1 files changed, 18 insertions, 0 deletions

diff --git a/Spear/Math/MatrixUtils.hs b/Spear/Math/MatrixUtils.hs
new file mode 100644
index 0000000..88ad3b1
--- /dev/null
+++ b/Spear/Math/MatrixUtils.hs
@@ -0,0 +1,18 @@
+module Spear.Math.MatrixUtils
+(
+    fastNormalMatrix
+)
+where
+
+
+import Spear.Math.Matrix3 as M3
+import Spear.Math.Matrix4 as M4
+
+
+fastNormalMatrix :: Matrix4 -> Matrix3
+fastNormalMatrix m =
+    let m' = M4.transpose . M4.inverseTransform $ m
+    in  M3.mat3
+        (M4.m00 m') (M4.m10 m') (M4.m20 m')
+        (M4.m01 m') (M4.m11 m') (M4.m21 m')
+        (M4.m02 m') (M4.m12 m') (M4.m22 m')