1. A method for manipulating a curve object which generates a three-dimensional representation on a display coupled to a computer with a user actuated input controller for selectively positioning a cursor at a location on the display, comprising the steps of: a) displaying a three-dimensional representation of a virtual box sized and positioned to surround a portion of the three-dimensional representation on the display, the three-dimensional representation extending outside the virtual box, the virtual box having at least one active zone sensitive to the presence of the cursor; b) detecting the cursor's location over the at least one active zone; c) activating a control movement type specified by the at least one active zone under the cursor; d) responding to a reposition of the cursor by controlling the curve object to cause a manipulation of the portion of the three-dimensional representation surrounded by the virtual box; and e) re-displaying the three-dimensional representation in accordance with the manipulation defined in step (d).