C ++ determines whether a vertex is in a plane

Direct function:

Bool ctriobject: ptinpolygon (point P, point * ptpolygon, int ncount) {// Number of intersections int ncross = 0; For (INT I = 0; I <ncount; I ++) {Point P1 = ptpolygon [I]; point P2 = ptpolygon [(I + 1) % ncount]; // link the last vertex to the first vertex if (p1.y = p2.y) continue; If (P. Y <min (p1.y, p2.y) continue; If (P. y> = max (p1.y, p2.y) continue; // returns the X coordinate Double X = (double) (p. y-p1.y) * (double) (p2.x-p1.x)/(double) (p2.y-p1.y) + p1.x; // only count the intersection of P1P2 and P to the right if (x> P. x) {ncross ++; }}// the intersection is an even number. Return (ncross % 2 = 1) outside the polygon );}