From df7c4a808d691e1d927047bb86aa9738780e694d Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Wed, 12 Jun 2024 17:37:40 +0100
Subject: Initial Commit (Up to Chapter 7)

---
 .gitignore      |  2 ++
 Makefile        | 10 +++++++
 Readme          |  6 +++++
 lib/hittable.rb | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/interval.rb | 20 ++++++++++++++
 lib/ray.rb      | 12 +++++++++
 lib/vec3.rb     | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 rtiaw           | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 8 files changed, 284 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 Readme
 create mode 100644 lib/hittable.rb
 create mode 100644 lib/interval.rb
 create mode 100644 lib/ray.rb
 create mode 100644 lib/vec3.rb
 create mode 100755 rtiaw

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..470cb69
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+*.swp
+out.ppm
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..3536afe
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,10 @@
+out.ppm: rtiaw $(wildcard lib/*.rb)
+	./$< > $@
+
+.phony: view clean
+
+view: out.ppm
+	eog out.ppm &
+
+clean:
+	rm -f out.ppm
diff --git a/Readme b/Readme
new file mode 100644
index 0000000..28343de
--- /dev/null
+++ b/Readme
@@ -0,0 +1,6 @@
+Ray Tracing in a Weekend in Ruby.
+
+I've made some decisions when porting it.
+Disagree with me if you like. That sounds like your problem.
+
+https://raytracing.github.io/books/RayTracingInOneWeekend.html
diff --git a/lib/hittable.rb b/lib/hittable.rb
new file mode 100644
index 0000000..80254d1
--- /dev/null
+++ b/lib/hittable.rb
@@ -0,0 +1,81 @@
+class HitRecord
+  def initialize(point, t, ray, out_normal)
+    @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
+  end
+end
+
+class Hittable
+  def hit(ray, trange)
+    nil
+  end
+end
+
+class Hittables < Hittable
+  def initialize
+    clear
+  end
+
+  def clear
+    @objects = []
+  end
+
+  def <<(object)
+    @objects << object
+  end
+
+  def hit(ray, trange)
+    rec = nil
+    closest = trange.max
+
+    @objects.each do |object|
+      if trec = object.hit(ray, Interval.new(trange.min, closest))
+        rec = trec
+        closest = trec.t
+      end
+    end
+
+    rec
+  end
+end
+
+class Sphere < Hittable
+  def initialize(ox, oy, oz, radius = 1)
+    @centre = Point.new(ox, oy, oz)
+    @radius = radius
+  end
+
+  attr_reader :centre, :radius
+
+  def hit(ray, trange)
+    oc = @centre - ray.origin
+    a = ray.direction.mag_sqr
+    h = ray.direction.dot(oc)
+    c = oc.mag_sqr - @radius ** 2
+    disc = h ** 2 - a * c
+    
+    return nil if disc < 0
+
+    sqrtd = disc ** 0.5
+    root = (h - sqrtd) / a
+    if !trange.surround?(root)
+      root = (h + sqrtd) / a
+      if !trange.surround?(root)
+        return nil
+      end
+    end
+
+    t = root
+    p = ray.at(t)
+    o_n = (p - @centre) / @radius
+    HitRecord.new(p, t, ray, o_n)
+  end
+end
diff --git a/lib/interval.rb b/lib/interval.rb
new file mode 100644
index 0000000..0aa787f
--- /dev/null
+++ b/lib/interval.rb
@@ -0,0 +1,20 @@
+class Interval
+  def initialize(min = Float::INFINITY, max = -Float::INFINITY)
+    @min = min
+    @max = max
+  end
+
+  attr_reader :min, :max
+
+  def size
+    @max - @min
+  end
+
+  def include?(x)
+    min <= x && x <= max
+  end
+
+  def surround?(x)
+    min < x && x < max
+  end
+end
diff --git a/lib/ray.rb b/lib/ray.rb
