diff --git a/2019/ruby/day_11.rb b/2019/ruby/day_11.rb
new file mode 100644
index 0000000..be15da5
--- /dev/null
+++ b/2019/ruby/day_11.rb
@@ -0,0 +1,55 @@
+require "stringio"
+
+require_relative "computer"
+
+panels = Hash.new {|h,k| h[k] = [0]}
+panels[[0, 0]] = [1]
+
+i_r, i_w = IO.pipe
+o_r, o_w = IO.pipe
+
+Robot = Struct.new(:panel, :dir)
+
+dirs = %i[ up right down left ]
+robot = Robot.new([0, 0], 0)
+
+t = Thread.new {
+  loop do
+    i_w.puts(panels[robot.panel].last)
+
+    panels[robot.panel] << o_r.gets.to_i
+    dir = o_r.gets.to_i
+
+    delta = case dir
+            when 0 then -1
+            when 1 then 1
+            else raise "unexpected direction: #{dir}"
+            end
+    robot.dir += delta
+    robot.dir %= dirs.size
+    dir = dirs.fetch(robot.dir)
+
+    delta = case dir
+            when :up    then [ 0,  1]
+            when :right then [ 1,  0]
+            when :down  then [ 0, -1]
+            when :left  then [-1,  0]
+            end
+    robot.panel = robot.panel.zip(delta).map {|a,b| a + b }
+  end
+}
+
+Thread.new { Computer.from(ARGF.read).run(i_r, o_w) }.join
+
+# p panels.values.count {|v| v.size > 1 }
+
+min_x, max_x = panels.keys.map(&:first).minmax
+min_y, max_y = panels.keys.map(&:last).minmax
+
+letters = (min_y..max_y).map {|y|
+  (min_x..max_x).map {|x|
+    (panels[[x, y]].last == 1) ? ?█ : " "
+  }.join
+}.reverse.join("\n")
+
+puts letters