Infection Animation

        float speed = chf('speed');
float t = @Time * speed;

int i = floor(t);
float u = frac(t);
int n = npointsgroup(0, 'start');

string att = 'dist_' + itoa(i%n);
float dist = point(0, att, i@ptnum);

float mask = chramp('shape', dist - u + 1.0);
float fade = 1.0 - smooth(0.5, 1.0, u);

f@mask = mask * fade;
setdetailattrib(0, 'active_dist', att, 'set');