chap 9.3

1 files changed, 19 insertions, 0 deletions

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