public TerrainLayerSmoothnessSource smoothnessSource { get; set; }

Used for choosing where smoothness value comes from when _diffuseTexture has an alpha channel. Setting to TerrainLayerSmoothnessSource.ConstantMultipliedByDiffuseAlpha results in using a mix of the smoothness value set in _smoothness and of the _diffuseTexture alpha channel. Setting to TerrainLayerSmoothnessSource.DiffuseAlphaChannel results in using the smoothness value set from the alpha channel of _diffuseTexture. Setting to TerrainLayerSmoothnessSource.ConstantOnly results in using the smoothness value set in _smoothness.