DeferWindowPos and SWP_SHOWWINDOW/SWP_HIDEWINDOW

Question

I am writing a virtual desktop application which utilises the DeferWindowPos API functions. The current method I am using is moving the windows off the screen if they're not on the current virtual desktop. However I know wish to also hide the windows that are off-screen so they do not appear on the task bar. I have attempted this by also passing SWP_SHOWWINDOW/SWP_HIDEWINDOW to the DeferWindowPos() calls. I have read a few sites regarding this and one of them suggested that if SWP_SHOWWINDOW/SWP_HIDEWINDOW are passed, then the window will only show or hide, and no reposition. Can anyone confirm this, or am I doing something wrong?

Answer 1

You need to read the documentation, which clearly states

If any of the windows in the multiple-window- position structure have the SWP_HIDEWINDOW or SWP_SHOWWINDOW flag set, none of the windows are repositioned.

Answer 2

In addition to the rtfm, DeferWindowPos is eventually going to call SetWindowPos. SetWindowPos always validates its parameters by passing them to the WindowProc via WM_WINDOWPOSCHANGING so, unless you are also hooking every windows WindowProc as part of your virtual desktop manager, moving them off screen is going to fail for any windows where the devs are doing something "clever" or unusual - like clamping to the edge of the workspace.