I included a shader to calculate per Vertex Normals based on the triangle. After adding it as Effect (toEffect Shaders.mkNormals), I get an error message after startup: "System.Exception: '[FShade] cannot add output "PhaseDistances" to GeometryShader since no SourceVertexIndex was available'"

  let mkNormals (tri : Triangle<Effects.Vertex>) =
    triangle {
      let a = tri.P1.wp.XYZ - tri.P0.wp.XYZ
      let b = tri.P2.wp.XYZ - tri.P0.wp.XYZ
      let n = V3d.Cross(a,b)
      yield {tri.P0 with n = n}
      yield {tri.P1 with n = n}
      yield {tri.P2 with n = n}
  }