Manipulate the parameters of a lookAt() created virtual camera. Note:
The eye location is at the center of the camera
The center location starts at the origin, which is also the
center of the widget. The center location is visible if you move
it away from the origin. Note how the camera is always pointed at this location.
The "up" vector is drawn as a black line segment.
Mouse drags will allow you to get different views of the left canvas window.
The scenes are rendered in perspective mode so you can sense depth.
The left canvas shows the relative location of the scene objects and the camera. The right
canvas shows the scene from the camera's vantage point.
Manipulate the function lookAt(M, eye_x, eye_y, eye_z,
center_x, center_y, center_z, up_dx, up_dy, up_dz)