2 files changed, 11 insertions(+), 9 deletions(-)

M src/main.rs
M src/vec3.rs

@@ 6,14 6,16 @@ use ray::*;
 
 fn hit_sphere(center: &Point3, radius: f64, r: &Ray) -> f64 {
     let oc = r.origin() - *center;
-    let a = dot(&r.direction(), &r.direction());
-    let b = 2.0 * dot(&oc, &r.direction());
-    let c = dot(&oc, &oc) - radius*radius;
-    let discriminant = b*b - 4f64*a*c;
+    let a = r.direction().length_squared();
+    let half_b = dot(&oc, &r.direction());
+    let c = oc.length_squared() - radius*radius;
+    let discriminant = half_b*half_b - a*c;
+
+
     if discriminant < 0.0 {
         -1.0
     } else {
-        (-b - discriminant.sqrt() ) / (2.0*a)
+        (-half_b - discriminant.sqrt() ) / a
     }
 }
 

@@ 21,11 21,11 @@ impl Vec3 {
         self.e[2]
     }
 
-    pub fn lenght(&self) -> f64 {
-        self.lenght_squared().sqrt()
+    pub fn length(&self) -> f64 {
+        self.length_squared().sqrt()
     }
 
-    pub fn lenght_squared(&self) -> f64 {
+    pub fn length_squared(&self) -> f64 {
         self.e[0] * self.e[0] + self.e[1] * self.e[1] + self.e[2] * self.e[2]
     }
 }


@@ 160,7 160,7 @@ pub fn cross(u: &Vec3, v: &Vec3) -> Vec3 {
 }
 
 pub fn unit_vector(v: Vec3) -> Vec3 {
-    v / v.lenght()
+    v / v.length()
 }
 
 pub fn write_color(out: &mut impl std::io::Write, pixel_color: Color) {