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

Development Programming & Scripting C++
1

Vertex positions of static mesh component can be calculated by applying component’s transform to position buffer of static mesh (as showed and explained in this thread: Accessing Vertex Positions of static mesh - C++ Gameplay Programming - Unreal Engine Forums).

Do I have to manually apply spline transformations to vertices of a static mesh or world positions are stored somewhere?

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

3 Likes
3

Hi AlekseyIlin,

do you have any idea about how to do this using blueprints ?

4

Alright, just found it :slight_smile:
With “get end position” and “Transform Location” nodes, I get the world location of the end point of my spline mesh component.

5

Hi Alekseyllin:

Is there still some code on github floating around, in regards to how to do this? Thanks

6

Thank you for this solution. I got a plugin out called Runtime Vertex Color Paint & Detection Plugin and thanks to you it now supports spline mesh components as well :slight_smile:

I’ll gladly give you a copy of the plugin as a thank you! If you want it you can just send me the epic email account that should get it and i’ll hook you up :wink:

All the Best,
Alex.