clear = FrameBuffer $ ColorImage @1 red   -- ...

triangleRasterCtx = TriangleCtx CullNone PolygonFill NoOffset LastVertex
colorFragmentCtx = accumulationContext (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
transform s f =  mapPrimitives (\v -> f v) s

rotate :: Float -> Vec 4 Float -> Vec 4 Float
rotate a v = M44F (V4 c (-s) 0 0) (V4 s c 0 0) (V4 0 0 1 0) (V4 0 0 0 1) `PrimMulMatVec` v
  where
    c = PrimCos a
    s = PrimSin a

main =             cubeVertexStream      -- cube vertices
    `transform`    (scale 0.1 . rotate 3)             -- scale them
     &             rasterizeWith triangles ()  -- rasterize
    `mapFragments2` const blue                -- set every pixel blue
     &             ScreenOut                 --  draw into screen