clear = FrameBuffer $ (DepthImage @1 1000, ColorImage @1 red)   -- ...
clear' = FrameBuffer $ (DepthImage @1 1000, ColorImage @1 blue)   -- ...

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

rasterizeWith = rasterizePrimitives
triangles = triangleRasterCtx

cubeVertexStream = fetch "stream4" (Attribute "position4" :: Vec 4 Float, Attribute "vertexUV" :: Vec 2 Float)
mapFragments2 s fs = accumulate colorFragmentCtx (\((a)) -> ((fs a))) s clear
transform s f =  mapPrimitives (\(v,uv) -> (f v, uv)) s

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

sampler = Sampler LinearFilter MirroredRepeat $ Texture2D (V2 128 128) (PrjImageColor clear')

main =             cubeVertexStream         -- cube vertices
    `transform`    (scale 0.5 . rotate')    -- scale them
     &             rasterizeWith triangles ((Smooth))  -- rasterize
    `mapFragments2` (texture2D sampler)
     &             ScreenOut                --  draw into screen