It's ok if you don't reply If you don't have something to add to my saying. I think it is generated in like

for x in range(0, 90): for y in range(0, 90): if xx + yy < 90*90: # it is in circle

So for the each x, the one that has the greatest y will be the sin.

Something like floatrange(0,1,0.001) may work too.