diff --git a/runtime/lib/window.rb b/runtime/lib/window.rb
index 6cf382c..c5f2a3c 100644
--- a/runtime/lib/window.rb
+++ b/runtime/lib/window.rb
@@ -1,7 +1,26 @@
+require "set"
+
 class Window
+  @windows = Set.new
+
+  class << self
+    def register(window)
+      @windows << window
+    end
+
+    def remove(window)
+      @windows.delete(window)
+    end
+  end
+
   def initialize
     @programs = {}
     load_shaders
+    Window.register(self)
+  end
+
+  def close
+    Window.remove(self)
   end
 
   private
diff --git a/src/GUI.cc b/src/GUI.cc
index f17b04a..5249b11 100644
--- a/src/GUI.cc
+++ b/src/GUI.cc
@@ -1,8 +1,4 @@
 #if 0
-#include "GUI.h"
-#include "gl3w.h"
-#include <iostream>
-
 bool GUI::load()
 {
     glClearColor (0.0, 0.0, 0.0, 0.0);
@@ -40,39 +36,6 @@ bool GUI::load_buffers()
     return true;
 }
 
-int GUI::run()
-{
-    resize();
-    draw();
-
-    SDL_Event event;
-    while (SDL_WaitEvent(&event))
-    {
-        if (event.type == SDL_QUIT)
-            break;
-        else if (event.type == SDL_KEYDOWN)
-        {
-            if (event.key.keysym.sym == SDLK_ESCAPE)
-                break;
-        }
-        else if (event.type == SDL_WINDOWEVENT)
-        {
-            switch (event.window.event)
-            {
-            case SDL_WINDOWEVENT_EXPOSED:
-                draw();
-                break;
-            case SDL_WINDOWEVENT_RESIZED:
-                resize();
-                draw();
-                break;
-            }
-        }
-    }
-
-    return 0;
-}
-
 void GUI::resize()
 {
     GLint viewport_size[2];
diff --git a/src/Window.cc b/src/Window.cc
index bbedd06..26b3396 100644
--- a/src/Window.cc
+++ b/src/Window.cc
@@ -97,8 +97,40 @@ static VALUE Window_new(VALUE klass)
     return rv;
 }
 
+static VALUE Window_event_loop(VALUE klass)
+{
+    SDL_Event event;
+
+    while (SDL_WaitEvent(&event))
+    {
+        if (event.type == SDL_QUIT)
+            break;
+        else if (event.type == SDL_KEYDOWN)
+        {
+            if (event.key.keysym.sym == SDLK_ESCAPE)
+                break;
+        }
+        else if (event.type == SDL_WINDOWEVENT)
+        {
+            switch (event.window.event)
+            {
+            case SDL_WINDOWEVENT_EXPOSED:
+//                draw();
+                break;
+            case SDL_WINDOWEVENT_RESIZED:
+//                resize();
+//                draw();
+                break;
+            }
+        }
+    }
+
+    return Qnil;
+}
+
 void Window_Init(void)
 {
     ruby_class = rb_define_class("Window", rb_cObject);
     rb_define_singleton_method(ruby_class, "new", (VALUE(*)(...))Window_new, 0);
+    rb_define_singleton_method(ruby_class, "event_loop", (VALUE(*)(...))Window_event_loop, 0);
 }