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Backup behind windows take a copy of the screen they are going to obliterate and blit it back to the screen when they disappear rather than issuing a redraw to the application behind. They may backup the part of the screen obscured by the window or the whole of screen. Backing up the whole screen is useful for windows that require the rest of the screen to fade when they are displayed. such as fading the window behind the dialog with focus.
The function RWindowBase::EnableBackup()
sets a
window to have one of at least two different types of backup,
EWindowBackupAreaBehind
which is just the area behind this window
(the default), and EWindowBackupFullScreen
, which is the whole
screen.
EWindowBackupFullScreen
allows you to have a fade behind
window and when it becomes unfaded behind, the screen will be redrawn by the
window server instead of issuing redraw events to all the apps. The window fade
behind backup flag should be set for a window before the window is activated
and before calling the fade behind
RWindowBase::FadeBehind()
function. If it is called after
activating the window then the backup will not include the part of the screen
obscured by the window itself.