stocking

commit 3193d1343701297c741155d80e7e7a0106a0c1c8
parent 01ef5128cb055813bc648c8f36374f2a041c406e
Author: Bradley Gannon <bradley@bradleygannon.com>
Date:   Sat, 13 Dec 2025 15:48:28 -0500

Add a sphere

Complete Chapter 5

Diffstat:
M
src/color.rs
 | 
2
+-
M
src/main.rs
 | 
13
++++++++++++-
M
src/ray.rs
 | 
14
++++++--------
M
src/vec3.rs
 | 
2
+-

4 files changed, 20 insertions(+), 11 deletions(-)
diff --git a/src/color.rs b/src/color.rs
@@ -1,6 +1,6 @@
 use std::ops::{Add, Mul};
 
-#[derive(Clone, Copy, Debug, Default)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, PartialOrd)]
 pub struct Color {
     red: f64,
     green: f64,
diff --git a/src/main.rs b/src/main.rs
@@ -4,6 +4,15 @@ mod color;
 mod ray;
 mod vec3;
 
+fn hit_sphere(center: Vec3, radius: f64, r: Ray) -> bool {
+    let oc = center - r.origin();
+    let a = r.direction().dot(&r.direction());
+    let b = -2. * r.direction().dot(&oc);
+    let c = oc.dot(&oc) - radius * radius;
+    let discriminant = b * b - 4. * a * c;
+    discriminant >= 0.
+}
+
 struct Image {
     data: Vec<Vec<Color>>,
 }
@@ -69,7 +78,9 @@ fn main() {
                 pixel_origin + (i as f64 * pixel_delta_u) + (j as f64 * pixel_delta_v);
             let ray_direction = pixel_center - CAMERA_CENTER;
             let ray = Ray::new(CAMERA_CENTER, ray_direction);
-            let color = {
+            let color = if hit_sphere(Vec3::new(0., 0., -1.), 0.5, ray) {
+                Color::new(1., 0., 0.)
+            } else {
                 let unit_direction = ray.direction().unit();
                 let a = 0.5 * (unit_direction.y() + 1.);
                 (1. - a) * Color::new(1., 1., 1.) + a * Color::new(0.5, 0.7, 1.)
diff --git a/src/ray.rs b/src/ray.rs
@@ -1,20 +1,18 @@
 use crate::vec3::Vec3;
 
+#[derive(Clone, Copy, Debug, Default, PartialEq, PartialOrd)]
 pub struct Ray {
-    _origin: Vec3,
+    origin: Vec3,
     direction: Vec3,
 }
 
 impl Ray {
     pub const fn new(origin: Vec3, direction: Vec3) -> Self {
-        Ray {
-            _origin: origin,
-            direction,
-        }
+        Ray { origin, direction }
     }
 
-    pub const fn _origin(&self) -> Vec3 {
-        self._origin
+    pub const fn origin(&self) -> Vec3 {
+        self.origin
     }
 
     pub const fn direction(&self) -> Vec3 {
@@ -22,6 +20,6 @@ impl Ray {
     }
 
     pub fn _at(&self, t: f64) -> Vec3 {
-        self._origin + t * self.direction
+        self.origin + t * self.direction
     }
 }
diff --git a/src/vec3.rs b/src/vec3.rs
@@ -3,7 +3,7 @@ use std::{
     ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Neg, Sub},
 };
 
-#[derive(Copy, Clone, Debug, Default)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, PartialOrd)]
 pub struct Vec3 {
     x: f64,
     y: f64,