Reloading textures after an alt-tab

Okies I've got my renderer cache setup to reload everything (everything being only textures right now) whenever the window gains focus from having lost it (i.e. this doesn't happen when the window is first created).

Do I need to do this every time, or just when I've lost a texture? If only when I've lost one, how do I tell?

I'm using SDL/OpenGL.

You'll always lose the textures (and shaders, and VBOs) after an alt-tab, so you do pretty much need to reload them each time you regain focus (or in any situation where the GL context is reset for that matter).

Okies, thanks for replying :)