Position.hs

{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE ViewPatterns  #-}

--
-- Generators for various distributions of particle positions
--
module Random.Position
  where

import Common.Type

import System.Random.MWC                                ( uniformR )
import Data.Array.Accelerate.Examples.Internal          ( (:~>) )
import Data.Array.Accelerate.Array.Sugar                as A


-- | Points distributed as a disc
--
disc :: Position -> R -> sh :~> Position
disc (V3 originX originY originZ) radiusMax _ix gen
  = do  radius          <- uniformR (0,radiusMax) gen
        theta           <- uniformR (0, pi)       gen
        phi             <- uniformR (0, 2*pi)     gen

        return $ V3 (originX + radius * sin theta * cos phi)
                    (originY + radius * sin theta * sin phi)
                    (originZ + radius * cos theta)


-- | A point cloud with areas of high and low density
--
cloud :: Shape sh => (Int,Int) -> R -> sh :~> Position
cloud (fromIntegral -> sizeX, fromIntegral -> sizeY) radiusMax ix gen
  = let
        blob (sx,sy,sz) r
          = disc (V3 (sx * sizeX) (sy * sizeY) (sz * (sizeX `min` sizeY)))
                 (radiusMax * r)

    in case A.size ix `mod` 5 of
        0 -> blob ( 0.25, 0.25, 0.25) 1.00 ix gen
        1 -> blob (-0.10, 0.10, 0.10) 0.60 ix gen
        2 -> blob (-0.05, 0.30,-0.30) 0.35 ix gen
        3 -> blob (-0.20,-0.12,-0.12) 0.45 ix gen
        _ -> blob ( 0.15,-0.10, 0.20) 0.75 ix gen