I think 'reserved for possible future use' is the correct answer.
As I recall, VertexW doesn't really return anything useful. It just gives a standard value of 1.
This is analogous to ReadPixel in 2D graphics. It tells you the alpha value is 255 ( fully opaque ) even though there really is no alpha support.
As I recall, VertexW doesn't really return anything useful. It just gives a standard value of 1.
This is analogous to ReadPixel in 2D graphics. It tells you the alpha value is 255 ( fully opaque ) even though there really is no alpha support.