Add sphere.

Move original tracer1 to tracer_blue_sky and create new tracer as
tracer_red_dot.

rtiow/src/bin/tracer_blue_sky.rs

@@ -1,9 +1,22 @@
 extern crate rtiow;
 
 use rtiow::ray::Ray;
+use rtiow::vec3::dot;
 use rtiow::vec3::Vec3;
 
+fn hit_sphere(center: Vec3, radius: f32, r: Ray) -> bool {
+    let oc = r.origin() - center;
+    let a = dot(r.direction(), r.direction());
+    let b = 2. * dot(oc, r.direction());
+    let c = dot(oc, oc) - radius * radius;
+    let discriminant = b * b - 4. * a * c;
+    discriminant > 0.
+}
+
 fn color(r: Ray) -> Vec3 {
+    if hit_sphere(Vec3::new(0., 0., -1.), 0.5, r) {
+        return Vec3::new(1., 0., 0.);
+    }
     let unit_direction = r.direction().unit_vector();
     let t = 0.5 * (unit_direction.y + 1.);
     Vec3::new(1., 1., 1.) * (1. - t) + Vec3::new(0.5, 0.7, 1.) * t

rtiow/src/bin/tracer_red_dot.rs

@@ -0,0 +1,46 @@
+extern crate rtiow;
+
+use rtiow::ray::Ray;
+use rtiow::vec3::dot;
+use rtiow::vec3::Vec3;
+
+fn hit_sphere(center: Vec3, radius: f32, r: Ray) -> bool {
+    let oc = r.origin() - center;
+    let a = dot(r.direction(), r.direction());
+    let b = 2. * dot(oc, r.direction());
+    let c = dot(oc, oc) - radius * radius;
+    let discriminant = b * b - 4. * a * c;
+    discriminant > 0.
+}
+
+fn color(r: Ray) -> Vec3 {
+    if hit_sphere(Vec3::new(0., 0., -1.), 0.5, r) {
+        return Vec3::new(1., 0., 0.);
+    }
+    let unit_direction = r.direction().unit_vector();
+    let t = 0.5 * (unit_direction.y + 1.);
+    Vec3::new(1., 1., 1.) * (1. - t) + Vec3::new(0.5, 0.7, 1.) * t
+}
+
+fn main() -> Result<(), std::io::Error> {
+    let nx = 200;
+    let ny = 100;
+    println!("P3\n{} {}\n255", nx, ny);
+    let lower_left_corner = Vec3::new(-2., -1., -1.);
+    let horizontal = Vec3::new(4., 0., 0.);
+    let vertical = Vec3::new(0., 2., 0.);
+    let origin: Vec3 = Default::default();
+    for j in (0..ny).rev() {
+        for i in 0..nx {
+            let u = i as f32 / nx as f32;
+            let v = j as f32 / ny as f32;
+            let r = Ray::new(origin, lower_left_corner + horizontal * u + vertical * v);
+            let col = color(r);
+            let ir = (255.99 * col[0]) as u32;
+            let ig = (255.99 * col[1]) as u32;
+            let ib = (255.99 * col[2]) as u32;
+            println!("{} {} {}", ir, ig, ib);
+        }
+    }
+    Ok(())
+}

rtiow/src/ray.rs

@@ -1,6 +1,6 @@
 use vec3::Vec3;
 
-#[derive(Default)]
+#[derive(Copy, Clone, Default)]
 pub struct Ray {
     a: Vec3,
     b: Vec3,