Gimbal lock fix for spline meshes

Author: Nebukam

Content/Assets/Debug/LV_Debug.umap

@@ -354,6 +354,8 @@ namespace PCGExPathSplineMesh
 			Segment.Params.StartTangent = LeaveReader->Read(Index);
 			Segment.Params.EndTangent = ArriveReader->Read(NextIndex);
 		}
+
+		if (Settings->bFixGimbalLock) { Segment.FixGimbalLock(); }
 	}
 
 	void FProcessor::CompleteWork()

Content/Assets/Debug/Misc/BP_ActorWithSpline.uasset

@@ -256,6 +256,8 @@ namespace PCGExPathSplineMeshSimple
 			Segment.Params.StartTangent = LeaveReader->Read(Index);
 			Segment.Params.EndTangent = ArriveReader->Read(NextIndex);
 		}
+
+		if (Settings->bFixGimbalLock) { Segment.FixGimbalLock(); }
 	}
 
 	void FProcessor::CompleteWork()

Content/Assets/Debug/Misc/PCG_SplineTest.uasset

@@ -72,14 +72,6 @@ class /*PCGEXTENDEDTOOLKIT_API*/ UPCGExPathSplineMeshSettings : public UPCGExPat
 	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "Settings|Distribution", meta=(PCG_Overridable))
 	FName AssetPathAttributeName = "AssetPath";
 
-	/**  */
-	//UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "Settings|Target Actor", meta = (PCG_Overridable))
-	//bool bPerSegmentTargetActor = false;
-
-	/**  */
-	//UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "Settings|Target Actor", meta=(PCG_Overridable, EditCondition="bPerSegmentTargetActor", EditConditionHides))
-	//FName TargetActorAttributeName;
-
 	/** Whether to read tangents from attributes or not. */
 	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Settings, meta = (PCG_Overridable))
 	bool bApplyCustomTangents = false;
@@ -119,6 +111,10 @@ class /*PCGEXTENDEDTOOLKIT_API*/ UPCGExPathSplineMeshSettings : public UPCGExPat
 	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "Settings|Additional Outputs", meta=(PCG_Overridable, EditCondition="WeightToAttribute!=EPCGExWeightOutputMode::NoOutput && WeightToAttribute!=EPCGExWeightOutputMode::NormalizedToDensity && WeightToAttribute!=EPCGExWeightOutputMode::NormalizedInvertedToDensity"))
 	FName WeightAttributeName = "AssetWeight";
 
+	/** Fix gimbal lock, a.k.a weirdly twisted mesh */
+	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Settings, meta=(PCG_Overridable, DisplayName="Fix Gimbal Lock"))
+	bool bFixGimbalLock = false;
+	
 	/** Default static mesh config applied to spline mesh components. */
 	UPROPERTY(EditAnywhere, Category = Settings)
 	FPCGExStaticMeshComponentDescriptor DefaultDescriptor;

Content/Assets/Debug/Misc/PCG_Tensor.uasset

@@ -91,6 +91,10 @@ class /*PCGEXTENDEDTOOLKIT_API*/ UPCGExPathSplineMeshSimpleSettings : public UPC
 	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Settings, meta=(PCG_Overridable, DisplayName="End Offset", EditCondition="EndOffsetInput==EPCGExInputValueType::Constant", EditConditionHides))
 	FVector2D EndOffset = FVector2D::ZeroVector;
 
+	/** Fix gimbal lock, a.k.a weirdly twisted mesh */
+	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Settings, meta=(PCG_Overridable, DisplayName="Fix Gimbal Lock"))
+	bool bFixGimbalLock = false;
+	
 	/**  */
 	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = Settings, meta=(PCG_Overridable))
 	EPCGExMinimalAxis SplineMeshAxisConstant = EPCGExMinimalAxis::X;

Plugins/PCGExtendedToolkit/Source/PCGExtendedToolkit/Private/Paths/PCGExPathSplineMesh.cpp

@@ -300,6 +300,16 @@ namespace PCGExPaths
 		const FPCGExMeshCollectionEntry* MeshEntry = nullptr;
 		FSplineMeshParams Params;
 
+		void FixGimbalLock()
+		{
+			// Thanks Drakynfly @ https://www.reddit.com/r/unrealengine/comments/kqo6ez/usplinecomponent_twists_in_on_itself/
+
+			const FVector NormalA = Params.StartTangent.GetSafeNormal(0.001);
+			const FVector NormalB = Params.EndTangent.GetSafeNormal(0.001);
+			if (const float Dot = NormalA | NormalB; Dot > 0.99 || Dot <= -0.99) { UpVector = NormalA; }
+			else { UpVector = NormalA ^ NormalB; }
+		}
+
 		void ApplySettings(USplineMeshComponent* Component) const
 		{
 			check(Component)
@@ -315,7 +325,7 @@ namespace PCGExPaths
 			else { Component->SetEndRoll(Params.EndRoll, false); }
 
 			Component->SetForwardAxis(SplineMeshAxis, false);
-			Component->SetSplineUpDir(FVector::UpVector, false);
+			Component->SetSplineUpDir(UpVector, false);
 
 			Component->SetStartOffset(Params.StartOffset, false);
 			Component->SetEndOffset(Params.EndOffset, false);