Add methods intersect_plane and get_point to Ray (#6179)

Co-authored-by: devil-ira <justthecooldude@gmail.com>

crates/bevy_math/src/ray.rs

@@ -6,6 +6,59 @@ use crate::Vec3;
 pub struct Ray {
     /// The origin of the ray.
     pub origin: Vec3,
-    /// The direction of the ray.
+    /// A normalized vector representing the direction of the ray.
     pub direction: Vec3,
 }
+
+impl Ray {
+    /// Returns the distance to the plane if the ray intersects it.
+    #[inline]
+    pub fn intersect_plane(&self, plane_origin: Vec3, plane_normal: Vec3) -> Option<f32> {
+        let denominator = plane_normal.dot(self.direction);
+        if denominator.abs() > f32::EPSILON {
+            let distance = (plane_origin - self.origin).dot(plane_normal) / denominator;
+            if distance >= f32::EPSILON {
+                return Some(distance);
+            }
+        }
+        None
+    }
+
+    /// Retrieve a point at the given distance along the ray.
+    #[inline]
+    pub fn get_point(&self, distance: f32) -> Vec3 {
+        self.origin + self.direction * distance
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn intersects_plane() {
+        let ray = Ray {
+            origin: Vec3::ZERO,
+            direction: Vec3::Z,
+        };
+
+        // Orthogonal, and test that plane_normal direction doesn't matter
+        assert_eq!(Some(1.), ray.intersect_plane(Vec3::Z, Vec3::Z));
+        assert_eq!(Some(1.), ray.intersect_plane(Vec3::Z, Vec3::NEG_Z));
+        assert_eq!(None, ray.intersect_plane(Vec3::NEG_Z, Vec3::Z));
+        assert_eq!(None, ray.intersect_plane(Vec3::NEG_Z, Vec3::NEG_Z));
+
+        // Diagonal
+        assert_eq!(Some(1.), ray.intersect_plane(Vec3::Z, Vec3::ONE));
+        assert_eq!(None, ray.intersect_plane(Vec3::NEG_Z, Vec3::ONE));
+
+        // Parralel
+        assert_eq!(None, ray.intersect_plane(Vec3::X, Vec3::X));
+
+        // Parralel with simulated rounding error
+        assert_eq!(
+            None,
+            ray.intersect_plane(Vec3::X, Vec3::X + Vec3::Z * f32::EPSILON)
+        );
+    }
+}