“…They are used for the design of curves and they are the starting point for several generalizations [1,6,7,12,13,17,[19][20][21][22][23]25,26]: in particular to higher dimensions and to B-splines. Powerful algorithms are available for both their algebraic construction and their visualization, and their basic theory (explained beautifully in Farin's book [5]) has been examined repeatedly from different new angles: see, e.g., for the "basis function" point of view, many bases are presented in new spaces other than the polynomial space [12,13,19,20,22,25,26], [1] for the "natural generalization of Bézier curves", [7] for "barycentric" and [21] for "blossoming". Although these algorithms are very effective and widely used in practice, they have a drawback: they are not able to control the shape of the corresponding curves keeping the control polygon unchanged.…”