The controller has always tracked its selection; nothing drew it, so a Ctrl or
Shift drag framed a range with no feedback until the release.
The preview is the area the release will change, not what the pointer swept:
Ctrl frames the x range only, so a band across the plot is what it will zoom,
where the sliver a straight horizontal drag sweeps is only the gesture. The
plot carries the rect a host hands it -- it learns nothing about pointers --
and the renderer draws a low-alpha fill under a light border over everything
else inside the axes.
Martino Ferrari
be1f31a04f