OpenGL Viewport On Drag Update (Winapi) - c++

Question

In my current project I am working on I would like to make the opengl viewport window resize from when the user resizes the drag window ("SizeBox"), I planned on using the windows "ENTERSIZEMOVE" function from the windows.h window api to get the signal to redraw the viewport.I would then call "UpdateRender" to update my viewport.
On running my program I only seem to get one update call to resize the window (even if I stop and start dragging again),I also have a cube in the scene which is rotating it is entered (0.0f,0.0f,10.of). I wanted the cube to move along with the window "resizing" instead of it getting covered over by the window,Since the cube is set to the centre of the viewport so if I am correct I should not need to move it via a gltransform.
If anyone has any thoughts on why I am not getting a constant viewport "refresh" from the window being dragged it would be much appreciated.
Message loop handler (snippet)
{ case WM_ENTERSIZEMOVE:
render->UpdateRender();
break;
}
Update Render
void Render::UpdateRender()
{
int update_x = rect.right - rect.left;
int update_y = rect.bottom - rect.top;
glViewport(0,0 ,update_y/2,update_x/2);
}
Create Window
int window::Wincreate(HINSTANCE hInstance, char *winname, int winwidth, int winheight)
{
Hwnd = CreateWindow("Game Engine", winname, WS_VISIBLE | WS_SYSMENU | WS_SIZEBOX | WS_MAXIMIZEBOX | WS_MAXIMIZE, 0, 0, winwidth , winheight , 0, 0, hInstance, 0);
if (!Hwnd)
{
MessageBox(0, "Error: Could not Create Window", "Error", MB_OK);
}
Engine->EnableOGLAPI();
Draw->Initalize();
return 0;
}
Main application Loop
int window::Winloop(MSG msg)
{
while (running)
{
if (PeekMessage(&msg,0,0,0,PM_REMOVE))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
else
{
angle++;
Draw->MainRender();
SwapBuffers(hDC);
}
}
return 0;
}