Implement (not fully working) alternate shadow volumes

src/Shader/Poke.hs

@@ -4,6 +4,7 @@ module Shader.Poke
     , pokeArrayOff
     , pokeShape
     , pokeWallsWindowsFloor
+    , memoTopPrismEdgeIndices
     ) where
 import Shader.Data
 import Shader.Parameters