### select cursor extensions
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toggle variable (left-click):
  toggles value of $selectdmax: "click closeness" criterion
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toggle variable (middle-click):
  $selectinsideflag -- select inside surf instead, adj lighting
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The "clo" tickbox (lower middle) toggles between
the default permissive click-to-vertex criterion
($selectdmax = 2.0 mm) and a rigorous criterion
($selectdmax = 0.25 mm).

Normally, the first vertex within 2 mm of a
perpendicular line from the screen surface to the
cortical surface is selected.  This makes it hard
to 'miss' a vertex.  However, in special cases
(e.g., a 'deep canyon' in a highly folded
cerebellar surface), this can end up selecting a
vertex on one of the 'canyon walls'.  To decrease
the nearness criterion to 0.25 mm, click the
"clo" button at the bottom middle.  Other
criteria can be set by directly adjusting the
tcl/C variable, $selectdmax.

With "clo" ticked, some clicks may now miss
selecting any vertex, and you will have to click
more accurately.

The (tcl-only) variable of the tickbox is
$selectcloseflag.

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toggle variable (middle-click):
  $selectinsideflag -- select inside surface, adj lighting
-------------------------------------------

An alternate middle-click on the "clo" tickbox
(middle bottom) toggles $selectinsideflag.  When
this flag is ON, vertices can be selected from
the inside/back surface.

N.B.: this will disable the normal selecting of
vertices on the outside of the surface!
(middle=click again to go back to normal).

This rarely-used facility was written to help
with editing extermely convoluted surfaces such
as the anterior lobe vermis of the human
cerebellum.

To make the surface and the selected vertices
visible, two additional variables are adjusted:

  set lighttwosidedflag 1   ;# show inside surface
  set light1 1.0                ;# also light inside/back surface

Selections on the inside surface are also marked
when viewing the surface from the outside.

A shift-R-click on the "REDRAW" button makes a
popup with full control over the 4 lights
(brightness, x/y/z position, $insidesurffact
(brightness inside relative to outside), and
$lighttwosidedflag.
