X-Git-Url: https://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=src%2FCube.hs;h=1e83a3e690d4a6b0f39cdc0b0025526650aa81db;hb=2da1ed2fd5929baa129812632068540a3c38a253;hp=8d978f732ffeb8fe2acd7f04b46a5912ede43168;hpb=1d2e0c4c6e5d766bd3ac6834d9dec298679f7c31;p=spline3.git

diff --git a/src/Cube.hs b/src/Cube.hs
index 8d978f7..1e83a3e 100644
--- a/src/Cube.hs
+++ b/src/Cube.hs
@@ -1,11 +1,14 @@
 module Cube
 where
 
+import Data.List ( (\\) )
+import Test.QuickCheck (Arbitrary(..), Gen, Positive(..), choose)
+
 import Cardinal
-import Face (Face(Face, v0, v1, v2, v3))
+import qualified Face (Face(Face, v0, v1, v2, v3))
 import FunctionValues
 import Point
-import Tetrahedron (Tetrahedron(Tetrahedron), fv)
+import Tetrahedron hiding (c)
 import ThreeDimensional
 
 data Cube = Cube { h :: Double,
@@ -16,6 +19,19 @@ data Cube = Cube { h :: Double,
             deriving (Eq)
 
 
+instance Arbitrary Cube where
+    arbitrary = do
+      (Positive h') <- arbitrary :: Gen (Positive Double)
+      i' <- choose (coordmin, coordmax)
+      j' <- choose (coordmin, coordmax)
+      k' <- choose (coordmin, coordmax)
+      fv' <- arbitrary :: Gen FunctionValues
+      return (Cube h' i' j' k' fv')
+        where
+          coordmin = -268435456 -- -(2^29 / 2)
+          coordmax = 268435456  -- +(2^29 / 2)
+
+
 instance Show Cube where
     show c =
         "Cube_" ++ subscript ++ "\n" ++
@@ -26,12 +42,14 @@ instance Show Cube where
         " ymin: " ++ (show (ymin c)) ++ "\n" ++
         " ymax: " ++ (show (ymax c)) ++ "\n" ++
         " zmin: " ++ (show (zmin c)) ++ "\n" ++
-        " zmax: " ++ (show (zmax c)) ++ "\n"
+        " zmax: " ++ (show (zmax c)) ++ "\n" ++
+        " fv: " ++ (show (Cube.fv c)) ++ "\n"
         where
           subscript =
               (show (i c)) ++ "," ++ (show (j c)) ++ "," ++ (show (k c))
 
 
+-- | Returns an empty 'Cube'.
 empty_cube :: Cube
 empty_cube = Cube 0 0 0 0 empty_values
 
@@ -97,13 +115,15 @@ instance ThreeDimensional Cube where
              y = delta * j'
              z = delta * k'
 
-    contains_point c p
-        | (x_coord p) < (xmin c) = False
-        | (x_coord p) > (xmax c) = False
-        | (y_coord p) < (ymin c) = False
-        | (y_coord p) > (ymax c) = False
-        | (z_coord p) < (zmin c) = False
-        | (z_coord p) > (zmax c) = False
+    -- | It's easy to tell if a point is within a cube; just make sure
+    --   that it falls on the proper side of each of the cube's faces.
+    contains_point c (x, y, z)
+        | x < (xmin c) = False
+        | x > (xmax c) = False
+        | y < (ymin c) = False
+        | y > (ymax c) = False
+        | z < (zmin c) = False
+        | z > (zmax c) = False
         | otherwise = True
 
 
@@ -111,43 +131,43 @@ instance ThreeDimensional Cube where
 -- Face stuff.
 
