diff -r -u --strip-trailing-cr ./original/vtkWin32OpenGLRenderWindow.cxx ./patched/vtkWin32OpenGLRenderWindow.cxx
--- ./original/vtkWin32OpenGLRenderWindow.cxx	2013-05-23 18:53:34.352238900 +0400
+++ ./patched/vtkWin32OpenGLRenderWindow.cxx	2013-05-23 15:33:30.221945900 +0400
@@ -538,6 +538,9 @@
                                                   int debug, int bpp, 
                                                   int zbpp)
 {
+  // register "vtkOpenGL" window class
+  RegisterWndClass();
+
   // Create a dummy window, needed for calling wglGetProcAddress.
 #ifdef UNICODE
   HWND tempId = CreateWindow(L"vtkOpenGL", 0, 0, 0, 0, 1, 1, 0, 0, this->ApplicationInstance, 0);
@@ -893,7 +896,6 @@
 
     if (!this->WindowId)
       {
-      WNDCLASS wndClass;
       this->DeviceContext = 0;
 
       int len = static_cast<int>(strlen("Visualization Toolkit - Win32OpenGL #"))
@@ -904,32 +906,8 @@
       this->SetWindowName(windowName);
       delete [] windowName;
 
-      // has the class been registered ?
-#ifdef UNICODE
-      if (!GetClassInfo(this->ApplicationInstance,L"vtkOpenGL",&wndClass))
-#else
-        if (!GetClassInfo(this->ApplicationInstance,"vtkOpenGL",&wndClass))
-#endif
-          {
-          wndClass.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
-          wndClass.lpfnWndProc = vtkWin32OpenGLRenderWindow::WndProc;
-          wndClass.cbClsExtra = 0;
-          wndClass.hInstance = this->ApplicationInstance;
-          wndClass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
-          wndClass.hCursor = LoadCursor(NULL, IDC_ARROW);
-          wndClass.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
-          wndClass.lpszMenuName = NULL;
-#ifdef UNICODE
-          wndClass.lpszClassName = L"vtkOpenGL";
-#else
-          wndClass.lpszClassName = "vtkOpenGL";
-#endif
-          // vtk doesn't use the first extra vtkLONG's worth of bytes,
-          // but app writers may want them, so we provide them. VTK
-          // does use the second vtkLONG's worth of bytes of extra space.
-          wndClass.cbWndExtra = 2 * sizeof(vtkLONG);
-          RegisterClass(&wndClass);
-          }
+      // register "vtkOpenGL" window class
+      RegisterWndClass();
 
 #ifdef UNICODE
       wchar_t *wname = new wchar_t [mbstowcs(NULL, this->WindowName, 32000)+1];
@@ -1047,6 +1025,39 @@
     }
 }
 
+// Register window class.
+void vtkWin32OpenGLRenderWindow::RegisterWndClass()
+{
+  WNDCLASS wndClass;
+
+  // has the class been registered ?
+#ifdef UNICODE
+  if (!GetClassInfo(this->ApplicationInstance,L"vtkOpenGL",&wndClass))
+#else
+  if (!GetClassInfo(this->ApplicationInstance,"vtkOpenGL",&wndClass))
+#endif
+    {
+    wndClass.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
+    wndClass.lpfnWndProc = vtkWin32OpenGLRenderWindow::WndProc;
+    wndClass.cbClsExtra = 0;
+    wndClass.hInstance = this->ApplicationInstance;
+    wndClass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
+    wndClass.hCursor = LoadCursor(NULL, IDC_ARROW);
+    wndClass.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
+    wndClass.lpszMenuName = NULL;
+#ifdef UNICODE
+    wndClass.lpszClassName = L"vtkOpenGL";
+#else
+    wndClass.lpszClassName = "vtkOpenGL";
+#endif
+    // vtk doesn't use the first extra vtkLONG's worth of bytes,
+    // but app writers may want them, so we provide them. VTK
+    // does use the second vtkLONG's worth of bytes of extra space.
+    wndClass.cbWndExtra = 2 * sizeof(vtkLONG);
+    RegisterClass(&wndClass);
+    }
+}
+
 // Initialize the window for rendering.
 void vtkWin32OpenGLRenderWindow::WindowInitialize()
 {
diff -r -u --strip-trailing-cr ./original/vtkWin32OpenGLRenderWindow.h ./patched/vtkWin32OpenGLRenderWindow.h
--- ./original/vtkWin32OpenGLRenderWindow.h	2013-05-23 18:53:34.340237700 +0400
+++ ./patched/vtkWin32OpenGLRenderWindow.h	2013-05-23 15:31:58.473772000 +0400
@@ -262,6 +262,7 @@
   void ResizeWhileOffscreen(int xsize, int ysize);
   virtual void CreateAWindow();
   virtual void DestroyWindow();
+  void RegisterWndClass();
   void InitializeApplication();
   void CleanUpOffScreenRendering(void);
   void CreateOffScreenDC(int xsize, int ysize, HDC aHdc);