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-- |
-- Module      :  Graphics.FieldTrip.Vertex
-- Copyright   :  (c) Conal Elliott 2008
-- License     :  BSD3
-- 
-- Maintainer  :  conal@conal.net
-- Stability   :  experimental
-- 
-- Experiment with vertex specs
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-- I'm torn about using this coding trick.  HOpenGL has a 'Vertex'
-- class.  I added instances for normals and colors, and for pairs.  Then
-- surfaces over any nested pairing of such things can be rendered.
-- Moreover, one can do interpolation and differentiation generically, if
-- the components support those operations.  However, it's not really
-- safe, given the order-sensitivity of processing of these components, and
-- specifically that the real vertex must come last.  Perhaps provide a
-- type of vertex-with-adornment, and give it a 'VectorSpace' instance.  I
-- could play the tuple game on the adornments.  Even represent the
-- vertex-with-adornment as a newtype around a pair, deriving the
-- 'VectorSpace' instance.


module Graphics.FieldTrip.Vertex where

import Graphics.Rendering.OpenGL


-- Pairs as vertices, processed left-to-right.
-- The real vertex then must be given last!

instance (Vertex v, Vertex v') => Vertex (v,v')
  where
    vertex (v,v') = vertex v >> vertex v'
    vertexv = error "vertexv: undefined on pairs"


newtype NormalV n = NormalV n

instance Normal n => Vertex (NormalV n)
  where
    vertex (NormalV n) = normal n
    vertexv = error "vertexv: undefined on NormalV"


newtype ColorV n = ColorV n

instance Color n => Vertex (ColorV n)
  where
    vertex (ColorV n) = color n
    vertexv = error "vertexv: undefined on ColorV"


-- The pairing trick provides 'VectorSpace' and 'Num' operations for free,
-- including derivatives and interpolation.  I think we could get a lot of
-- genericity out of this trick.
-- 
-- However, it's not really safe, given the order-senstivity, and
-- specifically that the real vertex must come last.