[vtkusers] Need to change some of vtkImageTracerWidget -- pointers?

[kent williams]

Here's what I want to write: A manual tracing program using
vtkImageTracerWidget.  Use case:

1. Load a brain volume
2. For each relevant slice of the volume
     trace the feature in that slice
3. Use the collection of resulting polygons or polylines, generate a
3D binary image, based on all traces.

Some behaviors I'd like to have:

1. When tracing is turned off in the view, still display the traced
outline, but not allow modification of the outline.

2. When the user selects a new slice, the traced outline associated
with that slice will be displayed and any other outlines are not.

3. Get rid of the default left mouse button behaviro during tracing
which is to restart the trace with one point.  Given that clicking the
first mouse button is the most common mouse event, it feels like it's
too easy to lose your work!

So here's where I'm confused -- would I have one tracer widget and use
it for all slices, but save out the polyline data when I change
slices, or would I have multiple tracer widgets, one per slice, and
enable and disable them when the slice changes?

Thanks!