... Because all hit tests returned all fields blank, or else, returned a
UIHandle object whose Preview method gives the rest of the information; so
the other fields were redundant.
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.