 -- | The top (in the direction of z) face of the cube.
-top_face :: Cube -> Face
-top_face c = Face v0' v1' v2' v3'
+top_face :: Cube -> Face.Face
+top_face c = Face.Face v0' v1' v2' v3'
     where
       delta = (1/2)*(h c)
-      v0' = (center c) + (delta, delta, delta)
-      v1' = (center c) + (delta, -delta, delta)
-      v2' = (center c) + (-delta, -delta, delta)
-      v3' = (center c) + (-delta, delta, delta)
+      v0' = (center c) + (delta, -delta, delta)
+      v1' = (center c) + (delta, delta, delta)
+      v2' = (center c) + (-delta, delta, delta)
+      v3' = (center c) + (-delta, -delta, delta)
 
 
 
 -- | The back (in the direction of x) face of the cube.
-back_face :: Cube -> Face
-back_face c = Face v0' v1' v2' v3'
+back_face :: Cube -> Face.Face
+back_face c = Face.Face v0' v1' v2' v3'
     where
       delta = (1/2)*(h c)
-      v0' = (center c) + (delta, delta, delta)
+      v0' = (center c) + (delta, -delta, -delta)
       v1' = (center c) + (delta, delta, -delta)
-      v2' = (center c) + (delta, -delta, -delta)
+      v2' = (center c) + (delta, delta, delta)
       v3' = (center c) + (delta, -delta, delta)
 
 
 -- The bottom face (in the direction of -z) of the cube.
-down_face :: Cube -> Face
-down_face c = Face v0' v1' v2' v3'
+down_face :: Cube -> Face.Face
+down_face c = Face.Face v0' v1' v2' v3'
     where
       delta = (1/2)*(h c)
-      v0' = (center c) + (delta, delta, -delta)
+      v0' = (center c) + (-delta, -delta, -delta)
       v1' = (center c) + (-delta, delta, -delta)
-      v2' = (center c) + (-delta, -delta, -delta)
+      v2' = (center c) + (delta, delta, -delta)
       v3' = (center c) + (delta, -delta, -delta)
 
 
 
 -- | The front (in the direction of -x) face of the cube.
-front_face :: Cube -> Face
-front_face c = Face v0' v1' v2' v3'
+front_face :: Cube -> Face.Face
+front_face c = Face.Face v0' v1' v2' v3'
     where
       delta = (1/2)*(h c)
       v0' = (center c) + (-delta, -delta, delta)
@@ -155,111 +175,324 @@ front_face c = Face v0' v1' v2' v3'
       v2' = (center c) + (-delta, delta, -delta)
       v3' = (center c) + (-delta, -delta, -delta)
 
-
 -- | The left (in the direction of -y) face of the cube.
-left_face :: Cube -> Face
-left_face c = Face v0' v1' v2' v3'
+left_face :: Cube -> Face.Face
+left_face c = Face.Face v0' v1' v2' v3'
     where
       delta = (1/2)*(h c)
-      v0' = (center c) + (-delta, -delta, delta)
-      v1' = (center c) + (delta, -delta, delta)
-      v2' = (center c) + (delta, -delta, -delta)
-      v3' = (center c) + (-delta, -delta, -delta)
+      v0' = (center c) + (delta, -delta, delta)
+      v1' = (center c) + (-delta, -delta, delta)
+      v2' = (center c) + (-delta, -delta, -delta)
+      v3' = (center c) + (delta, -delta, -delta)
 
 
 -- | The right (in the direction of y) face of the cube.
-right_face :: Cube -> Face
-right_face c = Face v0' v1' v2' v3'
+right_face :: Cube -> Face.Face
+right_face c = Face.Face v0' v1' v2' v3'
     where
       delta = (1/2)*(h c)
-      v0' = (center c) + (-delta, delta, -delta)
-      v1' = (center c) + (delta, delta, -delta)
-      v2' = (center c) + (delta, delta, delta)
-      v3' = (center c) + (-delta, delta, delta)
-
+      v0' = (center c) + (-delta, delta, delta)
+      v1' = (center c) + (delta, delta, delta)
+      v2' = (center c) + (delta, delta, -delta)
+      v3' = (center c) + (-delta, delta, -delta)
 
