This fixes an issue on Windows, where UI::run can dispatch
a signal that ends up via cross-thread channel at the surfaces'
BaseUI::request_handler. causing a segfault.
First see 31c6f66d9b and 5cb6e1046b.
It worked previously due to `AutomationControl::get_value`
evaluating automation, which was removed in 5cb6e1046b
in favor of properly using latency compensated evaluation.
However due to 31c6f66d9b, fader and trim automation were
never evaluated on locate, only during playback via
`Amp::setup_gain_automation`.
This fixes a case where gain is incorrect after a locate.
The amp still has the gain from before the locate, and when starting
playback ramps to the new gain.
`set_input/output_channels` API to limit a device to the first
`N` chnanels is somewhat ill conveived and was never really
used or useful. LiveTrax has a bitset of exposed channels,
which makes a lot more sense (e.g. hide ADAT or S/Pdif, or
some specific channels)
The MIDI specification makes it quite clear that when a receiver
receives the MSB of a 14 bit controller value, it should consider
the LSB reset to zero. This has been an error in Ardour for many,
many years, though likely of little consequence
This removes the _io_lock in favor of a RCU.
The reason for this change is to ensure data structure
consistency, notably iterators. Previously adding/removing
ports invalidated iterators, which caused [rare] crashes,
since IO::ports() simply returned a PortSet reference.
(This breaks API)
Previously the group-tab extended all the way down to the
last track. Potentially with a widget height of > 2^15 px.
This caused issues with gtk widgets (notably on Windows)
```
unhandled exception (type std::exception) in signal handler:
what: invalid value (typically too big) for the size of the input (surface, pattern, etc.)
```
This also prepares for Mixer Tab-Group to use the same
separation between visible and total extent.
When double-clicking to edit a fader value three button press
events are created:
1. GDK_BUTTON_PRESS
2. GDK_BUTTON_PRESS
3. GDK_2BUTTON_PRESS
The first two start an Editor Drag, which later crashes in
Editor::mid_track_drag() gtk2_ardour/editor.cc:7067
