first normal shaded sphere

src/main.rs

@@ -9,24 +9,31 @@ use crate::{
     ray::*
 };
 
-fn hit_sphere(center: &Point3, radius: f64, r: &Ray) -> bool {
+fn hit_sphere(center: &Point3, radius: f64, r: &Ray) -> f64 {
     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
+    if discriminant < 0.0 {
+        -1.0
+    } else {
+        (-b - discriminant.sqrt()) / (2.0 * a)
+    }
 }
 
 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 t = hit_sphere(&Point3::new(0.0, 0.0, -1.0), 0.5, r);
+    
+    if t > 0.0 {
+        let n = (r.at(t) - Vec3::new(0.0, 0.0, -1.0)).unit_vector();
+        return 0.5 * Color::new(n.x() + 1.0, n.y() + 1.0, n.z() + 1.0);
     }
 
     let unit_direction: Vec3 = r.direction().unit_vector();
     let t = 0.5 * (unit_direction.y() + 1.0);
-    //println!("{}", t);
+
     ((1.0 - t) * Color::new(1.0, 1.0, 1.0)) + (t * Color::new(0.5, 0.7, 1.0))
 }
 
@@ -53,12 +60,10 @@ fn main() {
 
     writeln!(file, "P3\n{image_width} {image_height}\n255").expect("Error while writing Magic Byte");
 
-    for j in (0..image_width).rev() {
-        //println!("{}", j);
-        //println!("Rows remaining: {j}");
+    for j in 0..image_width {
+        println!("Rows remaining: {}", image_width - j);
         write!(file, "\n").expect("grr");
-        for i in (0..image_height).rev() {
-            //println!("{}", i);
+        for i in 0..image_height {
             let u: f64 = i as f64 / image_width as f64;
             let v: f64 = j as f64 / image_height as f64;
             let r = Ray::new(origin, lower_left_corner + u * horizontal + v * vertical - origin);