From b976ce98be7275bf92e01f6c86bf2b694530481e Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Thu, 13 Jun 2024 13:24:53 +0100
Subject: Done C10, Materials

---
 lib/hittable.rb | 16 +++++++---------
 lib/material.rb | 38 ++++++++++++++++++++++++++++++++++++++
 lib/ray.rb      |  7 +++++--
 lib/vec3.rb     |  8 ++++++++
 rtiaw           | 14 +++++++++++---
 5 files changed, 69 insertions(+), 14 deletions(-)
 create mode 100644 lib/material.rb

diff --git a/lib/hittable.rb b/lib/hittable.rb
index c84764f..facdd14 100644
--- a/lib/hittable.rb
+++ b/lib/hittable.rb
@@ -1,16 +1,13 @@
 class HitRecord
-  def initialize(point, t, ray, out_normal)
+  def initialize(point, t, ray, out_normal, material)
     @point = point
     @t = t
-    set_face_normal(ray, out_normal)
-  end
-
-  attr_accessor :point, :normal, :t
-
-  def set_face_normal(ray, out_normal)
     front_face = ray.direction.dot(out_normal) < 0
     @normal = front_face ? out_normal : -out_normal
+    @material = material
   end
+
+  attr_accessor :point, :normal, :t, :material
 end
 
 class Hittable
@@ -48,9 +45,10 @@ class Hittables < Hittable
 end
 
 class Sphere < Hittable
-  def initialize(ox, oy, oz, radius = 1)
+  def initialize(ox, oy, oz, radius = 1, material)
     @centre = Point.new(ox, oy, oz)
     @radius = radius
+    @material = material
   end
 
   attr_reader :centre, :radius
@@ -76,6 +74,6 @@ class Sphere < Hittable
     t = root
     p = ray.at(t)
     o_n = (p - @centre) / @radius
-    HitRecord.new(p, t, ray, o_n)
+    HitRecord.new(p, t, ray, o_n, @material)
   end
 end
diff --git a/lib/material.rb b/lib/material.rb
new file mode 100644
index 0000000..c935147
--- /dev/null
+++ b/lib/material.rb
@@ -0,0 +1,38 @@
+class Material
+  def initialize(r, g, b)
+    @albedo = Colour.new(r, g, b)
+  end
+
+  def attenuation
+    @albedo
+  end
+
+  def scatter(ray, record)
+    nil
+  end
+end
+
+class Lambertian < Material
+  def scatter(ray, record)
+    scat = record.normal + Vec3.random_unit
+    scat = rec.normal if scat.near_zero?
+    Ray.new(record.point, scat)
+  end
+end
+
+class Metal < Material
+  def initialize(r, g, b, fuzz)
+    @fuzz = fuzz < 1 ? fuzz : 1
+    super(r, g, b)
+  end
+
+  def scatter(ray, record)
+    refl = ray.direction.reflect(record.normal)
+    refl = refl.unit + (Vec3.random_unit * @fuzz)
+    if refl.dot(record.normal) > 0
+      Ray.new(record.point, refl)
+    else
+      nil
+    end
+  end
+end
diff --git a/lib/ray.rb b/lib/ray.rb
index eb6038c..1285158 100644
--- a/lib/ray.rb
+++ b/lib/ray.rb
@@ -14,8 +14,11 @@ class Ray
     return Colour.new if depth <= 0
 
     if rec = world.hit(self, Interval.new(0.0001, Float::INFINITY))
-      dir = rec.normal + Vec3.random_unit
-      return Ray.new(rec.point, dir).colour(world, depth - 1) * 0.5
+      if scat = rec.material.scatter(self, rec)
+        return scat.colour(world, depth - 1) * rec.material.attenuation
+      else
+        return Colour.new(0,0,0)
+      end
     end
 
     unit_dir = direction.unit
diff --git a/lib/vec3.rb b/lib/vec3.rb
index 08cbf69..3069b65 100644
--- a/lib/vec3.rb
+++ b/lib/vec3.rb
@@ -56,10 +56,18 @@ class Vec3
     self / mag
   end
 
+  def reflect(normal)
+    self - normal * dot(normal) * 2
+  end
+
   def in_unit_sphere?
     mag_sqr < 1
   end
 
+  def near_zero?(s = 1e-8)
+    @x.abs < s && @y.abs < s && @z.abs < s
+  end
+
   def to_s
     "{#{@x}, #{@y}, #{@z}}"
   end
diff --git a/rtiaw b/rtiaw
index 82e4303..71b4fbd 100755
--- a/rtiaw
+++ b/rtiaw
@@ -1,15 +1,23 @@
 #!/usr/bin/env ruby
 
-$LOAD_PATH.unshift File.dirname(__FILE__) + '/lib'
+$LOAD_PATH.unshift(File.join(File.dirname(__FILE__), 'lib'))
 require 'interval'
 require 'vec3'
 require 'ray'
 require 'hittable'
 require 'camera'
+require 'material'
+
+mat_ground = Lambertian.new(0.8, 0.8, 0.0)
+mat_centre = Lambertian.new(0.1, 0.2, 0.5)
+mat_left = Metal.new(0.8, 0.8, 0.8, 0.3)
+mat_right = Metal.new(0.8, 0.6, 0.2, 1.0)
 
 world = Hittables.new
-world << Sphere.new(0,0,-1, 0.5)
-world << Sphere.new(0,-100.5,-1, 100)
+world << Sphere.new(0, -100.5, -1,    100,    mat_ground)
+world << Sphere.new(0,      0, -1,    0.5,    mat_centre)
+world << Sphere.new(-1,     0, -1,    0.5,    mat_left)
+world << Sphere.new(1,      0, -1,    0.5,    mat_right)
 
 camera = Camera.new(400, 16.0 / 9)
 camera.render(world)
-- 
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