#### control policy at edge of FILL ####
-------------------------------------------
toggle variable (left-click):
  $erodingfillflag -- toggle erode vs. standard
-------------------------------------------
toggle variable (middle-click):
  $dilatingfillflag -- toggle dilate vs. standard
-------------------------------------------


The "er" (erode) tickbox (next to "AREA" button)
controls the operation of "FILL".  By default,
this is unticked -- that is, clicking FILL does
standard fill (neither erode nor dilate).

There are 3 possible states of this tickbox via
left and middle clicks:

  1) unticked, label is "er" => standard FILL
  2) ticked, label is "er" => eroding FILL
  3) unticked, label is "dl" => dilating FILL

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Left-click (toggle $erodingfillflag)
-------------------------------------------

If $erodingfillflag is 1 ("er" is ticked), FILL
will only save vertices *inside* the border of a
cut (i.e., it will discard border vertices).
Thus, each repeated application of FILL
successively erodes one layer of vertices from a
patch.

This can be used to gradually shrink a patch.

This can also be used to construct completely
non-overlapping adjoining labels:

 (1) left-click "er"
 (2) display existing label (FILL will respect it)
 (3) "U"-shaped cut w/both ends in displayed label
 (4) left-click inside cut
 (5) FILL to create non-overlapping label

If "er" is unclicked (the default at startup), by
contrast, the two adjoining labels created by this
process will share vertices at their boundary
(this may be desired).

N.B.: this flag is *always* set to 1 when the ROI
button is used since the ROI operation strictly
uses vertexwise data.

See help for ROI for exact details on how flood
filling is implemented (esp. distinction between
vertices and faces during FILL).

-------------------------------------------
Middle-click (toggle $dilatingfillflag)
-------------------------------------------

If the "er" is middle-clicked (vs. left-clicked)
then $dilatingfillflag will be set to 1 (the "er"
tick label will change to a bold "dl"), and FILL
will add a rim of single vertices around the
fill.  The tickbox will remain unticked.

Repeated applications of FILL with this flag set
will thus successively dilate a patch, one layer
of vertices at a time.

The dilation operation respects any label that
has been displayed with "D", even though the
label might be on part of the surface that has
already been cut away (use CLR on the "label:"
line to clear all displayed labels if this
behavior is not desired).

N.B.: a middle-click will only change to dilating
FILL if the eroding fill tickbox is first
unticked.  Also, if dilating FILL is set (label
is bold "dl") ticking the unticked tickbox will
cancel dilating FILL it and change to eroding
FILL.
