Move particles along surface (along U coordinate)

[Digi]

Hi!

I like to spawn particles at the start of a surface and move them along the surface following the U-coordinate of the surface.
See image attached - the particles shall follow that helix.

I tried different approaches.
I used a Mapping operator to give particles the corresponding U coordinate of the surface, but I can't animate that.
I tried it with a script controller with help of ChatGPT, but there is always something in the script which the script controller doesn't know)

I searched for a way inside a speed operator to use surface coordinates as direction, but couldn't find.

I tried with a path follow instead, but I never can find good values so that particles really follow a path accurately.

Can someone tell me how that is possible??



Here is one of the scripts I tried. (But in this one, "particles" wasn't known to the script controller)


public void SimulationStep()

{
    float speed = 0.2f;

    foreach (var p in particles)
    {
        Vector2 uv = p.MappingOverride;

        uv.X += speed * tpf;  // tpf = time per frame

        if (uv.X > 1.0f)
            uv.X = 0.0f;

        p.MappingOverride = uv;

        p.Position = p.GetPositionFromMap(1, uv);
    }
}