From 8766de21cc0b7cf9e46fdd01656fb770dcfa2122 Mon Sep 17 00:00:00 2001
From: Roman <69218254+amzn-rhhong@users.noreply.github.com>
Date: Tue, 25 Jan 2022 14:53:16 -0800
Subject: [PATCH] Only use a deterministic random when network option is
 enabled. (#7126)

* Only use a deterministic random when network option is enabled.

Signed-off-by: rhhong <rhhong@amazon.com>

* use actor instance id as the seed of the lcg random in anim graph instance

Signed-off-by: rhhong <rhhong@amazon.com>

* add const

Signed-off-by: rhhong <rhhong@amazon.com>
---
 .../Code/EMotionFX/Source/AnimGraphInstance.cpp  |  3 +++
 .../EMotionFX/Source/AnimGraphTimeCondition.cpp  | 11 ++---------
 Gems/EMotionFX/Code/MCore/Source/Random.h        | 16 ----------------
 3 files changed, 5 insertions(+), 25 deletions(-)

diff --git a/Gems/EMotionFX/Code/EMotionFX/Source/AnimGraphInstance.cpp b/Gems/EMotionFX/Code/EMotionFX/Source/AnimGraphInstance.cpp
index 7f9e8ba6fc..61a366f298 100644
--- a/Gems/EMotionFX/Code/EMotionFX/Source/AnimGraphInstance.cpp
+++ b/Gems/EMotionFX/Code/EMotionFX/Source/AnimGraphInstance.cpp
@@ -71,6 +71,9 @@ namespace EMotionFX
         // create the parameter value objects
         CreateParameterValues();
 
+        // Assign a unique seed for the lcg random number. Here we use the actorInstanceId because it guaranteed to be unique and available on actor instances.
+        m_lcgRandom.SetSeed(actorInstance->GetID());
+
         m_animGraph->Unlock();
         GetEventManager().OnCreateAnimGraphInstance(this);
     }
diff --git a/Gems/EMotionFX/Code/EMotionFX/Source/AnimGraphTimeCondition.cpp b/Gems/EMotionFX/Code/EMotionFX/Source/AnimGraphTimeCondition.cpp
index 3da55ced3e..e6e9c529df 100644
--- a/Gems/EMotionFX/Code/EMotionFX/Source/AnimGraphTimeCondition.cpp
+++ b/Gems/EMotionFX/Code/EMotionFX/Source/AnimGraphTimeCondition.cpp
@@ -90,15 +90,8 @@ namespace EMotionFX
         if (m_useRandomization)
         {
             // create a randomized count down value
-            if (animGraphInstance->IsNetworkEnabled())
-            {
-                // using a seeded random in order to generate predictable result in network. 
-                uniqueData->m_countDownTime = MCore::Random::RandF(m_minRandomTime, m_maxRandomTime, animGraphInstance->GetLcgRandom());
-            }
-            else
-            {
-                uniqueData->m_countDownTime = MCore::Random::RandF(m_minRandomTime, m_maxRandomTime);
-            }
+            uniqueData->m_countDownTime =
+                m_minRandomTime + (m_maxRandomTime - m_minRandomTime) * animGraphInstance->GetLcgRandom().GetRandomFloat();
         }
         else
         {
diff --git a/Gems/EMotionFX/Code/MCore/Source/Random.h b/Gems/EMotionFX/Code/MCore/Source/Random.h
index 55576bb958..d2454af38b 100644
--- a/Gems/EMotionFX/Code/MCore/Source/Random.h
+++ b/Gems/EMotionFX/Code/MCore/Source/Random.h
@@ -64,22 +64,6 @@ namespace MCore
          */
         static MCORE_INLINE float RandF(float minVal, float maxVal)                                 { return minVal + (maxVal - minVal) * rand() / (float)RAND_MAX; }
 
-        /**
-        * Generate a uniform random float in a range of a given minimum and maximum.
-        * @param minVal The minimum value of the range.
-        * @param maxVal The maximum value of the range.
-        * @result A uniform random floating point number in range of [min..max].
-        */
-        static MCORE_INLINE float RandF(float minVal, float maxVal, unsigned int seed) { AZ_UNUSED(seed); return minVal + (maxVal - minVal) * rand() / (float)RAND_MAX; }
-
-        /**
-        * Generate a uniform random float in a range of a given minimum and maximum.
-        * @param minVal The minimum value of the range.
-        * @param maxVal The maximum value of the range.
-        * @result A uniform random floating point number in range of [min..max].
-        */
-        static MCORE_INLINE float RandF(float minVal, float maxVal, LcgRandom& rand) { return minVal + (maxVal - minVal) * rand.GetRandomFloat(); }
-
         /**
          * Generates a uniform random normalized direction vector, using floats.
          * @result A uniform random direction vector with a length of 1.