Add scale_around_center method to BoundingVolume trait (#12142)

# Objective

Add a `scale_around_center` method to the `BoundingVolume` trait, as per
#12130.

## Solution

Added `scale_around_center` to the `BoundingVolume` trait, implemented
in `Aabb2d`, `Aabb3d`, `BoundingCircle`, and `BoundingSphere` (with
tests).

crates/bevy_math/src/bounding/bounded2d/mod.rs

@@ -152,6 +152,16 @@ impl BoundingVolume for Aabb2d {
         b
     }
 
+    #[inline(always)]
+    fn scale_around_center(&self, scale: Self::HalfSize) -> Self {
+        let b = Self {
+            min: self.center() - (self.half_size() * scale),
+            max: self.center() + (self.half_size() * scale),
+        };
+        debug_assert!(b.min.x <= b.max.x && b.min.y <= b.max.y);
+        b
+    }
+
     /// Transforms the bounding volume by first rotating it around the origin and then applying a translation.
     ///
     /// The result is an Axis-Aligned Bounding Box that encompasses the rotated shape.
@@ -352,6 +362,19 @@ mod aabb2d_tests {
         assert!(!shrunk.contains(&a));
     }
 
+    #[test]
+    fn scale_around_center() {
+        let a = Aabb2d {
+            min: Vec2::NEG_ONE,
+            max: Vec2::ONE,
+        };
+        let scaled = a.scale_around_center(Vec2::splat(2.));
+        assert!((scaled.min - Vec2::splat(-2.)).length() < std::f32::EPSILON);
+        assert!((scaled.max - Vec2::splat(2.)).length() < std::f32::EPSILON);
+        assert!(!a.contains(&scaled));
+        assert!(scaled.contains(&a));
+    }
+
     #[test]
     fn transform() {
         let a = Aabb2d {
@@ -546,6 +569,12 @@ impl BoundingVolume for BoundingCircle {
         Self::new(self.center, self.radius() - amount)
     }
 
+    #[inline(always)]
+    fn scale_around_center(&self, scale: Self::HalfSize) -> Self {
+        debug_assert!(scale >= 0.);
+        Self::new(self.center, self.radius() * scale)
+    }
+
     #[inline(always)]
     fn translate_by(&mut self, translation: Self::Translation) {
         self.center += translation;
@@ -658,6 +687,15 @@ mod bounding_circle_tests {
         assert!(!shrunk.contains(&a));
     }
 
+    #[test]
+    fn scale_around_center() {
+        let a = BoundingCircle::new(Vec2::ONE, 5.);
+        let scaled = a.scale_around_center(2.);
+        assert!((scaled.radius() - 10.).abs() < std::f32::EPSILON);
+        assert!(!a.contains(&scaled));
+        assert!(scaled.contains(&a));
+    }
+
     #[test]
     fn transform() {
         let a = BoundingCircle::new(Vec2::ONE, 5.0);

crates/bevy_math/src/bounding/bounded3d/mod.rs

@@ -147,6 +147,16 @@ impl BoundingVolume for Aabb3d {
         b
     }
 
+    #[inline(always)]
+    fn scale_around_center(&self, scale: Self::HalfSize) -> Self {
+        let b = Self {
+            min: self.center() - (self.half_size() * scale),
+            max: self.center() + (self.half_size() * scale),
+        };
+        debug_assert!(b.min.x <= b.max.x && b.min.y <= b.max.y);
+        b
+    }
+
     /// Transforms the bounding volume by first rotating it around the origin and then applying a translation.
     ///
     /// The result is an Axis-Aligned Bounding Box that encompasses the rotated shape.
@@ -348,6 +358,19 @@ mod aabb3d_tests {
         assert!(!shrunk.contains(&a));
     }
 
+    #[test]
+    fn scale_around_center() {
+        let a = Aabb3d {
+            min: Vec3::NEG_ONE,
+            max: Vec3::ONE,
+        };
+        let scaled = a.scale_around_center(Vec3::splat(2.));
+        assert!((scaled.min - Vec3::splat(-2.)).length() < std::f32::EPSILON);
+        assert!((scaled.max - Vec3::splat(2.)).length() < std::f32::EPSILON);
+        assert!(!a.contains(&scaled));
+        assert!(scaled.contains(&a));
+    }
+
     #[test]
     fn transform() {
         let a = Aabb3d {
@@ -549,6 +572,12 @@ impl BoundingVolume for BoundingSphere {
         }
     }
 
+    #[inline(always)]
+    fn scale_around_center(&self, scale: Self::HalfSize) -> Self {
+        debug_assert!(scale >= 0.);
+        Self::new(self.center, self.radius() * scale)
+    }
+
     #[inline(always)]
     fn translate_by(&mut self, translation: Self::Translation) {
         self.center += translation;
@@ -663,6 +692,15 @@ mod bounding_sphere_tests {
         assert!(!shrunk.contains(&a));
     }
 
+    #[test]
+    fn scale_around_center() {
+        let a = BoundingSphere::new(Vec3::ONE, 5.);
+        let scaled = a.scale_around_center(2.);
+        assert!((scaled.radius() - 10.).abs() < std::f32::EPSILON);
+        assert!(!a.contains(&scaled));
+        assert!(scaled.contains(&a));
+    }
+
     #[test]
     fn transform() {
         let a = BoundingSphere::new(Vec3::ONE, 5.0);

crates/bevy_math/src/bounding/mod.rs

@@ -48,6 +48,9 @@ pub trait BoundingVolume: Sized {
     /// Decreases the size of the bounding volume in each direction by the given amount.
     fn shrink(&self, amount: Self::HalfSize) -> Self;
 
+    /// Scale the size of the bounding volume around its center by the given amount
+    fn scale_around_center(&self, scale: Self::HalfSize) -> Self;
+
     /// Transforms the bounding volume by first rotating it around the origin and then applying a translation.
     fn transformed_by(
         mut self,