1 files changed, 13 insertions, 8 deletions

diff --git a/Spear/Math/Plane.hs b/Spear/Math/Plane.hs
index b20740c..08e4570 100644
--- a/Spear/Math/Plane.hs
+++ b/Spear/Math/Plane.hs
@@ -6,12 +6,9 @@ module Spear.Math.Plane
 )
 where
 
-
 import Spear.Math.Vector
 
-
-data PointPlanePos = Front | Back | Contained deriving (Eq, Ord, Show)
-
+data PointPlanePos = Front | Back | Contained deriving (Eq, Show)
 
 data Plane = Plane
     { n :: {-# UNPACK #-} !Vector3,
@@ -19,13 +16,21 @@ data Plane = Plane
     }
     deriving(Eq, Show)
 
-
--- | Create a plane given a normal vector and a distance from the origin.
+-- | Construct a plane from  a normal vector and a distance from the origin.
 plane :: Vector3 -> Float -> Plane
 plane n d = Plane (normalise n) d
 
-
--- | Classify the given point's relative position with respect to the given plane.
+-- | Construct a plane from three points.
+--
+-- Points must be given in counter-clockwise order.
+fromPoints :: Vector3 -> Vector3 -> Vector3 -> Plane
+fromPoints p0 p1 p2 = Plane n d
+           where n  = normalise $ v1 `cross` v2
+                 v1 = p2 - p1
+                 v2 = p0 - p1
+                 d  = p0 `dot` n
+
+-- | Classify the given point's relative position with respect to the plane.
 classify :: Plane -> Vector3 -> PointPlanePos
 classify (Plane n d) pt =
     case (n `dot` pt - d) `compare` 0 of