Merge pull request #117 from Unity-Technologies/fixed-random-seed-from-index

Fixed GenerateRandomSeedFromIndex method

com.unity.perception/CHANGELOG.md

 Expanded all Unity Simulation references from USim to Unity Simulation
 Uniform and Normal samplers now serialize their random seeds
 
+The ScenarioBase's GenerateIterativeRandomSeed() method has been renamed to GenerateRandomSeedFromIndex()
+
 ### Deprecated
 
 ### Removed
 Fixed Unity Simulation nodes generating one extra empty image before generating their share of the randomization scenario iterations
 
 Fixed enumeration in the CategoricalParameter.categories property
+
+The GenerateRandomSeedFromIndex method now correctly hashes the current scenario iteration into the random seed it generates
 
 ## [0.5.0-preview.1] - 2020-10-14
 

com.unity.perception/Runtime/Randomization/Randomizers/RandomizerExamples/Randomizers/BackgroundObjectPlacementRandomizer.cs

 
             for (var i = 0; i < layerCount; i++)
             {
-                var seed = scenario.GenerateIterativeRandomSeed(i);
+                var seed = scenario.GenerateRandomSeedFromIndex(i);
                 var placementSamples = PoissonDiskSampling.GenerateSamples(
                     placementArea.x, placementArea.y, separationDistance, seed);
                 var offset = new Vector3(placementArea.x, placementArea.y, 0f) * -0.5f;

com.unity.perception/Runtime/Randomization/Scenarios/ScenarioBase.cs

         }
 
         /// <summary>
-        /// Generates a random seed by hashing three values together: an arbitrary iteration value,
-        /// the current scenario iteration, and a base random seed
+        /// Generates a random seed by hashing three values together: an arbitrary index value,
+        /// the current scenario iteration, and a base random seed. This method is useful for deterministically
+        /// generating random seeds from within a for-loop.
-        public uint GenerateIterativeRandomSeed(int iteration, uint baseSeed = SamplerUtility.largePrime)
+        public uint GenerateRandomSeedFromIndex(int iteration, uint baseSeed = SamplerUtility.largePrime)
-            return SamplerUtility.IterateSeed((uint)iteration, baseSeed);
+            var seed =  SamplerUtility.IterateSeed((uint)iteration, baseSeed);
+            return SamplerUtility.IterateSeed((uint)currentIteration, seed);
         }
 
         void ValidateParameters()

com.unity.perception/Tests/Runtime/Randomization/ScenarioTests.cs

             Assert.AreEqual(DatasetCapture.SimulationState.SequenceTime, 0);
         }
 
+        [UnityTest]
+        public IEnumerator GeneratedRandomSeedsChangeWithScenarioIteration()
+        {
+            yield return CreateNewScenario(3, 1);
+            var seed = m_Scenario.GenerateRandomSeed();
+            var seeds = new uint[3];
+            for (var i = 0; i < 3; i++)
+                seeds[i] = m_Scenario.GenerateRandomSeedFromIndex(i);
+
+            yield return null;
+            Assert.AreNotEqual(seed, m_Scenario.GenerateRandomSeed());
+            for (var i = 0; i < 3; i++)
+                Assert.AreNotEqual(seeds[i], m_Scenario.GenerateRandomSeedFromIndex(i));
+        }
+
         PerceptionCamera SetupPerceptionCamera()
         {
             m_TestObject.SetActive(false);