When the shift key is pressed on the keyboard,
horizontal mouse motion moves B-spline control points
\(P_i\) in the z-direction.
(This motion is not yet visible).
In the top half of the window draw the default view perpendicular to the x-y plane. In the bottom half of the window draw the side view perpendicular to y-z plane.
The double-view should be toggled when 4 is pressed.
NOTE: Picking needs only work in Single View.
On key 5 press toggle on-off a (suitably large) yellow dot traveling around the closed BB-curve (animation). Draw the tangent (red), normal (green) and bi-normal (blue) [Frenet frame] of the curve at the yellow dot.