When I create a large canvas, set it to virtual mode, and use the scroll bars to move around it, how do I receive events (like %WM_HSCROLL) for those scroll bars? I'd like to update other controls in my main window as the user drags the canvas around under the viewport.

I have set my canvas up to use a callback, and in that callback I'm looking for %WM_HSCROLL and %WM_VSCROLL but I never see them come through.