static_cast<unsigned int>(std::chrono::high_resolution_clock::now().time_since_epoch().count());
     }
+
+    float Rng::deviate(float mean, float deviation, Seed& seed)
+    {
+        return std::uniform_real_distribution<float>(mean - deviation, mean + deviation)(seed.mGenerator);
+    }
 }

components/misc/rng.hpp

@@ -42,6 +42,8 @@ public:
 
     /// returns default seed for RNG
     static unsigned int generateDefaultSeed();
+
+    static float deviate(float mean, float deviation, Seed& seed = getSeed());
 };
 
 }

components/misc/timer.hpp

@@ -0,0 +1,42 @@
+#ifndef OPENMW_COMPONENTS_MISC_TIMER_H
+#define OPENMW_COMPONENTS_MISC_TIMER_H
+
+#include "rng.hpp"
+
+namespace Misc
+{
+    enum class TimerStatus
+    {
+        Waiting,
+        Elapsed,
+    };
+
+    class DeviatingPeriodicTimer
+    {
+        public:
+            explicit DeviatingPeriodicTimer(float period, float deviation, float timeLeft)
+                : mPeriod(period), mDeviation(deviation), mTimeLeft(timeLeft)
+            {}
+
+            TimerStatus update(float duration)
+            {
+                if (mTimeLeft > 0)
+                {
+                    mTimeLeft -= duration;
+                    return TimerStatus::Waiting;
+                }
+
+                mTimeLeft = Rng::deviate(mPeriod, mDeviation);
+                return TimerStatus::Elapsed;
+            }
+
+            void reset(float timeLeft) { mTimeLeft = timeLeft; }
+
+        private:
+            const float mPeriod;
+            const float mDeviation;
+            float mTimeLeft;
+    };
+}
+
+#endif