（zz）点在多边形内部判断算法（不限凹凸）

http://local.wasp.uwa.edu.au/~pbourke/geometry/insidepoly/

利用点和其中每个边的关系来判断

#define MIN(x,y) (x < y ? x : y) #define MAX(x,y) (x > y ? x : y) #define INSIDE 0 #define OUTSIDE 1 typedef struct { double x,y; } Point; int InsidePolygon(Point *polygon,int N,Point p) { int counter = 0; int i; double xinters; Point p1,p2; p1 = polygon[0]; for (i=1;i<=N;i++) { p2 = polygon[i % N]; if (p.y > MIN(p1.y,p2.y)) { if (p.y <= MAX(p1.y,p2.y)) { if (p.x <= MAX(p1.x,p2.x)) { if (p1.y != p2.y) { xinters = (p.y-p1.y)*(p2.x-p1.x)/(p2.y-p1.y)+p1.x; if (p1.x == p2.x || p.x <= xinters) counter++; } } } } p1 = p2; } if (counter % 2 == 0) return(OUTSIDE); else return(INSIDE); }