1 files changed, 137 insertions, 0 deletions
diff --git a/lib/irb/easter-egg.rb b/lib/irb/easter-egg.rb
new file mode 100644
index 0000000000..64869d85fa
--- /dev/null
+++ b/lib/irb/easter-egg.rb
@@ -0,0 +1,137 @@
+require "reline"
+
+module IRB
+  class << self
+    class Vec
+      def initialize(x, y, z)
+        @x, @y, @z = x, y, z
+      end
+
+      attr_reader :x, :y, :z
+
+      def sub(other)
+        Vec.new(@x - other.x, @y - other.y, @z - other.z)
+      end
+
+      def dot(other)
+        @x*other.x + @y*other.y + @z*other.z
+      end
+
+      def cross(other)
+        ox, oy, oz = other.x, other.y, other.z
+        Vec.new(@y*oz-@z*oy, @z*ox-@x*oz, @x*oy-@y*ox)
+      end
+
+      def normalize
+        r = Math.sqrt(self.dot(self))
+        Vec.new(@x / r, @y / r, @z / r)
+      end
+    end
+
+    class Canvas
+      def initialize((h, w))
+        @data = (0..h-2).map { [0] * w }
+        @scale = [w / 2.0, h-2].min
+        @center = Complex(w / 2, h-2)
+      end
+
+      def line((x1, y1), (x2, y2))
+        p1 = Complex(x1, y1) / 2 * @scale + @center
+        p2 = Complex(x2, y2) / 2 * @scale + @center
+        line0(p1, p2)
+      end
+
+      private def line0(p1, p2)
+        mid = (p1 + p2) / 2
+        if (p1 - p2).abs < 1
+          x, y = mid.rect
+          @data[y / 2][x] |= (y % 2 > 1 ? 2 : 1)
+        else
+          line0(p1, mid)
+          line0(p2, mid)
+        end
+      end
+
+      def draw
+        @data.each {|row| row.fill(0) }
+        yield
+        @data.map {|row| row.map {|n| " ',;"[n] }.join }.join("\n")
+      end
+    end
+
+    class RubyModel
+      def initialize
+        @faces = init_ruby_model
+      end
+
+      def init_ruby_model
+        cap_vertices    = (0..5).map {|i| Vec.new(*Complex.polar(1,  i        * Math::PI / 3).rect, 1) }
+        middle_vertices = (0..5).map {|i| Vec.new(*Complex.polar(2, (i + 0.5) * Math::PI / 3).rect, 0) }
+        bottom_vertex   = Vec.new(0, 0, -2)
+
+        faces = [cap_vertices]
+        6.times do |j|
+          i = j-1
+          faces << [cap_vertices[i], middle_vertices[i], cap_vertices[j]]
+          faces << [cap_vertices[j], middle_vertices[i], middle_vertices[j]]
+          faces << [middle_vertices[i], bottom_vertex, middle_vertices[j]]
+        end
+
+        faces
+      end
+
+      def render_frame(i)
+        angle = i / 10.0
+        dir = Vec.new(*Complex.polar(1, angle).rect, Math.sin(angle)).normalize
+        dir2 = Vec.new(*Complex.polar(1, angle - Math::PI/2).rect, 0)
+        up = dir.cross(dir2)
+        nm = dir.cross(up)
+        @faces.each do |vertices|
+          v0, v1, v2, = vertices
+          if v1.sub(v0).cross(v2.sub(v0)).dot(dir) > 0
+            points = vertices.map {|p| [nm.dot(p), up.dot(p)] }
+            (points + [points[0]]).each_cons(2) do |p1, p2|
+              yield p1, p2
+            end
+          end
+        end
+      end
+    end
+
+    private def easter_egg(type = nil)
+      type ||= [:logo, :dancing].sample
+      case type
+      when :logo
+        File.open(File.join(__dir__, 'ruby_logo.aa')) do |f|
+          require "rdoc"
+          RDoc::RI::Driver.new.page do |io|
+            IO.copy_stream(f, io)
+          end
+        end
+      when :dancing
+        begin
+          canvas = Canvas.new(Reline.get_screen_size)
+          Reline::IOGate.set_winch_handler do
+            canvas = Canvas.new(Reline.get_screen_size)
+          end
+          ruby_model = RubyModel.new
+          print "\e[?1049h"
+          0.step do |i| # TODO (0..).each needs Ruby 2.6 or later
+            buff = canvas.draw do
+              ruby_model.render_frame(i) do |p1, p2|
+                canvas.line(p1, p2)
+              end
+            end
+            buff[0, 20] = "\e[0mPress Ctrl+C to stop\e[31m\e[1m"
+            print "\e[H" + buff
+            sleep 0.05
+          end
+        ensure
+          print "\e[0m\e[?1049l"
+        end
+      end
+    end
+  end
+end
+
+IRB.send(:easter_egg, ARGV[0]&.to_sym) if $0 == __FILE__