判断点在多边形内部

int pnpoly(int nvert, float *vertx, float *verty, float testx, float testy) //testx,testy 是要判断的点
{
  int i, j, c = 0;
  for (i = 0, j = nvert-1; i < nvert; j = i++) //对于多边形相邻的两点
  {
    if ( ((verty[i]>testy) != (verty[j]>testy)) &&                   //根据上图
     (testx < (vertx[j]-vertx[i]) * (testy-verty[i]) / (verty[j]-verty[i]) + vertx[i]) )
       c = !c;
  }
  return c;
}

转自 http://www.javashuo.com/article/p-aektebzd-bg.html