added height function

src/Map/Map.hs

@@ -1,9 +1,11 @@
 module Map.Map where
 
 import Map.Types
+import Map.Creation
 
-import Data.Array (bounds)
-import Data.List  (sort, group)
+import Data.Function (on)
+import Data.Array    (bounds, (!))
+import Data.List     (sort, sortBy, group)
 
 -- WARNING: Does NOT Check for neighbours exceeding maximum map coordinates yet.
 unsafeGiveNeighbours :: (Int, Int)  -- ^ original coordinates
@@ -36,6 +38,60 @@ giveNeighbourhood _  0 (a,b) = [(a,b)]
 giveNeighbourhood mp n (a,b) = let ns = giveNeighbours mp (a,b) in 
                              remdups . concat $ ns : map (giveNeighbourhood mp (n-1)) ns
 
+-- | Calculates the height of any given point on the map.
+-- Does not add camera distance to ground to that.
+-- 
+-- This ueses barycentric coordinate stuff. Wanna read more?
+-- http://en.wikipedia.org/wiki/Barycentric_coordinate_system_%28mathematics%29
+-- http://www.alecjacobson.com/weblog/?p=1596
+--
+giveMapHeight :: PlayMap
+              -> (Float, Float)  -- ^ Coordinates on X/Z-axes 
+              -> Float           -- ^ Terrain Height at that position
+giveMapHeight mp (x,z) = let [a,b,c] = getTrianglePoints [tff,tfc,tcf,tcc]
+                             ar = area (fi a) (fi b) (fi c)
+                             λa = area (fi b) (fi c) (x, z) / ar
+                             λb = area (fi a) (fi c) (x, z) / ar
+                             λc = area (fi a) (fi b) (x, z) / ar
+                         in  (λa * hlu a) + (λb * hlu b) + (λc * hlu c)
+  where
+
+    fi :: (Int, Int) -> (Float, Float)
+    fi (m, n) = (fromIntegral m, fromIntegral n)
+
+    -- Height LookUp
+    hlu :: (Int, Int) -> Float
+    hlu (k,j) = let node = mp ! (k,j)
+                in  case node of
+                    (Full    _ y _ _ _ _ _ _) -> y
+                    (Minimal _              ) -> 1.0
+
+    ff  = (floor   x, floor   z) :: (Int, Int)
+    fc  = (floor   x, ceiling z) :: (Int, Int)
+    cf  = (ceiling x, floor   z) :: (Int, Int)
+    cc  = (ceiling x, ceiling z) :: (Int, Int)
+
+    tff = (ff, dist (x,z) ff)
+    tfc = (fc, dist (x,z) fc)
+    tcf = (cf, dist (x,z) cf)
+    tcc = (cc, dist (x,z) cc)
+
+    getTrianglePoints :: [((Int,Int), Float)] -> [(Int,Int)]
+    getTrianglePoints = ((take 3) . (map fst) . (sortBy (compare `on` snd)))
+
+    dist :: (Float, Float) -> (Int, Int) -> Float
+    dist (x1,z1) (x2,z2) = let x' = x1 - fromIntegral x2
+                               z' = z1 - fromIntegral z2
+                           in  sqrt $ x'*x' + z'*z'
+
+    -- Heron's Formula: http://en.wikipedia.org/wiki/Heron%27s_formula
+    area :: (Float, Float) -> (Float, Float) -> (Float, Float) -> Float
+    area (x1,z1) (x2,z2) (x3,z3) = let a = sqrt $ (x1-x2)*(x1-x2) + (z1-z2)*(z1-z2)
+                                       b = sqrt $ (x2-x3)*(x2-x3) + (z2-z3)*(z2-z3)
+                                       c = sqrt $ (x1-x3)*(x1-x3) + (z1-z3)*(z1-z3)
+                                       s = (a+b+c)/2 
+                                   in  sqrt $ s * (s-a) * (s-b) * (s-c)
+
 -- removing duplicates in O(n log n), losing order and adding Ord requirement
 remdups :: Ord a => [a] -> [a]
 remdups = map head . group . sort