Takes the ray defined by ‹p0› and ‹p1› and partitions it into zero or more sub-intervals where each interval intersects a cluster of metaballs from ‹filename›. The interval may not actually intersect any metaballs, but will provide fairly tight bounds on the cluster.

This allows a ray-marching algorithm to “skip” uninteresting areas and only focus on marching through areas where metaballs might be found.

The first time you call the function, use ‹index›=-1 and set ‹p0› and ‹p1› to the endpoints of the ray. If the function finds an interval, it returns 1 and sets ‹p0› and ‹p1› to the endpoints of the interval and increments ‹index›. Otherwise it returns 0 and doesn’t alter the arguments.

So, you can repeatedly call the function with variables for the ‹index›, ‹index›, and ‹index› arguments to ray-march through areas of interest, skipping the dead space:

int    index;
vector    p0, p1;
// Initialize input values
index = -1;
p0 = Eye; p1 = P;
result = 0;
while (metamarch(index, metaball_file, p0, p1, displace_bound))
{
result += ray_march(metaball_file, p0, p1);
}