Fix handling of tall menu windows with the KDE Wayland compositor

Unfortunately (sigh), the KDE Wayland compositor does not seem to support
correctly, that is, as described by the Wayland protocol, popup windows
that are taller than the display : there is no means to make it draw such popup
so that part of it is above the screen top, whereas the 3 other tested compositors
(Mutter, Weston, Sway) don't have this problem.

This commit implements a new approach to draw tall menu windows, and uses
it only with the KDE compositor : instead of asking the compositor to slide the
menu window up, the menu window remains at a fixed position and the graphics
inside the window is slided up.

This requires to add a member variable, int offset_y, to class menuwindow, that
gets used only for the Wayland platform and that contains the vertical offset by which
graphics to the menu window is moved, expressed in FLTK units. An accessor
to the address of this member variable is added to class Fl_Window_Driver.

0 files changed, 0 insertions, 0 deletions