clear = FrameBuffer $ ColorImage @1 $ V4 1 0 0 0.5

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

rasterizeWith = rasterizePrimitives
triangles = triangleRasterCtx

quadVertexStream = fetch "quad" Triangle (Attribute "position" :: Vec 4 Float)

transform s f =  mapPrimitives (\v -> f v) s

mapFragments2 s fs = accumulate colorFragmentCtx  ( \a -> fs a) s clear

render f = quadVertexStream                 -- id vertices
    `transform`    id
     &             rasterizeWith triangles ()  -- rasterize
    `mapFragments2` f
     &             ScreenOut                --  draw into screen

main = render $ const blue