The plug-in dialog GUI was always visible in my full-screen screenshots
on KDE, when no delay. It seems the culprit is their fading out effect
which takes longer than the screenshot to happen, therefore the dialog
was showing up with transparency.
... and a delay before the screenshot.
Until now, there was only delay before selection, which I changed in
commits d9cd4b61bc and 614bcf6d0a. Actually a delay before selection may
also be useful, for instance when you use a tablet without keyboard (no
alt-tab possible) and the window/area you wish to capture is behind GIMP
window. Then you'd want to interact with the desktop with the pointer
before the cursor changes for selection interaction.
I add some logics so that the selection delay doesn't show when it is
unecessary (for instance for full-screen screenshot, or when the window
screenshot is based on the active window, not click selection, like with
GNOME shell API).
Only thing I could not properly figure out yet is how to select an area.
The "screenshotArea" method is there in KDE API, but it needs
coordinates and I can't find the API to grab coordinates in Wayland (as
in GNOME shell API).
