bbox -100,-100,200,200,true

l = 99.9;

wall (-1, 0,  1*l), -1*l, 1*l, green
wall ( 1, 0,  1*l), -1*l, 1*l, green

wall ( 0,-1,  1*l), -1*l, 1*l, green
wall ( 0, 1,  1*l), -1*l, 1*l, green

bmin = -0.8*l;
bmax =  0.8*l;
rr = (bmax-bmin)/10;
d = 0.49*rr;

balltype t1, d, 1, black

ball (-0.8*l,0), (0.4*l,0.4*l*randn), t1