Locking B3D scaled window to certain sizes

Is there a way in which I can create my game in a scaled window mode, i.e Graphics3D 320,240,0,3 and then only allow the user to resize the created window to certain multiples of this number? x2, x3 etc...

So the user could for example drag the window to the next size up which would be 640x480 and then again up to 1280x960 but nothing in between.

Any help would be greatly appreciated along with a possible example :)

Jason.

I may be wrong but I doubt it very much, TBH.

I'm also unsure why you'd want/need this functionality.

I have my reasons.... Any ideas anyone as to how this could be achieved?

I partly need this technique as I need my graphics to survive a window size change and if I manually set another windowed mode in code then I get an error as I seem to remember that you need to load your images after calling the graphics command. I do not want to restart my game just to change this window size basically which is why I`m seeking a different approach.

I also need my graphics to maintain their correct aspect ratio so simply using a scalable window is not good enough, it has to be able to be changed to set sizes\resolutions.

Jason.