We currently only ensure that width and height are positive, so it
is still possible to pass in values that don't make any sense at all
(which may even result in a crash when exceeding limits imposed by
X11).
There is nothing to screenshot outside the actual screen area, so
restrict the parameters to that.
https://bugzilla.gnome.org/show_bug.cgi?id=699752
The "flash" effect looks awkward when it fades in and out. Real
camera have an immediate flash of light, which then seems to fade
out as our eyes readjust the rapid change in lighting.
https://bugzilla.gnome.org/show_bug.cgi?id=691875
Since we're breaking API already, take this as an occasion to use a
separate interface for all the screenshot-related methods. The interface
name is org.gnome.Shell.Screenshot.
Internally, move all the related code to screenshot.js.
https://bugzilla.gnome.org/show_bug.cgi?id=688004
