1 files changed, 81 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