Move towards geometry instancing for shadows

src/Shader/Poke.hs

@@ -162,13 +162,15 @@ topPrismIndices n = concatMap f [1..n-2]    -- triangles on top face
     g x = [2*x,2*x+1,2*x+3
             ,2*x,2*x+3,2*x+2]
 
+-- consider changing the position to a vec4
+-- and just doing two pokes rather than seven
+-- (especially if adding normal data)
 pokeJustV :: Ptr Float
     -> Int
     -> ShapeV 
     -> IO Int
 {-# INLINE pokeJustV #-}
 pokeJustV ptr nv sh = do
---    pokeArray (advancePtr ptr (off 0)) [a,b,c,d,e,f,g]
     pokeElemOff ptr (off 0) a
     pokeElemOff ptr (off 1) b
     pokeElemOff ptr (off 2) c