From Stephan Huber and Robert Osfield,

Stephan: "attached you'll find some modifications to the GraphicsWindow-class and
their platform-dependant implementations.

The problem:
setWindowRectangle and setWindowDecoration do not update the
traits-object, so, if you call setWindowRectangle on a
not-realized-window it will open with another size when realized later.
getWindowRectangle reports possible wrong sizes if setWindowRectangle
called before.

My solution:
split the implementation in two parts:
GraphicsWindow::setWindowRectangle will update its traits-object and
call afterwards the virtual method setWindowRectangleImplementation
(which is implemented by the derived platformspecific classess). For
setWindowDecoration I am useing a similar mechanism.

I hope you'll find the submission useful, the Win32 and X11 changes are
not tested but should work."

Changes to this made by Robert are call of resized in setWindowRectangle 
instead of setting of Traits, and use of a bool return type.

src/osgViewer/GraphicsWindowWin32.cpp

@@ -1512,7 +1512,7 @@ bool GraphicsWindowWin32::setPixelFormat()
     return true;
 }
 
-void GraphicsWindowWin32::setWindowDecoration( bool decorated )
+bool GraphicsWindowWin32::setWindowDecorationImplementation( bool decorated )
 {
     unsigned int windowStyle;
     unsigned int extendedStyle;
@@ -1527,7 +1527,7 @@ void GraphicsWindowWin32::setWindowDecoration( bool decorated )
     if (!determineWindowPositionAndStyle(decorated, x, y, w, h, windowStyle, extendedStyle))
     {
         reportErrorForScreen("GraphicsWindowWin32::setWindowDecoration() - Unable to determine the window position and style", _traits->screenNum, 0);
-        return;
+        return false;
     }
 
     //
@@ -1540,7 +1540,7 @@ void GraphicsWindowWin32::setWindowDecoration( bool decorated )
     if (result==0 && error)
     {
         reportErrorForScreen("GraphicsWindowWin32::setWindowDecoration() - Unable to set window style", _traits->screenNum, error);
-        return;
+        return false;
     }
 
     //
@@ -1553,7 +1553,7 @@ void GraphicsWindowWin32::setWindowDecoration( bool decorated )
     if (result==0 && error)
     {
         reportErrorForScreen("GraphicsWindowWin32::setWindowDecoration() - Unable to set window extented style", _traits->screenNum, error);
-        return;
+        return false;
     }
 
     //
@@ -1563,7 +1563,7 @@ void GraphicsWindowWin32::setWindowDecoration( bool decorated )
     if (!::SetWindowPos(_hwnd, HWND_TOP, x, y, w, h, SWP_FRAMECHANGED | SWP_NOZORDER | SWP_SHOWWINDOW))
     {
         reportErrorForScreen("GraphicsWindowWin32::setWindowDecoration() - Unable to set new window position and size", _traits->screenNum, ::GetLastError());
-        return;
+        return false;
     }
 
     //
@@ -1574,6 +1574,8 @@ void GraphicsWindowWin32::setWindowDecoration( bool decorated )
     {
         ::InvalidateRect(NULL, NULL, TRUE);
     }
+    
+    return true;
 }
 
 bool GraphicsWindowWin32::realizeImplementation()
@@ -1760,12 +1762,14 @@ void GraphicsWindowWin32::requestWarpPointer( float x, float y )
     getEventQueue()->mouseWarped(x,y);
 }
 
-void GraphicsWindowWin32::setWindowRectangle(int x, int y, int width, int height)
+bool GraphicsWindowWin32::setWindowRectangleImplementation(int x, int y, int width, int height)
 {
     if (!::SetWindowPos(_hwnd, HWND_TOP, x, y, width, height, SWP_SHOWWINDOW | SWP_FRAMECHANGED))
     {
         reportErrorForScreen("GraphicsWindowWin32::setWindowRectangle() - Unable to set new window position and size", _traits->screenNum, ::GetLastError());
+        return false;
     }
+    return true;
 }
 
 void GraphicsWindowWin32::useCursor( bool cursorOn )
@@ -2255,3 +2259,10 @@ struct RegisterWindowingSystemInterfaceProxy
 static RegisterWindowingSystemInterfaceProxy createWindowingSystemInterfaceProxy;
 
 }; // namespace OsgViewer
+
+
+// declare C entry point for static compilation.
+extern "C" void graphicswindow_Win32(void)
+{
+    osg::GraphicsContext::setWindowingSystemInterface(osgViewer::Win32WindowingSystem::getInterface());
+}