To do more than two points just step through the array of points using the previous point, the current point and the next two points as the four points for the spline. For each of these segments draw a curve for 0<t<1. This curve will be between the current point and the next point.
The code to draw the spine is:
Code:
var i;
for(i=0; i<3; i++)
{
for(f = 0; f <= 1.0; f += 0.01)
{
draw_line(vec_to_catmull(pos, pt[cycle(i-1,0,4)], pt[cycle(i,0,4)], pt[cycle(i+1,0,4)], pt[cycle(i+2,0,4)], f), COLOR_RED, 100);
}
}
