This involved a significant change in event handling for automation region views,
but it brings it into line with how it works for other things. On button press
we initiate a drag, then if no motion occurs, the Drag returns false during
finalization, and only then do we continue through Editor::button_release_handler()
to eventually end up in ::add_automation_event().
Although it is a substantial change, the fact that it now works the same
way for audio regions, automation regions and automation tracks seems
like a definite plus.
Drag::_raw_grab_time is set to the correct time-domain. However
during ::motion() and other operations the adjusted time was
always AudioTime.
Most notably this caused editor->selection->time to have
different time-domains for start and end.
I/O plugin Controls are destroyed with ~IOPlug, however
Session::destroy()'s call to drop_references() still
triggers AutomationControl::session_going_away() on the
binding proxy.
This is even properly documented in session_object.h:
> A named object associated with a Session. Objects derived
> from this class are expected to be destroyed before the
> session calls drop_references().
This reverts commit c578695a64.
When hovering over a control point there is still the "Fader"
cursor shown. It is also handy to be able to directly modify
a control-point right after adding it.
A freehand draw operation can be still be initiated above,
below, or left/right of a given control point.
Playlist::add_region, Playlist::add_region_internal always
adds the region to the top of the playlist, ignoring the
region's layer.
Note that there is also difference between
Region::layer and Region::layering_index.
Previously creating a new preset first attempted to load
it from disk, before creating it. This resulted in a
`XML error: failed to load external entity`.
