From c28e28f6be11f2c77e6a184ef88df4674f6ccf6b Mon Sep 17 00:00:00 2001
From: Jonathan Cornaz <jonathan.cornaz@gmail.com>
Date: Wed, 2 Aug 2023 14:14:09 +0200
Subject: [PATCH] add `CmpToZero` and `MagnitudeSquared` traits

---
 src/gjk.rs            |  7 ++----
 src/math/glam_0_24.rs | 10 ---------
 src/math/mod.rs       | 52 ++++++++++++++++++++++++++++++++++++++-----
 3 files changed, 48 insertions(+), 21 deletions(-)

diff --git a/src/gjk.rs b/src/gjk.rs
index f545e99..78b87b8 100644
--- a/src/gjk.rs
+++ b/src/gjk.rs
@@ -2,10 +2,7 @@ use core::{cmp::Ordering, ops::Neg};
 
 use glam::Vec2;
 
-use crate::{
-    math::{Dot, IsNegative, Perp},
-    Support,
-};
+use crate::{math::*, Support};
 
 pub(crate) fn find_simplex_enclosing_origin(
     shape: &impl Support<Vec2, Vec2>,
@@ -110,7 +107,7 @@ impl Simplex<Vec2> {
 fn perp<V>(axis: V, direction: V) -> V
 where
     V: Copy + Perp + Neg<Output = V> + Dot,
-    <V as Dot>::Scalar: IsNegative,
+    <V as Dot>::Scalar: CmpToZero,
 {
     let perp = axis.perp();
     if perp.dot(direction).is_negative() {
diff --git a/src/math/glam_0_24.rs b/src/math/glam_0_24.rs
index b47ddbc..86cba30 100644
--- a/src/math/glam_0_24.rs
+++ b/src/math/glam_0_24.rs
@@ -9,16 +9,6 @@ impl Dot for Vec2 {
     }
 }
 
-impl Zero for Vec2 {
-    const ZERO: Self = Vec2::ZERO;
-}
-
-impl IsNegative for f32 {
-    fn is_negative(&self) -> bool {
-        *self < 0.0
-    }
-}
-
 impl Perp for Vec2 {
     fn perp(self) -> Self {
         Vec2::perp(self)
diff --git a/src/math/mod.rs b/src/math/mod.rs
index 83c271d..a01a34c 100644
--- a/src/math/mod.rs
+++ b/src/math/mod.rs
@@ -6,14 +6,54 @@ pub(crate) trait Dot {
     fn dot(self, other: Self) -> Self::Scalar;
 }
 
-pub(crate) trait Zero {
-    const ZERO: Self;
-}
-
-pub(crate) trait IsNegative {
-    fn is_negative(&self) -> bool;
+pub(crate) trait CmpToZero: Copy {
+    fn is_negative(self) -> bool;
+    fn is_zero(self) -> bool;
+    fn is_positive(self) -> bool;
 }
 
 pub(crate) trait Perp {
     fn perp(self) -> Self;
 }
+
+pub(crate) trait MagnitudeSquared {
+    type Scalar;
+    fn magnitude_squared(self) -> Self::Scalar;
+}
+
+impl<V: Dot + Copy> MagnitudeSquared for V {
+    type Scalar = <V as Dot>::Scalar;
+    fn magnitude_squared(self) -> Self::Scalar {
+        self.dot(self)
+    }
+}
+
+impl CmpToZero for f32 {
+    fn is_negative(self) -> bool {
+        self < 0.0
+    }
+
+    fn is_zero(self) -> bool {
+        self == 0.0
+    }
+
+    fn is_positive(self) -> bool {
+        self > 0.0
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use approx::assert_ulps_eq;
+    use rstest::rstest;
+
+    #[rstest]
+    #[case([0.0, 0.0], 0.0)]
+    #[case([2.0, 3.0], 13.0)]
+    #[case([3.0, 4.0], 25.0)]
+    #[case([4.0, 3.0], 25.0)]
+    fn test_magnitude_squared(#[case] vector: [f32; 2], #[case] expected: f32) {
+        assert_ulps_eq!(vector.magnitude_squared(), expected);
+    }
+}