Call HitTest in just one place
Can now preserve repeatedly hit UIHandle objects during pre-click motion
Fields of HitTestResult besides the handle pointer are now unused
The need to repaint a track during mouse movement can be indicated when
constructing a UIHandle or when updating it for move; HitPreview no longer
does this
And the last allows simplifications of LabelTrack glyph highlighting
Also move the temporary state for label glyph dragging out of LabelTrack
... Rather, construct them during hit tests (also capturing more state sooner
rather than at Click time, and adding some accessors for later use)
This also fixes bug 1677 by other means and avoids similar problems.
A cell may be implemented to re-use a previously hit handle object, not yet
clicked, in a later hit test, by remembering a weak pointer, but TrackPanel
holds the strong pointers that determine when the object is destroyed.
And the objects will surely be destroyed after drag-release, or ESC key.
For now they are also destroyed whenever not dragging, and hit-testing is
re-invoked; that will be changed later, so that the re-use mentioned above
becomes effective, but still they will be destroyed when the pointer moves
from one cell to another.
... except TrackSelectHandle. Cursor changes to a hand only after button-down.
HitTests give a UIHandle, whenever they also give any cursor or status, even
when it's unsafe to click and drag; Click override is reponsible for cancelling.
SelectHandle::Preview introduces much duplication, but the original in the hit
test will later be deleted.
... Let cell hit tests, and handle preview, know states only, not transitions.
Cell hit tests are passed a mouse state that does not always match the current,
but anticipates the button click to come; usually left, but if the Control
[sic] key on Mac is down, then right.
Thus, pressing and releasing Mac Control in multi-tool switches in and out of
the magnifier cursor.
If you hover exactly above the split line, you now get a pointing hand icon and status message, allowing you to start a selection at the split line more easily.
This allows selection and clicking on split lines to merge clips to act independently. It also means we don't need a portmanteau explanation in the status line, and the action to select up to a split line is simpler and easier to explain.
... those handles that force a simulated button-up when play interrupts drag,
and can assume that pointers to tracks remain nonNULL and part of the current
project state (not the undo history).
Also pass shared_ptr to Track into more hit test routines.
Zoom tool takes precedence;
Otherwise do special hits appropriate to the track subclass -- and only
WaveTrack here uses Tools toolbar state, and now disallows clicks on things
when they are not drawn because the view is spectrogram;
Finally, default to right button zooming in Multi tool, or to time shift in
that tool, or to selection adjustment in Multi or in Select tool.
