Settings tweaks for better performance

Config/DefaultEngine.ini

@@ -165,6 +165,7 @@ r.Lumen.Reflections.HardwareRayTracing.Translucent.Refraction.EnableForProject=F
 r.Streaming.PoolSize=2048
 
 r.Shadow.CSMCaching=True
+r.Shadow.RadiusThreshold=0.04
 r.Nanite.ProjectEnabled=False
 r.Nanite=False
 
@@ -194,6 +195,8 @@ r.VolumetricCloud.ViewRaySampleMaxCount=64
 
 r.DistanceFieldAO=0
 r.DistanceFieldShadowing=0
+r.AmbientOcclusionLevels=1
+r.Shadow.CSMCaching=0
 
 [/Script/LinuxTargetPlatform.LinuxTargetSettings]
 TargetArchitecture=X86_64UnknownLinuxGnu

Source/ProjectEleri/Private/TimeOfDayManager.cpp

@@ -297,12 +297,28 @@ void ATimeOfDayManager::RotateSun(const float &_rotator)
 {
     if (!enableTimeOfDay)
         return;
+    if (!CurrentWeatherPreset || !CurrentWeatherPreset->SunRotationCurve)
+        return;
     if (sunLight->IsValidLowLevel())
     {
         FVector currentRotInVectors = FVector(0.0f, CurrentWeatherPreset->SunRotationCurve->GetFloatValue(FloatMinutes),
                                               110.0f);
         FRotator currentSunRotation = FRotator(FRotator::MakeFromEuler(currentRotInVectors));
+
+        // The renderer only reuses its cached CSM shadow maps while the light matrix is bit-identical (the
+        // cached shadow initializer is compared with == in the shadow setup), so re-orienting the light every
+        // frame throws the whole cascade shadow map cache away every frame. Only move the light once the sun
+        // actually travelled far enough to be worth the cache rebuild.
+        const float PitchDelta = FMath::Abs(FMath::FindDeltaAngleDegrees(AppliedSunRotation.Pitch, currentSunRotation.Pitch));
+        const float YawDelta = FMath::Abs(FMath::FindDeltaAngleDegrees(AppliedSunRotation.Yaw, currentSunRotation.Yaw));
+
+        if (bSunRotationDirty || SunRotationUpdateThreshold <= 0.0f || PitchDelta >= SunRotationUpdateThreshold ||
+            YawDelta >= SunRotationUpdateThreshold)
+        {
             sunLight->SetWorldRotation(currentSunRotation);
+            AppliedSunRotation = currentSunRotation;
+            bSunRotationDirty = false;
+        }
     }
 }
 

Source/ProjectEleri/Public/TimeOfDayManager.h

@@ -205,12 +205,29 @@ public:
     UPROPERTY(EditAnywhere, Category = "Time of Day - Lightning Setting")
     float daySpeed = 10.0f;
 
+    /** Minimum movement of the sun in degrees before the directional light is actually re-oriented.
+     *  The renderer only reuses its cached CSM shadow maps while the light matrix is completely unchanged
+     *  (the cached shadow initializer is compared with == in the shadow setup), so writing the light
+     *  transform every frame invalidates and releases the whole cascade shadow map cache every frame.
+     *  The light is re-oriented roughly every (SunRotationUpdateThreshold / sun degrees per second) seconds,
+     *  so the cache is reused for all the frames in between. 0 disables the throttle. */
+    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Time of Day - Lightning Setting")
+    float SunRotationUpdateThreshold = 0.1f;
+
     UPROPERTY(EditAnywhere, Category = "Time of Day - Lightning Setting")
     FLinearColor SubsurfaceColorDay;
 
     UPROPERTY(VisibleAnywhere, Category = "Time of Day - Info")
     float rotator;
 
+    /** Rotation that is currently applied to sunLight, used to throttle the per-frame SetWorldRotation. */
+    UPROPERTY(VisibleAnywhere, Category = "Time of Day - Info")
+    FRotator AppliedSunRotation;
+
+    /** True until the current sun rotation has been pushed into the light at least once. */
+    UPROPERTY(VisibleAnywhere, Category = "Time of Day - Info")
+    bool bSunRotationDirty = true;
+
     UPROPERTY(VisibleAnywhere, Category = "Time of Day - Info")
     float CurrentWeaterFadeAlpha;