Perf: Prevent pipeline from aging scene after timeline finishes

src/Rendering/Interfaces/IRenderStateAssembler.cs

@@ -30,10 +30,11 @@ RenderState Assemble(
         PlayerDiagnostics diagnostics,
         SceneNode? hoveredNode,
         HoveredPodHud? hoveredPod,
-        LayoutMode mode);
+        LayoutMode mode,
+        bool sceneUnchanged = false);
 
     /// <summary>
     /// Clears accumulated internal state.
     /// </summary>
     void Reset();
-}
+}

src/Rendering/Pipeline/RenderEventBuffer.cs

@@ -15,6 +15,7 @@ internal sealed class RenderEventBuffer(RenderEventKinds renderEvents) : IDispos
         renderEvents);
 
     private RenderEventKinds _renderEvents = renderEvents;
+    private bool _hasBufferedEvents;
 
     /// <summary>
     /// Updates enabled render event kinds and resets aggregation state.
@@ -46,17 +47,21 @@ public void Add(
         {
             _aggregation.Process(
                 evt);
+            _hasBufferedEvents = true;
         }
     }
 
     /// <summary>
     /// Flushes buffered events into the rendering pipeline.
     /// </summary>
-    public void FlushTo(
+    public bool FlushTo(
         RenderingPipeline pipeline)
     {
         lock (_sync)
         {
+            if (!_hasBufferedEvents)
+                return false;
+
             _aggregation.Flush();
 
             foreach (var t in RenderEventDispatchTable.Table)
@@ -72,6 +77,8 @@ public void FlushTo(
             }
 
             _aggregation.Clear();
+            _hasBufferedEvents = false;
+            return true;
         }
     }
 
@@ -85,4 +92,4 @@ public void Dispose()
             _aggregation.Dispose();
         }
     }
-}
+}

src/Rendering/Pipeline/RenderFrameAssembler.cs

@@ -25,7 +25,8 @@ public void SubmitFrame(
         PlayerDiagnostics diagnostics,
         SceneNode? hoveredNode,
         HoveredPodHud? hoveredPod,
-        LayoutMode layoutMode)
+        LayoutMode layoutMode,
+        bool sceneUnchanged = false)
     {
         var state =
             assembler.Assemble(
@@ -38,9 +39,10 @@ public void SubmitFrame(
                 diagnostics,
                 hoveredNode,
                 hoveredPod,
-                layoutMode);
+                layoutMode,
+                sceneUnchanged);
 
         output.Submit(
             state);
     }
-}
+}

src/Rendering/Pipeline/RenderingPipeline.cs

@@ -146,23 +146,27 @@ internal void OnProgress(
             ClearSceneState();
         }
 
-        _events.FlushTo(
-            this);
+        var hadNewEvents =
+            _events.FlushTo(
+                this);
 
-        UpdateFrame();
+        UpdateFrame(
+            hadNewEvents);
     }
 
     /// <summary>
     /// Updates simulation, hover state, diagnostics, and frame output.
     /// </summary>
-    private void UpdateFrame()
+    private void UpdateFrame(
+        bool hadNewEvents)
     {
         var diagnostics =
             Player.GetDiagnostics();
 
         float dt =
             _frameUpdater.Tick(
-                diagnostics);
+                diagnostics,
+                hadNewEvents);
 
         _hover.Tick();
 
@@ -183,7 +187,8 @@ private void UpdateFrame()
             diagnostics,
             _hover.HoveredNode,
             _hover.HoveredPod,
-            _options.Mode);
+            _options.Mode,
+            sceneUnchanged: !hadNewEvents && dt == 0f);
     }
 
     /// <summary>

src/Rendering/Pipeline/SceneFrameUpdater.cs

@@ -22,14 +22,16 @@ internal sealed class SceneFrameUpdater(
     /// Ticks all frame-level scene systems and returns clamped delta time.
     /// </summary>
     public float Tick(
-        PlayerDiagnostics diagnostics)
+        PlayerDiagnostics diagnostics,
+        bool hadNewEvents = false)
     {
         float dt = CalculateDeltaTime(
             diagnostics);
 
         StepLayout(
             diagnostics,
-            dt);
+            dt,
+            hadNewEvents);
 
         anim.Tick(
             dt);
@@ -68,7 +70,8 @@ private float CalculateDeltaTime(
             currentWallTime;
 
         if (diagnostics.State == PlayerState.Idle ||
-            diagnostics.State == PlayerState.Paused)
+            diagnostics.State == PlayerState.Paused ||
+            diagnostics.State == PlayerState.Finished)
         {
             return 0f;
         }
@@ -83,11 +86,18 @@ private float CalculateDeltaTime(
     /// </summary>
     private void StepLayout(
         PlayerDiagnostics diagnostics,
-        float dt)
+        float dt,
+        bool hadNewEvents)
     {
         if (dt <= 0f)
             return;
 
