dark = V4 0.1 0.0 0.2 1
clear = FrameBuffer $ (DepthImage @1 1000, ColorImage @1 dark)   -- ...

triangleRasterCtx = TriangleCtx CullNone PolygonFill NoOffset LastVertex
colorFragmentCtx = (DepthOp Less True, ColorOp NoBlending (V4 True True True True))

rasterizeWith = rasterizePrimitives
triangles = triangleRasterCtx

cubeVertexStream = fetch "stream4" ((Attribute "position4" :: Vec 4 Float))
mapFragments2 s fs = accumulate colorFragmentCtx (\((a)) -> ((fs a))) s clear
transform s f = mapPrimitives (\((v)) -> (f v, v)) s

rotate' v = (Uniform "MVP" :: Mat 4 4 Float) `PrimMulMatVec` v

main =             cubeVertexStream         -- cube vertices
    `transform`    (scale 0.5 . rotate')    -- scale them
     &             rasterizeWith triangles ((Smooth))  -- rasterize
    `mapFragments2` (\a -> if a%r < 0.5 then blue else red)
     &             ScreenOut                -- draw into screen