 
 tetrahedron0 :: Cube -> Tetrahedron
 tetrahedron0 c =
-    Tetrahedron (Cube.fv c) v0' v1' v2' v3'
+    Tetrahedron (Cube.fv c) v0' v1' v2' v3' vol
     where
       v0' = center c
       v1' = center (front_face c)
-      v2' = v0 (front_face c)
-      v3' = v1 (front_face c)
+      v2' = Face.v0 (front_face c)
+      v3' = Face.v1 (front_face c)
+      vol = 0
 
 tetrahedron1 :: Cube -> Tetrahedron
 tetrahedron1 c =
-    Tetrahedron fv' v0' v1' v2' v3'
+    Tetrahedron fv' v0' v1' v2' v3' vol
     where
       v0' = center c
       v1' = center (front_face c)
-      v2' = v1 (front_face c)
-      v3' = v2 (front_face c)
-      fv' = rotate (Cube.fv c) ccwx
+      v2' = Face.v1 (front_face c)
+      v3' = Face.v2 (front_face c)
+      fv' = rotate ccwx (Cube.fv c)
+      vol = 0
 
 tetrahedron2 :: Cube -> Tetrahedron
 tetrahedron2 c =
-    Tetrahedron fv' v0' v1' v2' v3'
+    Tetrahedron fv' v0' v1' v2' v3' vol
     where
       v0' = center c
       v1' = center (front_face c)
-      v2' = v2 (front_face c)
-      v3' = v3 (front_face c)
-      fv' = rotate (Cube.fv c) (ccwx . ccwx)
+      v2' = Face.v2 (front_face c)
+      v3' = Face.v3 (front_face c)
+      fv' = rotate ccwx $ rotate ccwx $ Cube.fv c
+      vol = 0
 
 tetrahedron3 :: Cube -> Tetrahedron
 tetrahedron3 c =
-    Tetrahedron fv' v0' v1' v2' v3'
+    Tetrahedron fv' v0' v1' v2' v3' vol
     where
       v0' = center c
       v1' = center (front_face c)
-      v2' = v3 (front_face c)
-      v3' = v1 (front_face c)
-      fv' = rotate (Cube.fv c) cwx
+      v2' = Face.v3 (front_face c)
+      v3' = Face.v0 (front_face c)
+      fv' = rotate cwx (Cube.fv c)
+      vol = 0
 
 tetrahedron4 :: Cube -> Tetrahedron
 tetrahedron4 c =
-    Tetrahedron fv' v0' v1' v2' v3'
+    Tetrahedron fv' v0' v1' v2' v3' vol
     where
       v0' = center c
       v1' = center (top_face c)
-      v2' = v0 (front_face c)
-      v3' = v1 (front_face c)
-      fv' = rotate (Cube.fv c) cwy
+      v2' = Face.v0 (top_face c)
+      v3' = Face.v1 (top_face c)
+      fv' = rotate cwy (Cube.fv c)
+      vol = 0
 
 tetrahedron5 :: Cube -> Tetrahedron
 tetrahedron5 c =
-    Tetrahedron fv' v0' v1' v2' v3'
+    Tetrahedron fv' v0' v1' v2' v3' vol
     where
       v0' = center c
       v1' = center (top_face c)
-      v2' = v1 (top_face c)
-      v3' = v2 (top_face c)
-      fv' = rotate (Tetrahedron.fv (tetrahedron0 c)) ccwx
+      v2' = Face.v1 (top_face c)
+      v3' = Face.v2 (top_face c)
+      fv' = rotate cwy $ rotate cwz $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
 
 tetrahedron6 :: Cube -> Tetrahedron
 tetrahedron6 c =
-    Tetrahedron fv' v0' v1' v2' v3'
+    Tetrahedron fv' v0' v1' v2' v3' vol
     where
       v0' = center c
       v1' = center (top_face c)
-      v2' = v2 (top_face c)
-      v3' = v3 (top_face c)
-      fv' = rotate (Tetrahedron.fv (tetrahedron0 c)) (ccwx . ccwx)
+      v2' = Face.v2 (top_face c)
+      v3' = Face.v3 (top_face c)
+      fv' = rotate cwy $ rotate cwz
+                       $ rotate cwz
+                       $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
 
