Initial Commit (Up to Chapter 7)

4 files changed, 187 insertions, 0 deletions

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