From c16ba06a53c4a023f834650ee141e7a72be0eda7 Mon Sep 17 00:00:00 2001
From: Bill Thiede <git@xinu.tv>
Date: Sat, 8 Sep 2018 21:53:15 -0700
Subject: [PATCH] Normal shading of sphere.

Doesn't quite work right.
---
 rtiow/src/bin/tracer_norm_shade.rs | 51 ++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 rtiow/src/bin/tracer_norm_shade.rs

diff --git a/rtiow/src/bin/tracer_norm_shade.rs b/rtiow/src/bin/tracer_norm_shade.rs
new file mode 100644
index 0000000..7f65e77
--- /dev/null
+++ b/rtiow/src/bin/tracer_norm_shade.rs
@@ -0,0 +1,51 @@
+extern crate rtiow;
+
+use rtiow::ray::Ray;
+use rtiow::vec3::dot;
+use rtiow::vec3::Vec3;
+
+fn hit_sphere(center: Vec3, radius: f32, r: Ray) -> f32 {
+    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;
+    if discriminant < 0. {
+        return -1.;
+    }
+    -b - discriminant.sqrt() / (2. * a)
+}
+
+fn color(r: Ray) -> Vec3 {
+    let t = hit_sphere(Vec3::new(0., 0., -1.), 0.5, r);
+    if t > 0. {
+        let n = (r.point_at_parameter(t) - Vec3::new(0., 0., -1.)).unit_vector();
+        return (n + 1.) * 0.5;
+    }
+    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(())
+}