4 files changed, 91 insertions, 3 deletions

diff --git a/lib/camera.rb b/lib/camera.rb
new file mode 100644
index 0000000..f8721bb
--- /dev/null
+++ b/lib/camera.rb
@@ -0,0 +1,63 @@
+class Camera
+  def initialize(width = 100, aspect = 1.0, aliasing = 10)
+    @width = width
+    @aspect = aspect
+    @aliasing = aliasing
+
+    # Height
+    @height = (@width / @aspect).to_i
+    @height = @height < 1 ? 1 : @height
+
+    # 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 - v_u / 2 - v_v / 2 -
+                  Vec3.new(0, 0, c_focallength)
+    @p00_loc = v_upperleft + (@pd_u + @pd_v) / 2
+  end
+
+  def render(world)
+    start = Time.now.to_f
+
+    puts "P3"
+    puts "#{@width} #{@height}"
+    puts "255"
+
+    @height.times do |row|
+      $stderr.print "Scanlines remaining: %4d" % (@height - row)
+      @width.times do |col|
+        p_colour = Colour.new
+        @aliasing.times do
+          p_colour += get_ray(row, col).colour(world)
+        end
+        puts (p_colour / @aliasing).to_ppm
+      end
+      puts
+    end
+
+    finish = Time.now.to_f
+    took = finish - start
+
+    $stderr.puts "Done. Took %4.2f seconds. " % took
+  end
+
+  def get_ray(row, col)
+    p_sample = @p00_loc +
+               @pd_u * (col + rand - 0.5) +
+               @pd_v * (row + rand - 0.5)
+
+    Ray.new(@c_centre, p_sample - @c_centre)
+  end
+end
diff --git a/lib/interval.rb b/lib/interval.rb
index 0aa787f..3ba7e09 100644
--- a/lib/interval.rb
+++ b/lib/interval.rb
@@ -1,7 +1,7 @@
 class Interval
   def initialize(min = Float::INFINITY, max = -Float::INFINITY)
-    @min = min
-    @max = max
+    @min = min.to_f
+    @max = max.to_f
   end
 
   attr_reader :min, :max
@@ -17,4 +17,14 @@ class Interval
   def surround?(x)
     min < x && x < max
   end
+
+  def sample
+    rand(@min...@max)
+  end
+
+  def clamp(x)
+    return @min if x < @min
+    return @max if x > @max
+    x
+  end
 end
diff --git a/lib/ray.rb b/lib/ray.rb
index 4d282cb..47f2b26 100644
--- a/lib/ray.rb
+++ b/lib/ray.rb
@@ -9,4 +9,14 @@ class Ray
   def at(time)
     @origin + (@direction * time)
   end
+
+  def colour(world)
+    if rec = world.hit(self, Interval.new(0, Float::INFINITY))
+      return (Colour.new(1,1,1) + rec.normal) * 0.5
+    end
+
+    unit_dir = 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
 end
diff --git a/lib/vec3.rb b/lib/vec3.rb
index 6287813..b9a5a73 100644
--- a/lib/vec3.rb
+++ b/lib/vec3.rb
@@ -69,6 +69,11 @@ class Colour < Vec3
   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]
+    intensity = Interval.new(0.0, 0.999)
+    "%3d %3d %3d" % [
+      (intensity.clamp(r) * 256).to_i,
+      (intensity.clamp(g) * 256).to_i,
+      (intensity.clamp(b) * 256).to_i
+    ]
   end
 end