calc_spline - Calculates a series of values along a Bezier spline. Allegro game
programming library.
**#include <allegro.h>**
**void calc_spline(const int points[8], int npts, int *x, int
*y);**

Calculates a series of npts values along a Bezier spline, storing them in the
output x and y arrays. The Bezier curve is specified by the four x/y control
points in the points array: points[0] and points[1] contain the coordinates of
the first control point, points[2] and points[3] are the second point, etc.
Control points 0 and 3 are the ends of the spline, and points 1 and 2 are
guides. The curve probably won't pass through points 1 and 2, but they affect
the shape of the curve between points 0 and 3 (the lines p0-p1 and p2-p3 are
tangents to the spline). The easiest way to think of it is that the curve
starts at p0, heading in the direction of p1, but curves round so that it
arrives at p3 from the direction of p2. In addition to their role as graphics
primitives, spline curves can be useful for constructing smooth paths around a
series of control points, as in exspline.c.