Add Gui class and move GUI logic from main module to it.

src/jes/gui/package.d

@@ -0,0 +1,63 @@
+module jes.gui;
+
+static import jtk;
+import derelict.opengl;
+import std.stdio;
+
+class Gui
+{
+    jtk.Window[] m_windows;
+
+    this()
+    {
+        if (!jtk.init())
+        {
+            throw new Exception("JTK initialization failed.");
+        }
+    }
+
+    void run()
+    {
+        try
+        {
+            m_windows ~= new jtk.Window();
+            event_loop();
+            m_windows[0].close();
+        }
+        finally
+        {
+            jtk.quit();
+        }
+    }
+
+    private void event_loop()
+    {
+        bool running = true;
+        while (running)
+        {
+            jtk.Event event = jtk.wait_event();
+            switch (event.type)
+            {
+            case jtk.Event.WINDOW_CLOSE:
+                running = false;
+                break;
+
+            case jtk.Event.WINDOW_RESIZE:
+                glViewport(0, 0, event.window_resize.width, event.window_resize.height);
+                redraw_window(event.window_resize.window);
+                break;
+
+            default:
+                break;
+            }
+        }
+    }
+
+    private void redraw_window(jtk.Window window)
+    {
+        glClearColor(0.5, 0.0, 1.0, 0.0);
+        glClear(GL_COLOR_BUFFER_BIT);
+        m_windows[0].swap_buffers();
+    }
+
+}

src/main.d

@@ -1,50 +1,15 @@
-static import jtk;
 import std.stdio;
-import derelict.opengl;
-
-jtk.Window window;
-
-static void redraw()
-{
-    glClearColor(0.5, 0.0, 1.0, 0.0);
-    glClear(GL_COLOR_BUFFER_BIT);
-    window.swap_buffers();
-}
+import jes.gui;
 
 int main(string[] args)
 {
-    if (!jtk.init())
+    version(unittest)
     {
-        stderr.writeln("JTK initialization failed.");
-        return 1;
     }
-    try
+    else
     {
-        window = new jtk.Window();
-        bool running = true;
-        while (running)
-        {
-            jtk.Event event = jtk.wait_event();
-            switch (event.type)
-            {
-            case jtk.Event.WINDOW_CLOSE:
-                running = false;
-                break;
-
-            case jtk.Event.WINDOW_RESIZE:
-                glViewport(0, 0, event.window_resize.width, event.window_resize.height);
-                redraw();
-                break;
-
-            default:
-                break;
-            }
-        }
-        window.close();
-    }
-    finally
-    {
-        jtk.quit();
+        Gui g = new Gui();
+        g.run();
     }
     return 0;
 }