len2 v = v%x*v%x + v%y*v%y + v%z*v%z

makeFrame (time :: Float)
          (vertexstream :: PrimitiveStream Triangle ((Vec 4 Float)))

    = imageFrame (emptyDepthImage 1, emptyColorImage navy)
  `overlay`
      vertexstream
    & mapPrimitives (\((x)) -> (scale 0.5 (projmat *. x), x))
    & rasterizePrimitives (TriangleCtx CullNone PolygonFill NoOffset LastVertex) ((Smooth))
    & filterFragments ffilter
    & accumulateWith (DepthOp Less True, ColorOp NoBlending (V4 True True True True))
  where
    h = 0.25

    projmat = perspective 0.1 100.0 (30 * pi / 180) 1.0
          .*. lookat (V3 3.0 1.3 0.3) (V3 0.0 0.0 0.0) (V3 0.0 1.0 0.0)
          .*. rotMatrixY (pi / 24.0 * time)

    ffilter ((v)) =
           (v%y + v%x + v%z > 1 || abs (v%y - v%x + v%z - 1.0) > h)
        && (v%y + v%x - v%z > 1 || abs (v%y + v%x + v%z - 1.0) > h)
        && (v%y - v%x - v%z > 1 || abs (v%y + v%x - v%z - 1.0) > h)
        && (v%y - v%x + v%z > 1 || abs (v%y - v%x - v%z - 1.0) > h)
        && len2 v' > abs (3 * sin (1 * time))
      where
        v' = sin (v *! 20)

main = renderFrame $
   makeFrame (Uniform "Time")
             (fetch "stream4" ((Attribute "position4")))