 tetrahedron7 :: Cube -> Tetrahedron
 tetrahedron7 c =
-    Tetrahedron fv' v0' v1' v2' v3'
+    Tetrahedron fv' v0' v1' v2' v3' vol
     where
       v0' = center c
       v1' = center (top_face c)
-      v2' = v3 (top_face c)
-      v3' = v1 (top_face c)
-      fv' = rotate (Tetrahedron.fv (tetrahedron0 c)) cwx
+      v2' = Face.v3 (top_face c)
+      v3' = Face.v0 (top_face c)
+      fv' = rotate cwy $ rotate ccwz $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+tetrahedron8 :: Cube -> Tetrahedron
+tetrahedron8 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (back_face c)
+      v2' = Face.v0 (back_face c)
+      v3' = Face.v1 (back_face c)
+      fv' = rotate cwy $ rotate cwy $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+tetrahedron9 :: Cube -> Tetrahedron
+tetrahedron9 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (back_face c)
+      v2' = Face.v1 (back_face c)
+      v3' = Face.v2 (back_face c)
+      fv' = rotate cwy $ rotate cwy
+                       $ rotate cwx
+                       $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+tetrahedron10 :: Cube -> Tetrahedron
+tetrahedron10 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (back_face c)
+      v2' = Face.v2 (back_face c)
+      v3' = Face.v3 (back_face c)
+      fv' = rotate cwy $ rotate cwy
+                       $ rotate cwx
+                       $ rotate cwx
+                       $ Tetrahedron.fv (tetrahedron0 c)
+
+      vol = 0
+
+tetrahedron11 :: Cube -> Tetrahedron
+tetrahedron11 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (back_face c)
+      v2' = Face.v3 (back_face c)
+      v3' = Face.v0 (back_face c)
+      fv' = rotate cwy $ rotate cwy
+                       $ rotate ccwx
+                       $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+
+tetrahedron12 :: Cube -> Tetrahedron
+tetrahedron12 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (down_face c)
+      v2' = Face.v0 (down_face c)
+      v3' = Face.v1 (down_face c)
+      fv' = rotate ccwy (Tetrahedron.fv (tetrahedron0 c))
+      vol = 0
+
+
+tetrahedron13 :: Cube -> Tetrahedron
+tetrahedron13 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (down_face c)
+      v2' = Face.v1 (down_face c)
+      v3' = Face.v2 (down_face c)
+      fv' = rotate ccwy $ rotate ccwz $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+
+tetrahedron14 :: Cube -> Tetrahedron
+tetrahedron14 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (down_face c)
+      v2' = Face.v2 (down_face c)
+      v3' = Face.v3 (down_face c)
+      fv' = rotate ccwy $ rotate ccwz
+                        $ rotate ccwz
+                        $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+
+tetrahedron15 :: Cube -> Tetrahedron
+tetrahedron15 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (down_face c)
+      v2' = Face.v3 (down_face c)
+      v3' = Face.v0 (down_face c)
+      fv' = rotate ccwy $ rotate cwz $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+
+tetrahedron16 :: Cube -> Tetrahedron
+tetrahedron16 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (right_face c)
+      v2' = Face.v0 (right_face c)
+      v3' = Face.v1 (right_face c)
+      fv' = rotate ccwz (Tetrahedron.fv (tetrahedron0 c))
+      vol = 0
+
+
+tetrahedron17 :: Cube -> Tetrahedron
+tetrahedron17 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (right_face c)
+      v2' = Face.v1 (right_face c)
+      v3' = Face.v2 (right_face c)
+      fv' = rotate ccwz $ rotate cwy $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+
+tetrahedron18 :: Cube -> Tetrahedron
+tetrahedron18 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (right_face c)
+      v2' = Face.v2 (right_face c)
+      v3' = Face.v3 (right_face c)
+      fv' = rotate ccwz $ rotate cwy
+                        $ rotate cwy
+                        $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+
+tetrahedron19 :: Cube -> Tetrahedron
+tetrahedron19 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (right_face c)
+      v2' = Face.v3 (right_face c)
+      v3' = Face.v0 (right_face c)
+      fv' = rotate ccwz $ rotate ccwy
+                        $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+
+tetrahedron20 :: Cube -> Tetrahedron
+tetrahedron20 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (left_face c)
+      v2' = Face.v0 (left_face c)
+      v3' = Face.v1 (left_face c)
+      fv' = rotate cwz (Tetrahedron.fv (tetrahedron0 c))
+      vol = 0
+
+
+tetrahedron21 :: Cube -> Tetrahedron
+tetrahedron21 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (left_face c)
+      v2' = Face.v1 (left_face c)
+      v3' = Face.v2 (left_face c)
+      fv' = rotate cwz $ rotate ccwy $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+
+tetrahedron22 :: Cube -> Tetrahedron
+tetrahedron22 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (left_face c)
+      v2' = Face.v2 (left_face c)
+      v3' = Face.v3 (left_face c)
+      fv' = rotate cwz $ rotate ccwy
+                       $ rotate ccwy
+                       $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
+
+tetrahedron23 :: Cube -> Tetrahedron
+tetrahedron23 c =
+    Tetrahedron fv' v0' v1' v2' v3' vol
+    where
+      v0' = center c
+      v1' = center (left_face c)
+      v2' = Face.v3 (left_face c)
+      v3' = Face.v0 (left_face c)
+      fv' = rotate cwz $ rotate cwy
+                       $ Tetrahedron.fv (tetrahedron0 c)
+      vol = 0
+
 
