Code review comment for lp:~gerboland/miral/qt-distinguish-visible-exposure

They have different purposes.

Clients set their surface state, and can use those states to inform Mir/Shell if a surface should be visible not. That is what WindowInfo::is_visible decides for us.

But the mir_surface_attrib_visibility is how Mir/Shell tells the client that its surface is occluded or not. Then client can decide to stop drawing useless frames.

They're different concepts, but with similar names, so I separated them and renamed the later to "exposed" to hopefully reduce the confusion.