How to get vertex positions of spline mesh component in world space?

Development Programming & Scripting C++
2

Figured out how to convert vertex poistions from asset (static mesh) to spline. The following method is used in StaticMesh.cpp, in function static void GetStaticLightingVertex (https://github.com/EpicGames/UnrealEngine/blob/76085d1106078d8988e4404391428252ba1eb9a7/Engine/Source/Programs/UnrealLightmass/Private/Lighting/StaticMesh.cpp#L151) and also in vertex shader for spline meshes

this function transforms position in static mesh space to spline mesh space:



FVector StaticMeshToSplineMeshVertexPosition(const FVector& StaticMeshVertexPosition, USplineMeshComponent* SplineMeshComponent)
{
	const float VertexPositionAlongSpline = StaticMeshVertexPosition[SplineMeshComponent->ForwardAxis];
	const FTransform StaticMeshToSplineMeshTransform = SplineMeshComponent->CalcSliceTransform(VertexPositionAlongSpline);
	FVector SlicePos = StaticMeshVertexPosition;
	SlicePos[SplineMeshComponent->ForwardAxis] = 0;
	const FVector SplineMeshSpaceVector = StaticMeshToSplineMeshTransform.TransformPosition(SlicePos);
	FVector ResultPos = SplineMeshSpaceVector;
	return SplineMeshSpaceVector;
}

this code gets positions of all vertices of USplineMeshComponent in world space:



UStaticMesh* StaticMesh = SplineMeshComponent->GetStaticMesh();

const FStaticMeshLODResources& RenderData = StaticMesh->RenderData->LODResources[0];
for (uint32 Index = 0; Index < RenderData.PositionVertexBuffer.GetNumVertices(); Index++)
{
	const FVector StaticMeshSpacePosition = RenderData.PositionVertexBuffer.VertexPosition(Index);
	const FVector SplineMeshSpacePosition = StaticMeshToSplineMeshVertexPosition(StaticMeshSpacePosition, SplineMeshComponent);
	const FVector WorldSpacePosition = SplineMeshComponent->GetComponentLocation() + SplineMeshComponent->GetComponentTransform().TransformVector(SplineMeshSpacePosition);

}

I still have no idea why you have to do this


 SlicePos[SplineMeshComponent->ForwardAxis] = 0;

but it works

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