Depth effects.
They are used by the Viewer3D object.
Values:
catClippingModeClear
The clear depth effect. All objects are displayed.
catClippingModeNear
The scene is clipped by the near plane only. Any object
between the eye and the near plane is not visible.
catClippingModeFar
The scene is clipped by the far plane only. Any object
beyond the far plane is not visible.
catClippingModeNearAndFar
The foggy depth effect. Fog is added in the background to
progressively dissimulate far objects. This increases the display
performance when a great number of objects are displayed.