Fixed potential render scene time precision issues.

The timestamp was simply converted from GetTimeAtCurrentTick to a float. Since this value is backed by QueryPerformanceCounter which is 0 at boot, you could see broken animations on the GPU when your system has been on for a long time. So I simplified the RPI's time API (removed unused code), and subtracted the application start time each frame before converting the time value to a float.
Also moved FindShaderInputConstantIndex("m_time") to be called only once, instead of every frame.

Signed-off-by: santorac <55155825+santorac@users.noreply.github.com>

Gems/Atom/RPI/Code/Include/Atom/RPI.Public/RPISystem.h

@@ -96,8 +96,7 @@ namespace AZ
             // SystemTickBus::OnTick
             void OnSystemTick() override;
 
-            // Fill system time and game time information for simulation or rendering
-            void FillTickTimeInfo();
+            float GetCurrentTime();
 
             // The set of core asset handlers registered by the system.
             AZStd::vector<AZStd::unique_ptr<Data::AssetHandler>> m_assetHandlers;
@@ -123,8 +122,9 @@ namespace AZ
             // The job policy used for feature processor's rendering prepare
             RHI::JobPolicy m_prepareRenderJobPolicy = RHI::JobPolicy::Parallel;
 
-            TickTimeInfo m_tickTime;
-
+            ScriptTimePoint m_startTime;
+			float m_currentSimulationTime = 0.0f;
+			
             RPISystemDescriptor m_descriptor;
 
             // Reference to the shader asset that is used

Gems/Atom/RPI/Code/Include/Atom/RPI.Public/RenderPipeline.h

@@ -32,7 +32,6 @@ namespace AZ
     namespace RPI
     {
         class Scene;
-        struct TickTimeInfo;
         class ShaderResourceGroup;
         class AnyAsset;
         class WindowContext;
@@ -203,7 +202,7 @@ namespace AZ
             void OnRemovedFromScene(Scene* scene);
 
             // Called when this pipeline is about to be rendered
-            void OnStartFrame(const TickTimeInfo& tick);
+            void OnStartFrame(float time);
 
             // Called when the rendering of current frame is finished.
             void OnFrameEnd();

Gems/Atom/RPI/Code/Include/Atom/RPI.Public/Scene.h

@@ -47,14 +47,6 @@ namespace AZ
         // Callback function to modify values of a ShaderResourceGroup
         using ShaderResourceGroupCallback = AZStd::function<void(ShaderResourceGroup*)>;
 
-        //! A structure for ticks which contains system time and game time.
-        struct TickTimeInfo
-        {
-            float m_currentGameTime;
-            float m_gameDeltaTime = 0;
-        };
-
-
         class Scene final
             : public SceneRequestBus::Handler
         {
@@ -173,12 +165,14 @@ namespace AZ
                         
             // Cpu simulation which runs all active FeatureProcessor Simulate() functions.
             // @param jobPolicy if it's JobPolicy::Parallel, the function will spawn a job thread for each FeatureProcessor's simulation.
-            void Simulate(const TickTimeInfo& tickInfo, RHI::JobPolicy jobPolicy);
+            // @param simulationTime the number of seconds since the application started
+            void Simulate(RHI::JobPolicy jobPolicy, float simulationTime);
 
             // Collect DrawPackets from FeatureProcessors
             // @param jobPolicy if it's JobPolicy::Parallel, the function will spawn a job thread for each FeatureProcessor's
             // PrepareRender.
-            void PrepareRender(const TickTimeInfo& tickInfo, RHI::JobPolicy jobPolicy);
+            // @param simulationTime the number of seconds since the application started; this is the same time value that was passed to Simulate()
+            void PrepareRender(RHI::JobPolicy jobPolicy, float simulationTime);
 
             // Function called when the current frame is finished rendering.
             void OnFrameEnd();
@@ -240,6 +234,7 @@ namespace AZ
             // Registry which allocates draw filter tag for RenderPipeline
             RHI::Ptr<RHI::DrawFilterTagRegistry> m_drawFilterTagRegistry;
 
+            RHI::ShaderInputConstantIndex m_timeInputIndex;
             float m_simulationTime;
         };
 

Gems/Atom/RPI/Code/Source/RPI.Public/RPISystem.cpp

@@ -249,23 +249,25 @@ namespace AZ
 
             AssetInitBus::Broadcast(&AssetInitBus::Events::PostLoadInit);
 
-            // Update tick time info
-            FillTickTimeInfo();
+            m_currentSimulationTime = GetCurrentTime();
 
             for (auto& scene : m_scenes)
             {
-                scene->Simulate(m_tickTime, m_simulationJobPolicy);
+                scene->Simulate(m_simulationJobPolicy, m_currentSimulationTime);
             }
         }
 
