Testing point in Polygon. Based on http://www.ecse.rpi.edu/~wrf/Research/Short_Notes/pnpoly.html

pnpoly

#include <stdio.h>
#include <string.h>
int pnpoly(int nvert, float *vertx, float *verty, float testx, float testy);

float buffx[3];
float buffy[3];

main()
{
    buffx[0] = 1.0; buffy[0] = 1.0;
    buffx[1] = 2.0; buffy[1] = 1.0;
    buffx[2] = 2.0; buffy[2] = 2.0;
    buffx[3] = 1.0; buffy[3] = 2.0;
    
    int result = pnpoly(3, buffx, buffy, 0, 0);
    printf("%d", result);
}


int pnpoly(int nvert, float *vertx, float *verty, float testx, float testy)
{
  int i, j, c = 0;
  for (i = 0, j = nvert-1; i < nvert; j = i++) {
    if ( ((verty[i]>testy) != (verty[j]>testy)) &&
     (testx < (vertx[j]-vertx[i]) * (testy-verty[i]) / (verty[j]-verty[i]) + vertx[i]) )
       c = !c;
  }
  return c;
}