From 4d622a038f7a4e34a3252843aacfa70fd072f502 Mon Sep 17 00:00:00 2001
From: Marc Sunet <jeannekamikaze@gmail.com>
Date: Mon, 6 Aug 2012 13:25:11 +0200
Subject: Initial implementation

---
 Spear/Math/Quaternion.hs | 109 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)

diff --git a/Spear/Math/Quaternion.hs b/Spear/Math/Quaternion.hs
index e69de29..4eb88d7 100644
--- a/Spear/Math/Quaternion.hs
+++ b/Spear/Math/Quaternion.hs
@@ -0,0 +1,109 @@
+module Spear.Math.Quaternion
+(
+    Quaternion
+    -- * Construction
+,   quat
+,   qvec4
+,   qvec3
+,   qAxisAngle
+    -- * Operations
+,   qmul
+,   qconj
+,   qinv
+,   Spear.Math.Quaternion.normalise
+,   Spear.Math.Quaternion.norm
+,   qrot
+)
+where
+
+
+import qualified Spear.Math.Vector3 as V3
+import Spear.Math.Vector4 as V4
+
+
+newtype Quaternion = Quaternion { getVec :: Vector4 }
+
+
+-- | Build a 'Quaternion'.
+quat :: Float -- x
+     -> Float -- y
+     -> Float -- z
+     -> Float -- w
+     -> Quaternion
+quat x y z w = Quaternion $ vec4 x y z w
+
+
+-- | Build a 'Quaternion' from the given 'Vector4'.
+qvec4 :: Vector4 -> Quaternion
+qvec4 = Quaternion
+
+
+-- | Build a 'Quaternion' from the given 'Vector3' and w.
+qvec3 :: V3.Vector3 -> Float -> Quaternion
+qvec3 v w = Quaternion $ vec4 (V3.x v) (V3.y v) (V3.z v) w
+
+
+-- | Build a 'Quaternion' representing the given rotation.
+qAxisAngle :: V3.Vector3 -> Float -> Quaternion
+qAxisAngle axis angle =
+    let s' = V3.norm axis
+        s  = if s' == 0 then 1 else s'
+        a  = angle * toRAD * 0.5
+        sa = sin a
+        w  = cos a
+        x  = V3.x axis * sa * s
+        y  = V3.y axis * sa * s
+        z  = V3.z axis * sa * s
+    in
+        Quaternion $ vec4 x y z w
+
+
+-- | Compute the product of the given two quaternions.
+qmul :: Quaternion -> Quaternion -> Quaternion
+qmul (Quaternion q1) (Quaternion q2) =
+    let x1 = x q1
+        y1 = y q1
+        z1 = z q1
+        w1 = w q1
+        x2 = x q2
+        y2 = y q2
+        z2 = y q2
+        w2 = w q2
+        w' = w1*w2 - x1*x2 - y1*y2 - z1*z2
+        x' = w1*x2 + x1*w2 + y1*z2 - z1*y2
+        y' = w1*y2 - x1*z2 + y1*w2 + z1*x2
+        z' = w1*z2 + x1*y2 - y1*x2 + z1*w2
+    in
+        Quaternion $ vec4 x' y' z' w'
+
+
+-- | Compute the conjugate of the given 'Quaternion'.
+qconj :: Quaternion -> Quaternion
+qconj (Quaternion q) = Quaternion $ vec4 (-x q) (-y q) (-z q) (w q)
+
+
+-- | Invert the given 'Quaternion'.
+qinv :: Quaternion -> Quaternion
+qinv (Quaternion q) =
+    let m = normSq q
+    in Quaternion $ vec4 (-x q / m) (-y q / m) (-z q / m) (w q / m)
+
+
+-- | Normalise the given 'Quaternion'.
+normalise :: Quaternion -> Quaternion
+normalise = Quaternion . V4.normalise . getVec
+
+
+-- | Compute the norm of the given 'Quaternion'.
+norm :: Quaternion -> Float
+norm = V4.norm . getVec
+
+
+-- | Rotate the given 'Vector3'.
+qrot :: Quaternion -> V3.Vector3 -> V3.Vector3
+qrot q v = toVec3 $ q `qmul` qvec3 v 0 `qmul` qconj q
+    where toVec3 (Quaternion q) = V3.vec3 (x q) (y q) (z q)
+
+
+toRAD = pi / 180
+
-- 
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