Once upon a time, there was a function called gdk_event_get_scroll_deltas().
It returned %TRUE when an event had scroll deltas and that was used as the
condition to decide whether to push scroll deltas to the scroll history,
even when the both deltas are 0 for the stop event at the end of scrolling.
When GtkScrolledWindow kinetic scrolling code was adapted for
GtkEventControllerScroll, it was replaced with a (dx != 0 && dy != 0)
check. This prevented the stop event from getting into the history, and
instead allowed non-smooth scrolling to affect the history as they have
synthetic deltas with one of the values being -1 or 1 and the other on 0.
Instead, check the direction as we already have it as a local variable.
We don't need to cover every case with a va_marshaller, but there are a
number of them that are useful because they will often only be connected
to by a single signal handler.
Generally speaking, if I opened into a file to add a va_marshaller, I just
set all of them.
If we set c_marshaller manually, then g_signal_newv() will not setup a
va_marshaller for us. However, if we provide c_marshaller as NULL, it will
setup both the c_marshaller (to g_cclosure_marshal_VOID__VOID) and
va_marshaller (to g_cclosure_marshal_VOID__VOIDv) for us.
There is a gtk_event_controller_scroll_set_flags() call that's meant
to be called after construction (eg. due to scrolledwindow relayouts
hiding/showing scrollbars). The property shouldn't be construct-only
for consistence.
This is a GtkEventController implementation to handle mouse
scrolling. It handles both smooth and discrete events and
offers a way for callers to tell their preference too, so
smooth events shall be accumulated and coalesced on request.
On capable devices, it can also emit ::scroll-begin and
::scroll-end enclosing all ::scroll events for a scroll
operation.
It also has builtin kinetic scrolling capabilities, reporting
the initial velocity for both axes after ::scroll-end if
requested.