-tetrahedrons :: Cube -> [Tetrahedron]
-tetrahedrons c =
+tetrahedra :: Cube -> [Tetrahedron]
+tetrahedra c =
     [tetrahedron0 c,
      tetrahedron1 c,
      tetrahedron2 c,
@@ -267,24 +500,163 @@ tetrahedrons c =
      tetrahedron4 c,
      tetrahedron5 c,
      tetrahedron6 c,
-     tetrahedron7 c
-                -- ,
-                --  tetrahedron8 c,
-                --  tetrahedron9 c,
-                --  tetrahedron10 c,
-                --  tetrahedron11 c,
-                --  tetrahedron12 c,
-                --  tetrahedron13 c,
-                --  tetrahedron14 c,
-                --  tetrahedron15 c,
-                --  tetrahedron16 c,
-                --  tetrahedron17 c,
-                --  tetrahedron18 c,
-                --  tetrahedron19 c,
-                --  tetrahedron20 c,
-                --  tetrahedron21 c,
-                --  tetrahedron21 c,
-                --  tetrahedron22 c,
-                --  tetrahedron23 c,
-                --  tetrahedron24 c
-    ]
+     tetrahedron7 c,
+     tetrahedron8 c,
+     tetrahedron9 c,
+     tetrahedron10 c,
+     tetrahedron11 c,
+     tetrahedron12 c,
+     tetrahedron13 c,
+     tetrahedron14 c,
+     tetrahedron15 c,
+     tetrahedron16 c,
+     tetrahedron17 c,
+     tetrahedron18 c,
+     tetrahedron19 c,
+     tetrahedron20 c,
+     tetrahedron21 c,
+     tetrahedron22 c,
+     tetrahedron23 c]
+
+-- | All completely contained in the front half of the cube.
+front_half_tetrahedra :: Cube -> [Tetrahedron]
+front_half_tetrahedra c =
+  [tetrahedron0 c,
+   tetrahedron1 c,
+   tetrahedron2 c,
+   tetrahedron3 c,
+   tetrahedron6 c,
+   tetrahedron12 c,
+   tetrahedron19 c,
+   tetrahedron21 c]
+
+
+-- | All tetrahedra completely contained in the top half of the cube.
+top_half_tetrahedra :: Cube -> [Tetrahedron]
+top_half_tetrahedra c =
+  [tetrahedron4 c,
+   tetrahedron5 c,
+   tetrahedron6 c,
+   tetrahedron7 c,
+   tetrahedron0 c,
+   tetrahedron10 c,
+   tetrahedron16 c,
+   tetrahedron20 c]
+
+
+-- | All tetrahedra completely contained in the back half of the cube.
+back_half_tetrahedra :: Cube -> [Tetrahedron]
+back_half_tetrahedra c =
+  [tetrahedron8 c,
+   tetrahedron9 c,
+   tetrahedron10 c,
+   tetrahedron11 c,
+   tetrahedron4 c,
+   tetrahedron14 c,
+   tetrahedron17 c,
+   tetrahedron23 c]
+
+
+-- | All tetrahedra completely contained in the down half of the cube.
+down_half_tetrahedra :: Cube -> [Tetrahedron]
+down_half_tetrahedra c =
+  [tetrahedron12 c,
+   tetrahedron13 c,
+   tetrahedron14 c,
+   tetrahedron15 c,
+   tetrahedron2 c,
+   tetrahedron8 c,
+   tetrahedron18 c,
+   tetrahedron22 c]
