coordmap (cam::Mat 4 4 Float) (p::Vec 4 Float)
    = cam *. p

blendplane = -- NoBlending -- BlendLogicOp Xor
    Blend (FuncAdd,FuncAdd)
          ((OneBF,SrcAlpha),(DstAlpha,DstAlpha))
          (V4 0 0 0 0)

point :: Vec 3 Float -> Vec 4 Float
point p = V4 p%x p%y p%z 1


makeFrame (cubemap :: Texture)
          (skybox :: PrimitiveStream Triangle ((Vec 3 Float)))
          (cameraPosition :: Vec 3 Float)
          (cam ::  Mat 4 4 Float)
          (color :: Vec 4 Float)
          (texture :: Texture)
          (prims :: PrimitiveStream Triangle (Vec 4 Float, Vec 3 Float, Vec 3 Float))
          (plane :: PrimitiveStream Triangle ((Vec 4 Float)))

    = imageFrame (emptyDepthImage 1, emptyColorImage (V4 0 0 0.4 1))
  `overlay`
      skybox
    & mapPrimitives (\((p)) -> let texcoord = V3 p%x (p%y) (p%z)
                                   p' = cam *. point (p + cameraPosition)
                                in (p', texcoord))
    & rasterizePrimitives (TriangleCtx CullNone PolygonFill NoOffset LastVertex) ((Smooth))
    & mapFragments (\((d)) -> ((texture2D (Sampler PointFilter MirroredRepeat cubemap) d%xy )))
    & accumulateWith (DepthOp Always False, ColorOp NoBlending (V4 True True True True))
  `overlay`
      prims
    & mapPrimitives (\(p,n,uvw) -> ( coordmap cam p, V2 uvw%x (1 - uvw%y) ))
    & rasterizePrimitives (TriangleCtx CullBack PolygonFill NoOffset LastVertex) ((Smooth))
    & mapFragments (\((uv)) -> ((color * texture2D (Sampler PointFilter MirroredRepeat texture) uv )))
    & accumulateWith (DepthOp Less True, ColorOp NoBlending (V4 True True True True))
  `overlay`
      plane
    & mapPrimitives (\((p)) -> let p' = coordmap cam p in (p', p%xz))
    & rasterizePrimitives (TriangleCtx CullNone PolygonFill NoOffset LastVertex) ((Smooth))
    & mapFragments (\((uv)) -> let c = mixB zero one (fract uv >= (one *! (0.95::Float)))
                                   r = V4 1 1 1 0 *! (max c%x c%y)
                                in ((r + V4 0 0 0 (0.8))))
    & accumulateWith (DepthOp Less True, ColorOp blendplane (V4 True True True True))

textureCubeSlot s = Texture2DSlot s

main = renderFrame $
   makeFrame (textureCubeSlot "CubeMap")
             (fetch "SkyCube" ((Attribute "position")))
             (Uniform "CameraPosition")
             (Uniform "ViewProjection")
             (Uniform "diffuseColor")
             (Texture2DSlot "diffuseTexture")
             (fetch "objects" (Attribute "position", Attribute "normal", Attribute "uvw"))
             (fetch "plane"   ((Attribute "position")))