From bb51e8025f178d7423c5404b8e8e6909f856907b Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Tue, 24 Dec 2024 12:06:32 -0800
Subject: Add axis-aligned plane.

---
 Spear/Math/Plane.hs | 60 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 47 insertions(+), 13 deletions(-)

diff --git a/Spear/Math/Plane.hs b/Spear/Math/Plane.hs
index 5440a43..cbf5aed 100644
--- a/Spear/Math/Plane.hs
+++ b/Spear/Math/Plane.hs
@@ -2,41 +2,75 @@
 
 module Spear.Math.Plane
 (
-    Plane
-,   plane
-,   classify
+  Plane(..)
+, AxisPlane(..)
+, plane
+, axisPlane
+, planeClassify
+, axisPlaneClassify
 )
 where
 
 import           Spear.Math.Vector
 import           Spear.Prelude
 
+
+data Axis = X | Y | Z deriving (Eq, Show)
+
+data AxisOrientation = PositiveAxis | NegativeAxis deriving (Eq, Show)
+
 data PointPlanePos = Front | Back | Contained deriving (Eq, Show)
 
+-- | A 3D plane.
 data Plane = Plane
-    { n :: {-# UNPACK #-} !Vector3,
-      d :: {-# UNPACK #-} !Float
+    { planeNormal   :: {-# UNPACK #-} !Vector3
+    , planeDistance :: {-# UNPACK #-} !Float
     }
     deriving(Eq, Show)
 
+-- | An axis-aligned 3D plane.
+data AxisPlane = AxisPlane
+    { axisPlaneAxis     :: !Axis
+    , axisPlaneDistance :: {-# UNPACK #-} !Float
+    , axisPlaneNormal   :: !AxisOrientation
+    }
+    deriving (Eq, Show)
+
+
 -- | Construct a plane from  a normal vector and a distance from the origin.
 plane :: Vector3 -> Float -> Plane
 plane n d = Plane (normalise n) d
 
+-- | Construct an axis-aligned plane.
+axisPlane :: Axis -> Float -> AxisOrientation -> AxisPlane
+axisPlane = AxisPlane
+
 -- | 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
+planeFromPoints :: Vector3 -> Vector3 -> Vector3 -> Plane
+planeFromPoints 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 =
+planeClassify :: Plane -> Vector3 -> PointPlanePos
+planeClassify (Plane n d) pt =
     case (n `dot` pt - d) `compare` 0 of
         GT -> Front
         LT -> Back
         EQ -> Contained
+
+-- | Classify the given point's relative position with respect to the plane.
+axisPlaneClassify :: AxisPlane -> Vector3 -> PointPlanePos
+axisPlaneClassify (AxisPlane axis d _) (Vector3 x y z) =
+    let classify coord
+          | coord < d = Back
+          | coord > d = Front
+          | otherwise = Contained
+    in case axis of
+        X -> classify x
+        Y -> classify y
+        Z -> classify z
-- 
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