* Handle large (delta > 1) movements into the DZ
which are not due to invalid-drop positions, but
caused by laggy GUI or rapid user movements.
* ignore busses when moving out of the DZ.
Allow to drag multiple regions from different tracks
to/from the dropzone.
Busses & Automation-lanes are ignored, as are
hidden tracks.
Any region may serve as mouse drag anchor.
fixes#6172 and #6176
Fixes bug #6214.
It would be better to do this while dragging, but this would require rewriting
much of the drag code to keep track of a cumulative y delta since the current
position of points would be "sticky" and prevent any movement at all, so this
will have to do for now.
Fixes bug #6166 (except record).
This attempts to follow the "current" control value somewhat aggressively:
* On locate, slider is set to the value from the top region at the new
transport position.
* Playback or MIDI input is followed "live".
* Whenever the slider is moved (including automatically), that value is emitted
as an immediate event to keep external gear in sync.
General idea is that the Ardour slider should act as a mirror of an external
hardware knob, and both should be synced to whatever the control is at the
current transport position. Since we lack real playback/touch/etc modes for
these for now, we must choose one behaviour, and this seems like the most
reasonable one.
Follow is handled in the audio thread, which is probably not ideal, but since
these controls have no lists and do not record, should be fine. Probably.
Fixes#6172 and #6176 for single region drags.
Further work is needed if multiple regions on different tracks are dragged over hidden tracks
(see inline comment).
