Parametric curve evaluation method and apparatus for a computer graphics

Abstract

A method and apparatus for evaluating and rendering parametric curves such as non-uniform rational b-spline (NURBS) curves. NURBS data consisting of control point data, knot values and other data defining a curve is stored in system memory as a sequence of records such that successive spans of the curve are defined by successive individual data records in conjunction with a predetermined number of immediately preceding data records of the sequence. A graphics control processor transforms the control point data from modelling coordinates to view coordinates, converts the transformed control point data to homogeneous coordinates, and generates parameter points along the curve. Parallel floating point processors simultaneously evaluate the homogeneous coordinates of the curve at each parameter point along the curve using the Cox-de Boor procedure. A further floating point processor converts the homogeneous coordinates to geometric coordinates for subsequent rendering and display of the curve.