+
+
+-- | All tetrahedra completely contained in the right half of the cube.
+right_half_tetrahedra :: Cube -> [Tetrahedron]
+right_half_tetrahedra c =
+  [tetrahedron16 c,
+   tetrahedron17 c,
+   tetrahedron18 c,
+   tetrahedron19 c,
+   tetrahedron1 c,
+   tetrahedron5 c,
+   tetrahedron9 c,
+   tetrahedron13 c]
+
+
+-- | All tetrahedra completely contained in the left half of the cube.
+left_half_tetrahedra :: Cube -> [Tetrahedron]
+left_half_tetrahedra c =
+  [tetrahedron20 c,
+   tetrahedron21 c,
+   tetrahedron22 c,
+   tetrahedron23 c,
+   tetrahedron3 c,
+   tetrahedron7 c,
+   tetrahedron11 c,
+   tetrahedron15 c]
+
+
+in_top_half :: Cube -> Point -> Bool
+in_top_half c (_,_,z) =
+  distance_from_top <= distance_from_bottom
+  where
+    distance_from_top = abs $ (zmax c) - z
+    distance_from_bottom = abs $ (zmin c) - z
+
+in_front_half :: Cube -> Point -> Bool
+in_front_half c (x,_,_) =
+    distance_from_front <= distance_from_back
+  where
+    distance_from_front = abs $ (xmin c) - x
+    distance_from_back = abs $ (xmax c) - x
+
+
+in_left_half :: Cube -> Point -> Bool
+in_left_half c (_,y,_) =
+    distance_from_left <= distance_from_right
+  where
+    distance_from_left = abs $ (ymin c) - y
+    distance_from_right = abs $ (ymax c) - y
+
+
+-- | Takes a 'Cube', and returns the Tetrahedra belonging to it that
+--   contain the given 'Point'. This should be faster than checking
+--   every tetrahedron individually, since we determine which half
+--   (hemisphere?) of the cube the point lies in three times: once in
+--   each dimension. This allows us to eliminate non-candidates
+--   quickly.
+--
+--   This can throw an exception, but the use of 'head' might
+--   save us some unnecessary computations.
+--
+find_containing_tetrahedron :: Cube -> Point -> Tetrahedron
+find_containing_tetrahedron c p =
+  head containing_tetrahedra
+  where
+    candidates = tetrahedra c
+    non_candidates_x =
+        if (in_front_half c p) then
+          back_half_tetrahedra c
+        else
+          front_half_tetrahedra c
+
+    candidates_x = candidates \\ non_candidates_x
+
+    non_candidates_y =
+      if (in_left_half c p) then
+        right_half_tetrahedra c
+      else
+        left_half_tetrahedra c
+
+    candidates_xy = candidates_x \\ non_candidates_y
+
+    non_candidates_z =
+      if (in_top_half c p) then
+        down_half_tetrahedra c
+      else
+        top_half_tetrahedra c
+
+    candidates_xyz = candidates_xy \\ non_candidates_z
+
+    contains_our_point = flip contains_point p
+    containing_tetrahedra = filter contains_our_point candidates_xyz