public function setBlockSkyLight($x, $y, $z, $level)
{
$i = $x << 10 | $z << 6 | $y >> 1;
$old_sl = ord($this->skyLight[$i]);
if (($y & 1) === 0) {
$this->skyLight[$i] = chr($old_sl & 0xf0 | $level & 0xf);
} else {
$this->skyLight[$i] = chr(($level & 0xf) << 4 | $old_sl & 0xf);
}
$this->hasChanged = true;
}