al_calculate_spline - Allegro 5 API

       Calculates  a  Bézier  spline given 4 control points.  If thickness <= 0, then num_segments of points are
       required in the destination, otherwise twice as many are needed.  The destination buffer  should  consist
       of  regularly  spaced  (by  distance  of  stride  bytes)  doublets  of  floats,  corresponding to x and y
       coordinates of the vertices.

       Parameters:

       • dest - The destination buffer

       • stride - Distance (in bytes) between starts of successive pairs of coordinates

       • points - An array of 4 pairs of coordinates of the 4 control points

       • thickness - Thickness of the spline ribbon

       • num_segments - The number of points to calculate

       al_calculate_spline - Allegro 5 API

al_draw_spline(3alleg5), al_calculate_arc(3alleg5), al_calculate_ribbon(3alleg5)

Allegro reference manual                                                            al_calculate_spline(3alleg5)

              #include <allegro5/allegro_primitives.h>

              void al_calculate_spline(float* dest, int stride, const float points[8],
                 float thickness, int num_segments)