+        if (!hadNewEvents &&
+            layout.Energy <= 0f)
+        {
+            return;
+        }
+
         float speedBoost =
             (float)Math.Max(
                 1.0,
@@ -126,4 +136,4 @@ private void StepLayout(
     /// </summary>
     public void ResetTime() =>
         _lastWallTime = 0;
-}
+}

src/Rendering/States/Hud/ExtensionStatisticsAssembler.cs

@@ -9,11 +9,18 @@ namespace ChangeTrace.Rendering.States.Hud;
 /// </summary>
 internal sealed class ExtensionStatisticsAssembler
 {
+    private IReadOnlyList<ExtensionStat> _cached = [];
+
     /// <summary>
     /// Collects and ranks the most common file extensions in the scene.
     /// </summary>
-    public IReadOnlyList<ExtensionStat> Assemble(ISceneGraph scene)
+    public IReadOnlyList<ExtensionStat> Assemble(
+        ISceneGraph scene,
+        bool sceneUnchanged)
     {
+        if (sceneUnchanged)
+            return _cached;
+
         var counts = new Dictionary<string, int>();
 
         foreach (var node in scene.Nodes.Values)
@@ -28,10 +35,15 @@ public IReadOnlyList<ExtensionStat> Assemble(ISceneGraph scene)
                 counts.GetValueOrDefault(node.Extension) + 1;
         }
 
-        return counts
+        _cached = counts
             .OrderByDescending(x => x.Value)
             .Take(8)
             .Select(x => new ExtensionStat(x.Key, x.Value))
             .ToList();
+
+        return _cached;
     }
-}
+
+    public void Reset() =>
+        _cached = [];
+}

src/Rendering/States/RenderStateAssembler.cs

@@ -29,6 +29,9 @@ internal sealed class RenderStateAssembler : IRenderStateAssembler
     private readonly LeaderboardAssembler _leaderboard = new();
     private readonly HudStateAssembler _hud = new();
 
+    private ISceneSnapshot _cachedSceneSnapshot = SceneSnapshot.Empty;
+    private bool _hasCachedSceneSnapshot;
+
     /// <summary>
     /// Records contributor activity for leaderboard tracking.
     /// </summary>
@@ -39,7 +42,15 @@ public void RecordActorEvent(string actor, string commitSha) =>
     /// Clears accumulated render-related state.
     /// </summary>
     public void Reset() =>
+        ResetCaches();
+
+    private void ResetCaches()
+    {
         _leaderboard.Reset();
+        _extensions.Reset();
+        _cachedSceneSnapshot = SceneSnapshot.Empty;
+        _hasCachedSceneSnapshot = false;
+    }
 
     private static Dictionary<string, int> BuildNodeIndex(
         IReadOnlyList<NodeSnapshot> nodes)
@@ -65,14 +76,15 @@ public RenderState Assemble(
         PlayerDiagnostics diagnostics,
         SceneNode? hoveredNode,
         HoveredPodHud? hoveredPod,
-        LayoutMode layoutMode)
+        LayoutMode layoutMode,
+        bool sceneUnchanged = false)
     {
-        var nodeSnapshots = _nodes.Assemble(scene.Nodes);
-        var nodeIndex = BuildNodeIndex(nodeSnapshots);
-        var avatarSnapshots = _avatars.Assemble(scene.Avatars, out var activeAvatarsCount);
-        var edgeSnapshots = _edges.Assemble(scene, nodeIndex);
-        var particleSnapshots = _particles.Assemble(animationSystem);
-        var extensions = _extensions.Assemble(scene);
+        int activeAvatarsCount =
+            scene.Avatars.Count(static avatar => avatar.Value.ActivityLevel > 0.1f);
+
+        var extensions = _extensions.Assemble(
+            scene,
+            sceneUnchanged);
         var leaderboard = _leaderboard.Assemble();
 
         var hudState =
@@ -88,11 +100,10 @@ public RenderState Assemble(
                 leaderboard);
 
         var sceneSnapshot =
-            SceneSnapshotMaterializer.Create(
-                nodeSnapshots,
-                avatarSnapshots,
-                edgeSnapshots,
-                particleSnapshots);
+            GetOrCreateSceneSnapshot(
+                scene,
+                animationSystem,
+                sceneUnchanged);
 
         return new RenderState(
             virtualTime,
@@ -103,4 +114,29 @@ public RenderState Assemble(
             layoutMode,
             diagnostics.ManagedMemoryMb);
     }
+
+    private ISceneSnapshot GetOrCreateSceneSnapshot(
+        ISceneGraph scene,
+        IAnimationSystem animationSystem,
+        bool sceneUnchanged)
+    {
+        if (sceneUnchanged && _hasCachedSceneSnapshot)
+            return _cachedSceneSnapshot;
+
+        var nodeSnapshots = _nodes.Assemble(scene.Nodes);
+        var nodeIndex = BuildNodeIndex(nodeSnapshots);
+        var avatarSnapshots = _avatars.Assemble(scene.Avatars, out _);
+        var edgeSnapshots = _edges.Assemble(scene, nodeIndex);
+        var particleSnapshots = _particles.Assemble(animationSystem);
+
+        _cachedSceneSnapshot =
+            SceneSnapshotMaterializer.Create(
+                nodeSnapshots,
+                avatarSnapshots,
+                edgeSnapshots,
+                particleSnapshots);
+
+        _hasCachedSceneSnapshot = true;
+        return _cachedSceneSnapshot;
+    }
 }