clear' = FrameBuffer $ (DepthImage @1 1000, ColorImage @1 navy)   -- ...
clear = FrameBuffer $ (DepthImage @1 1000, ColorImage @1 maroon)   -- ...

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
mapFragments22 s fs = accumulate colorFragmentCtx  ( \((a)) -> ((fs a))) s clear'
transform s f =  mapPrimitives (\(v,u) -> (f v, u)) s

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

cube fb =           cubeVertexStream         -- cube vertices
    `transform`    (scale 0.5 . rotate')    -- scale them
     &             rasterizeWith triangles ((Smooth))  -- rasterize
    `mapFragments23` (\a -> a%xyxy)
 where mapFragments23 s fs = accumulate colorFragmentCtx  ( \((a)) -> ((fs a))) s fb

cube' fb =             cubeVertexStream         -- cube vertices
    `transform`    (scale 1.0 . rotate')    -- scale them
     &             rasterizeWith triangles ((Smooth))  -- rasterize
    `mapFragments2` (\a -> texture2D sampler a * V4 0.7 0.7 0.7 1)
  where sampler = Sampler LinearFilter MirroredRepeat $ Texture2D (V2 1024 768) (PrjImageColor fb)

main = ScreenOut $ cube' $ cube' $ cube' $ cube' $ cube' $ cube clear