From 1bc4829392b3c91737fbe4ddccd81098ac9d8a12 Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Wed, 12 Jun 2024 22:51:25 +0100
Subject: chap 9.3

---
 lib/camera.rb |  5 +++--
 lib/ray.rb    |  9 ++++++---
 lib/vec3.rb   | 19 +++++++++++++++++++
 3 files changed, 28 insertions(+), 5 deletions(-)

(limited to 'lib')

diff --git a/lib/camera.rb b/lib/camera.rb
index f8721bb..6a3b190 100644
--- a/lib/camera.rb
+++ b/lib/camera.rb
@@ -1,8 +1,9 @@
 class Camera
-  def initialize(width = 100, aspect = 1.0, aliasing = 10)
+  def initialize(width = 100, aspect = 1.0, aliasing = 10, depth = 10)
     @width = width
     @aspect = aspect
     @aliasing = aliasing
+    @depth = depth
 
     # Height
     @height = (@width / @aspect).to_i
@@ -40,7 +41,7 @@ class Camera
       @width.times do |col|
         p_colour = Colour.new
         @aliasing.times do
-          p_colour += get_ray(row, col).colour(world)
+          p_colour += get_ray(row, col).colour(world, @depth)
         end
         puts (p_colour / @aliasing).to_ppm
       end
diff --git a/lib/ray.rb b/lib/ray.rb
index 47f2b26..c1679a5 100644
--- a/lib/ray.rb
+++ b/lib/ray.rb
@@ -10,9 +10,12 @@ class Ray
     @origin + (@direction * time)
   end
 
-  def colour(world)
-    if rec = world.hit(self, Interval.new(0, Float::INFINITY))
-      return (Colour.new(1,1,1) + rec.normal) * 0.5
+  def colour(world, depth)
+    return Colour.new if depth <= 0
+
+    if rec = world.hit(self, Interval.new(0.0001, Float::INFINITY))
+      dir = Vec3.random_unit(rec.normal)
+      return Ray.new(rec.point, dir).colour(world, depth - 1) * 0.5
     end
 
     unit_dir = direction.unit
diff --git a/lib/vec3.rb b/lib/vec3.rb
index b9a5a73..e24229a 100644
--- a/lib/vec3.rb
+++ b/lib/vec3.rb
@@ -56,9 +56,28 @@ class Vec3
     self / mag
   end
 
+  def in_unit_sphere?
+    mag_sqr < 1
+  end
+
   def to_s
     "{#{@x}, #{@y}, #{@z}}"
   end
+
+  def self.random(min = 0, max = 1)
+    interval = Interval.new(min.to_f, max.to_f)
+    Vec3.new(interval.sample, interval.sample, interval.sample)
+  end
+
+  def self.random_unit(normal = nil)
+    p = nil
+    while p.nil?
+      c = Vec3.random
+      p = c.unit if c.in_unit_sphere?
+    end
+
+    normal.nil? || p.dot(normal) > 0 ? p : -p
+  end
 end
 
 class Point < Vec3; end
-- 
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