diff --git a/src/na.rs b/src/na.rs
index aab2cea4..b6b56643 100644
--- a/src/na.rs
+++ b/src/na.rs
@@ -83,6 +83,27 @@ pub fn one<T: One>() -> T {
 //
 //
 
+/*
+ * Perspective
+ */
+/// Computes a projection matrix given the frustrum near plane width, height, the field of
+/// view, and the distance to the clipping planes (`znear` and `zfar`).
+pub fn perspective3d<N: Real + Cast<f32> + Zero + One>(width: N, height: N, fov: N, znear: N, zfar: N) -> Mat4<N> {
+    let aspect = width / height;
+
+    let _1: N = one();
+    let sy    = _1 / (fov * cast(0.5)).tan();
+    let sx    = -sy / aspect;
+    let sz    = -(zfar + znear) / (znear - zfar);
+    let tz    = zfar * znear * cast(2.0) / (znear - zfar);
+
+    Mat4::new(
+        sx,     zero(), zero(), zero(),
+        zero(), sy,     zero(), zero(),
+        zero(), zero(), sz,     tz,
+        zero(), zero(), one(),  zero())
+}
+
 /*
  * Translation<V>
  */
diff --git a/src/structs/spec/mat.rs b/src/structs/spec/mat.rs
index 8a1d0446..ccd307c2 100644
--- a/src/structs/spec/mat.rs
+++ b/src/structs/spec/mat.rs
@@ -1,9 +1,8 @@
 use std::num::{Zero, One};
 use structs::vec::{Vec2, Vec3, Vec2MulRhs, Vec3MulRhs};
 use structs::mat::{Mat1, Mat2, Mat3, Mat3MulRhs, Mat2MulRhs};
-use structs::mat;
-use traits::operations::{Inv};
-use traits::structure::{Cast, Row, Col};
+use traits::operations::Inv;
+use traits::structure::{Row, Col};
 
 // some specializations:
 impl<N: Num + Clone>
@@ -264,25 +263,3 @@ impl<N: Mul<N, N> + Add<N, N>> Mat2MulRhs<N, Vec2<N>> for Vec2<N> {
         )
     }
 }
-
-// FIXME: move this to another file?
-impl<N: Real + Cast<f32> + Zero + One> mat::Mat4<N> {
-    /// Computes a projection matrix given the frustrum near plane width, height, the field of
-    /// view, and the distance to the clipping planes (`znear` and `zfar`).
-    pub fn new_perspective(width: N, height: N, fov: N, znear: N, zfar: N) -> mat::Mat4<N> {
-        let aspect = width / height;
-
-        let _1: N = One::one();
-        let sy    = _1 / (fov * Cast::from(0.5)).tan();
-        let sx    = -sy / aspect;
-        let sz    = -(zfar + znear) / (znear - zfar);
-        let tz    = zfar * znear * Cast::from(2.0) / (znear - zfar);
-
-        mat::Mat4::new(
-            sx,           Zero::zero(), Zero::zero(), Zero::zero(),
-            Zero::zero(), sy,           Zero::zero(), Zero::zero(),
-            Zero::zero(), Zero::zero(), sz,           tz,
-            Zero::zero(), Zero::zero(), One::one(),   Zero::zero()
-            )
-    }
-}