We use P to also denote the region to the left of P and call this region the positive side of P . The number of vertices is called the size of P . A polygon with empty vertex sequence is called empty. Only the former guarantee correct results. There is a small number of operations that are only available for polygon .
P is initialized to the empty polygon.
P is initialized to the polygon with vertex sequence pl . If prec is zero, the implementation chooses prec large enough such that there is no loss of precision in the conversion. P translated by vector v . P translated by vector - v . Returns zero if P is empty.