-------------------------------------------
tcl functs (left-click): make interface size popup
  mini, mini2, mini3, macro, micro
  keyboard equiv: <[fn-]F1 to [fn-]F5>
-------------------------------------------
tcl bind (mid-click): invert contrast
  set bwslope [expr -$bwslope]
    => toggle sing of $bwslope ("midpt:")
-------------------------------------------

Left-clicking the small "i" button at the extreme
left makes small pop-up for controlling size and
arrangement of the tkmedit tools interface.

The interface size can also be controlled with
using the [fn-]F1 to [fn-]F5 buttons (focus must
be in the tkmedit tools window).

Interface sizes

  F1 -- default interface (basic editing)
  F2 -- add functional overlay tools (right)
  F3 -- add ramp, spherical edit tools (bottom right)
  F4 -- everything (EEG, cortical ribbon colors, 2D color)
  F5 -- minmal, long thin (e.g., to edit cerebellum)

-------------------------------------------
tcl bind (mid-click): invert contrast
  set bwslope [expr -$bwslope]
    => toggle sing of $bwslope ("midpt:")
-------------------------------------------

A non-default middle-click of the "i" button
toggles the sign of $bwslope ("midpt:").  When
$bwslope is negative, contrast is inverted
(default is positive).