new file mode 100644
index 0000000..4d282cb
--- /dev/null
+++ b/lib/ray.rb
@@ -0,0 +1,12 @@
+class Ray
+  def initialize(origin = Point.new, direction = Vec3.new)
+    @origin = origin
+    @direction = direction
+  end
+
+  attr_reader :origin, :direction
+
+  def at(time)
+    @origin + (@direction * time)
+  end
+end
diff --git a/lib/vec3.rb b/lib/vec3.rb
new file mode 100644
index 0000000..6287813
--- /dev/null
+++ b/lib/vec3.rb
@@ -0,0 +1,74 @@
+class Vec3
+  def initialize(x = 0, y = 0, z = 0)
+    @x = x.to_f
+    @y = y.to_f
+    @z = z.to_f
+  end
+
+  attr_reader :x, :y, :z
+
+  def +(oth)
+    self.class.new(@x + oth.x, @y + oth.y, @z + oth.z)
+  end
+
+  def -@
+    self.class.new(-@x, -@y, -@z)
+  end
+
+  def -(oth)
+    self + -oth
+  end
+
+  def *(oth)
+    if oth.is_a?(Vec3)
+      self.class.new(@x * oth.x, @y * oth.y, @z * oth.z)
+    else
+      self.class.new(@x * oth, @y * oth, @z * oth)
+    end
+  end
+
+  def /(oth)
+    self * (1.0 / oth)
+  end
+
+  def dot(oth)
+    v = self * oth
+    v.x + v.y + v.z
+  end
+
+  def cross(oth)
+    self.class.new(
+      @y * oth.z - @z * oth.y,
+      @z * oth.x - @x * oth.z,
+      @x * oth.y - @y * oth.x
+    )
+  end
+
+  def mag_sqr
+    @x ** 2 + @y ** 2 + @z ** 2
+  end
+
+  def mag
+    mag_sqr ** 0.5
+  end
+
+  def unit
+    self / mag
+  end
+
+  def to_s
+    "{#{@x}, #{@y}, #{@z}}"
+  end
+end
+
+class Point < Vec3; end
+
+class Colour < Vec3
+  def r; @x; end
+  def g; @y; end
+  def b; @z; end
+
+  def to_ppm
+    "%3d %3d %3d" % [(r * 255.999).to_i, (g * 255.999).to_i, (b * 255.999).to_i]
+  end
+end
diff --git a/rtiaw b/rtiaw
new file mode 100755
index 0000000..5fb7e5a
--- /dev/null
+++ b/rtiaw
@@ -0,0 +1,79 @@
+#!/usr/bin/env ruby
+
+start = Time.now.to_f
+
+$LOAD_PATH.unshift File.dirname(__FILE__) + '/lib'
+require 'interval'
+require 'vec3'
+require 'ray'
+require 'hittable'
+
+def ray_colour(ray, world)
+  if rec = world.hit(ray, Interval.new(0, Float::INFINITY))
+    return (Colour.new(1,1,1) + rec.normal) * 0.5
+  end
+
+  unit_dir = ray.direction.unit
+  a = (unit_dir.y + 1) / 2
+  Colour.new(1.0, 1.0, 1.0) * (1-a) + Colour.new(0.5, 0.7, 1.0) * a
+end
+
+# Define image
+width = 400
+aspect = 16.0 / 9
+max = 255
+
+# Calculate height
+height = (width / aspect).to_i
+height = height < 1 ? 1 : height
+
+# World
+world = Hittables.new
+world << Sphere.new(0,0,-1, 0.5)
+world << Sphere.new(0,-100.5,-1, 100)
+
+# Camera
+c_focallength = 1.0
+c_centre = Point.new(0,0,0)
+
+# Viewport
+v_height = 2.0
+v_width = v_height * width.to_f / height
+v_u = Vec3.new(v_width, 0, 0)
+v_v = Vec3.new(0, -v_height, 0)
+
+# Pixel deltas
+pd_u = v_u / width
+pd_v = v_v / height
+
+# Upper left pixel
+v_upperleft = c_centre -
+              Vec3.new(0, 0, c_focallength) -
+              v_u / 2 -
+              v_v / 2
+p_00loc = v_upperleft +
+          (pd_u + pd_v) / 2
+
+puts <<-EOH
+P3
+#{width} #{height}
+#{max}
+EOH
+
+height.times do |row|
+  $stderr.print "Scanlines remaining: %4d" % (height - row)
+  width.times do |col|
+    p_centre = p_00loc + (pd_u * col) + (pd_v * row)
+    ray_dir = p_centre - c_centre
+    ray = Ray.new(c_centre, ray_dir)
+
+    p_colour = ray_colour(ray, world)
+    puts p_colour.to_ppm
+  end
+  puts
+end
+
+finish = Time.now.to_f
+took = finish - start
+
+$stderr.puts "Done. Took %4.2f seconds. " % took
-- 
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