/* ** Reproduced with thanks from mapper 1.2 ** 7/26/93 Kevin Hughes, kevinh@pulua.hcc.hawaii.edu ** polygon code copyright 1992 by Eric Haines, erich@eye.com */ #include <stdio.h> #define MAXLINE 500 #define MAXVERTS 100 #define X 0 #define Y 1 int pointinpoly(double point[2], double pgon[MAXVERTS][2]) { int i, numverts, inside_flag, xflag0; int crossings; double *p, *stop; double tx, ty, y; for (i = 0; pgon[i][X] != -1 && i < MAXVERTS; i++) ; numverts = i; crossings = 0; tx = point[X]; ty = point[Y]; y = pgon[numverts - 1][Y]; p = (double *) pgon + 1; if ((y >= ty) != (*p >= ty)) { if ((xflag0 = (pgon[numverts - 1][X] >= tx)) == (*(double *) pgon >= tx)) { if (xflag0) crossings++; } else { crossings += (pgon[numverts - 1][X] - (y - ty) * (*(double *) pgon - pgon[numverts - 1][X]) / (*p - y)) >= tx; } } stop = pgon[numverts]; for (y = *p, p += 2; p < stop; y = *p, p += 2) { if (y >= ty) { while ((p < stop) && (*p >= ty)) p += 2; if (p >= stop) break; if ((xflag0 = (*(p - 3) >= tx)) == (*(p - 1) >= tx)) { if (xflag0) crossings++; } else { crossings += (*(p - 3) - (*(p - 2) - ty) * (*(p - 1) - *(p - 3)) / (*p - *(p - 2))) >= tx; } } else { while ((p < stop) && (*p < ty)) p += 2; if (p >= stop) break; if ((xflag0 = (*(p - 3) >= tx)) == (*(p - 1) >= tx)) { if (xflag0) crossings++; } else { crossings += (*(p - 3) - (*(p - 2) - ty) * (*(p - 1) - *(p - 3)) / (*p - *(p - 2))) >= tx; } } } inside_flag = crossings & 0x01; return (inside_flag); }