Mixbus in particular uses both types of tooltip so we might as well make them look the same.
N.B. The appearance is fine now on Windows but needs to be tested on the other platforms (i.e. some tweaking might be necessary).
All canvas objects share just one tooltip object which is based around Gtk::Label. The Label expands if the current tooltip text is wider than the previous text. However, it doesn't shrink again if the next tooltip has shorter text. Eventually, this results in some very strange looking tooltips (especially in Mixbus where they're used quite extensively).
Deleting the object after use will force a new object to get generated next time (at the correct size). There's still only ever one object per canvas but it's no longer persistent.
Technically it doesn't make much difference but from what I can tell, the only files which #include 'gtk2_ardour/gui_thread.h' are the source files from gtk2_ardour itself. The support libraries always #include 'gtkmm2ext/gui_thread.h' directly (which seems sensible). So for consistency's sake, let's keep it the same for libcanvas.
Invalidate all source entries from the image cache when we get our
region's DropReferences signal, while ignoring any subsequent regions with
no source.
Fixes bug #6179. Top vs. bottom seems pretty arbitrary to me, and this solves
the obscuring issue (which is quite common since there are often PC events at
the start of MIDI files), so bottom it is.
In summary:
* no antialiasing of waveviews
* no diagonal lines
* simplify clip detection
* don't use LINE_CAP_ROUND for outline
* use the wave colour when drawing outline only
Gtk coalesces multiple exposes into a single combined rect.
If _single_exposure is disabled, we break apart the individual expose rects for the canvas rendering.
The region is the un-coalesced set of rectangles that were requested for redraw. The area
is the coalesced single rectangle. In the worst cases, the coalesced rectangle could span
the entire window even though just two pixels in opposite corners were to be redrawn.
There is a problem with the verbose cursor as it is dragged across MIDI tracks. TO BE
FIXED.
The problem this is avoiding makes absolutely no sense. Either I'm dumb, or
something is more deeply wrong with scroll group bounding boxes, or both, but I
don't care anymore. This works. Viva release mode.
