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computer graphics c version phần 6

Căng thẳng tham số t có giải thích tương tự như trong việc xây dựng Đức Hồng Y-spline, có nghĩa là, nó điều khiển chùng xuống, độ kín của các phần đường cong. Bias (b) được sử dụng để điều chỉnh số lượng đường cong uốn cong ở mỗi đầu của phần một, | Simpo PDF Merge and Split Unregistered Version - http www.simpopdf.com t 0 Looser Curve X. Figure 10-31 4 Effect of the tension parameter on t 0 the shape of a cardinal spline Tighter Curve section. Tension parameter t has the same interpretation as in the cardinal-spline formulation that is it controls the looseness or tightness of the curve sections. Bias b is used to adjust the amount that the curve bends at each end of a section so that curve sections can be skewed toward one end or the other Fig. 10-33 . Parameter c controls the continuity of the tangent vector across the boundaries of sections. If c is assigned a nonzero value there is a discontinuity in the slope of the curve across section boundaries. Kochanek-Bartel splines were designed to model animation paths. In particular abrupt changes in motion of a object can be simulated with nonzero values for parameter c. Figure 10-32 The cardina 326 Simpo PDF Merge and Split Unregistered Version - http www.simpopdf.com Section 10-8 BEZIER CURVES AND SURFACES This spline approximation method was developed by the French engineer Pierre Bezier for use in the design of Renault automobile bodies. Bézier splines have a number of properties that make them highly useful and convenient for curve and surface design. They are also easy to implement. For these reasons Bézier splines are widely available in various CAD systems in general graphics packages such as GL on Silicon Graphics systems and in assorted drawing and painting packages such as Aldus SuperPaint and Cricket Draw . Bézier Curves In general a Bezier curve section can be fitted to any number of control points. The number of control points to be approximated and theứ relative position determine the degree of the Bezier polynomial. As with the interpolation splines a Bezier curve can be specified with boundary conditions with a characterizing matrix or with blending functions. For general Bezier curves the blending-function specification is the most convenient.