Replaces the list of points in TempoMap with TempoSection functions, which
compute tempo-at or tick-at time relative to tempo section start.
TempoMap consults them additively to determine things like bbt_time(),
frame_time() get_grid() etc.
This has a marked effect on scrolling speed along with the code simplification
in the places it has been attempted.
Several things are broken here.
Currently every ramp except the last one is an exponential ramp. this may
be simple to fix :).
Mouse-over midi grid doesn't match mouse click grid. should also be simple.
Many things seem to work, but their accuracy should be in question until
each area has been addressed.
uselib is no longer implicit (inherited by .use). This is still incomplete,
some uselibs for non-linux variants may be missing.
bld.is_defined("HAVE_XXX") also no longer works and will have to be
changed (I think to bld.env["HAVE_XXX"]) in countless places.
Backport from Mixbus. In Ardour this does not currently matter
since there is no top-level canvas destroyed top-down.
...
Editor::session_going_away
MixerStrip::~MixerStrip
MixbusStripCanvas::~MixbusStripCanvas
ArdourCanvas::GtkCanvas::~GtkCanvas
ArdourCanvas::Canvas::~Canvas
ArdourCanvas::Root::~Root
ArdourCanvas::Container::~Container
ArdourCanvas::Item::~Item
ArdourCanvas::Item::clear_items
GtkCanvas::item_going_away()
queue_draw_item_area()
..expose can take place async to garbage collection: crash in one of the
items.
There is a highly unlikely case where the render thread can have zero
requests in the queue, but it is not supposed to be terminated.
1) WaveView::queue_get_image();
wake up thread, *but* the thread does not start yet
2) WaveView::cancel_my_render_request();
and now the thread starts.
1,2 are initiated by user actions from the GUI thread and are normally
orders of magnitude slower than scheduler-thread wakeup.
