first sphere

src/main.rs

@@ -9,7 +9,21 @@ use crate::{
     ray::*
 };
 
+fn hit_sphere(center: &Point3, radius: f64, r: &Ray) -> bool {
+    let oc = r.origin() - *center;
+    let a = r.direction().dot(&r.direction());
+    let b = 2.0 * oc.dot(&r.direction());
+    let c = oc.dot(&oc) - radius*radius;
+    let discriminant = b*b - 4.0*a*c;
+
+    discriminant > 0.0
+}
+
 fn ray_color(r: &Ray) -> Color {
+    if hit_sphere(&Point3::new(0.0, 0.0, -1.0), 0.5, r) {
+        return Color::new(1.0, 0.0, 0.0);
+    }
+
     let unit_direction: Vec3 = r.direction().unit_vector();
     let t = 0.5 * (unit_direction.y() + 1.0);
     //println!("{}", t);