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" Triangle (Attribute "position4" :: Vec 4 Float)
mapFragments2 s fs = accumulate colorFragmentCtx (\a -> fs a) s clear

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

main =             cubeVertexStream         -- cube vertices
     &             mapPrimitives (\v -> (scale 0.5 . rotate' $ v, v))
     &             rasterizeWith triangles Smooth  -- rasterize
    `mapFragments2` id                       -- set every pixel blue
     &             ScreenOut                -- draw into screen