This is a snippet I found on the internet a while ago, seemed to work fine for everything I threw at it.

Don't ask me about the math behind it ;)

xp and yp are point to an array of corners, x,y is the point you want to check:

template < typename T > bool is_point_in_poly( int num_edges, T *xp, T *yp, T x, T y) { int i, j; bool c = 0; for (i = 0, j = num_edges-1; i < num_edges; j = i++) { if ((((yp[i]<=y) && (y<yp[j])) || ((yp[j]<=y) && (y<yp[i]))) && (x < (xp[j] - xp[i]) * (y - yp[i]) / (yp[j] - yp[i]) + xp[i])) c = !c; } return c; }