EventControllerScroll is an event controller meant to handle scroll events from mice and touchpads.
It is capable of handling both discrete and continuous scroll events, abstracting them both on the
scroll signal (deltas in the discrete case are multiples of 1).
In the case of continuous scroll events, EventControllerScroll encloses all
scroll events between two
scroll_begin and
scroll_end signals.
The behavior of the event controller can be modified by the flags given at creation time, or modified at a later point through
set_flags (e.g. because the scrolling conditions of the widget
changed).
The controller can be set up to emit motion for either/both vertical and horizontal scroll events through
VERTICAL,
HORIZONTAL and GTK_EVENT_CONTROLLER_SCROLL_BOTH
. If any axis is disabled, the respective scroll delta will be
0. Vertical scroll events will be translated to horizontal motion for the devices incapable of horizontal scrolling.
The event controller can also be forced to emit discrete events on all devices through
DISCRETE. This can be used to implement discrete actions
triggered through scroll events (e.g. switching across combobox options).
The KINETIC flag toggles the emission of the
decelerate signal, emitted at the end of scrolling with two X/Y
velocity arguments that are consistent with the motion that was received.