sub trajectory(@) {
	# read parsed start pos, end pos, time
	my ($xstart, $xend, $time) = @_;

	use constant GRAVITY => 4;
	my $xmove = $xend - $xstart;
	my $xvel = $xmove / $time;

	my $yinitvel = GRAVITY*$time/2;
	my $ystart = 0;

	# return y=at^2 + bt + c, x = dt + e as (a,b,c,d,e)
	return (-&GRAVITY, $yinitvel, $ystart, $xvel, $xstart);
}
1;