-        void RPISystem::FillTickTimeInfo()
+        float RPISystem::GetCurrentTime()
         {
-            AZ::TickRequestBus::BroadcastResult(m_tickTime.m_gameDeltaTime, &AZ::TickRequestBus::Events::GetTickDeltaTime);
-            ScriptTimePoint currentTime;
-            AZ::TickRequestBus::BroadcastResult(currentTime, &AZ::TickRequestBus::Events::GetTimeAtCurrentTick);
-            m_tickTime.m_currentGameTime = static_cast<float>(currentTime.GetMilliseconds());
-        }
+            ScriptTimePoint timeAtCurrentTick;
+            AZ::TickRequestBus::BroadcastResult(timeAtCurrentTick, &AZ::TickRequestBus::Events::GetTimeAtCurrentTick);
+
+            // We subtract the start time to maximize precision of the time value, since we will be converting it to a float.
+            double currentTime = timeAtCurrentTick.GetSeconds() - m_startTime.GetSeconds();
 
+            return aznumeric_cast<float>(currentTime);
+        }
+		
         void RPISystem::RenderTick()
         {
             if (!m_systemAssetsInitialized)
@@ -282,7 +284,7 @@ namespace AZ
             // [GFX TODO] We may parallel scenes' prepare render.
             for (auto& scenePtr : m_scenes)
             {
-                scenePtr->PrepareRender(m_tickTime, m_prepareRenderJobPolicy);
+                scenePtr->PrepareRender(m_prepareRenderJobPolicy, m_currentSimulationTime);
             }
 
             m_rhiSystem.FrameUpdate(

Gems/Atom/RPI/Code/Source/RPI.Public/RenderPipeline.cpp

@@ -375,11 +375,11 @@ namespace AZ
             m_scene->RemoveRenderPipeline(m_nameId);
         }
 
-        void RenderPipeline::OnStartFrame(const TickTimeInfo& tick)
+        void RenderPipeline::OnStartFrame(float time)
         {
             AZ_PROFILE_SCOPE(RPI, "RenderPipeline: OnStartFrame");
 
-            m_lastRenderStartTime = tick.m_currentGameTime;
+            m_lastRenderStartTime = time;
 
             OnPassModified();
 

Gems/Atom/RPI/Code/Source/RPI.Public/Scene.cpp

@@ -42,6 +42,9 @@ namespace AZ
             {
                 auto shaderAsset = RPISystemInterface::Get()->GetCommonShaderAssetForSrgs();
                 scene->m_srg = ShaderResourceGroup::Create(shaderAsset, sceneSrgLayout->GetName());
+                
+                // Set value for constants defined in SceneTimeSrg.azsli
+                scene->m_timeInputIndex = scene->m_srg->FindShaderInputConstantIndex(Name{ "m_time" });
             }
             
             return ScenePtr(scene);
@@ -346,11 +349,11 @@ namespace AZ
             return nullptr;
         }
 
-        void Scene::Simulate([[maybe_unused]] const TickTimeInfo& tickInfo, RHI::JobPolicy jobPolicy)
+        void Scene::Simulate(RHI::JobPolicy jobPolicy, float simulationTime)
         {
             AZ_PROFILE_SCOPE(RPI, "Scene: Simulate");
 
-            m_simulationTime = tickInfo.m_currentGameTime;
+            m_simulationTime = simulationTime;
 
             // If previous simulation job wasn't done, wait for it to finish.
             WaitAndCleanCompletionJob(m_simulationCompletion);
@@ -404,11 +407,9 @@ namespace AZ
         {
             if (m_srg)
             {
-                // Set value for constants defined in SceneTimeSrg.azsli
-                RHI::ShaderInputConstantIndex timeIndex = m_srg->FindShaderInputConstantIndex(Name{ "m_time" });
-                if (timeIndex.IsValid())
+                if (m_timeInputIndex.IsValid())
                 {
-                    m_srg->SetConstant(timeIndex, m_simulationTime);
+                    m_srg->SetConstant(m_timeInputIndex, m_simulationTime);
                 }
 
                 // signal any handlers to update values for their partial scene srg
@@ -418,7 +419,7 @@ namespace AZ
             }
         }
 
-        void Scene::PrepareRender(const TickTimeInfo& tickInfo, RHI::JobPolicy jobPolicy)
+        void Scene::PrepareRender(RHI::JobPolicy jobPolicy, float simulationTime)
         {
             AZ_PROFILE_SCOPE(RPI, "Scene: PrepareRender");
 
@@ -438,7 +439,7 @@ namespace AZ
                     if (pipeline->NeedsRender())
                     {
                         activePipelines.push_back(pipeline);
-                        pipeline->OnStartFrame(tickInfo);
+                        pipeline->OnStartFrame(simulationTime);
                     }
                 }
             }