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variable: $xrot -- rotate brain around x-axis
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keyboard equivalent: [Cmd/Alt]-up/down arrow
direct manip. equiv.: Shift-left-click-drag-up/down

The "xrot:" entry (lower left) rotates brain
surface around a horizontal axis (i.e., around
the x-axis) in degrees (positive rotates the top
side of the brain towards the viewer).

Clicking in the slider troughs rotates 1 degree.

In a tcl rendering script, this rotation can be
achieved with:

  rotate_brain_x <deg>
  redraw

If focus is on the brain surface window, the
up/down arrows rotate the brain -2/+2 degrees (in
the interface window, cmd-arrow is required to
avoid instead moving the cursor in an entry).

