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inline int
isLeft( CPoint *P0, CPoint *P1, CPoint *P2 )
{
return ( (P1->x - P0->x) * (P2->y - P0->y)
- (P2->x - P0->x) * (P1->y - P0->y) );
}
bool CPointInPolygonDlg::PointPolygonAlgorithm(CPoint *pt)
{
int wn = 0; // the winding number counter
int j=0;
std::vector<CPoint *>::iterator it;
// loop through all edges of the polygon
for (it=vPolygon.begin(); it<vPolygon.end()-1; it++)// edge from V[i] to V[i+1]
{
j++;
if ((*(it))->y <= pt->y) { // start y <= pt->y
if ((*(it+1))->y > pt->y) // an upward crossing
if (isLeft( *it, *(it+1), pt) > 0) // P left of edge
++wn; // have a valid up intersect
}
else { // start y > P.y (no test needed)
if ((*(it+1))->y <= pt->y) // a downward crossing
if (isLeft( *it, *(it+1), pt) < 0) // P right of edge
--wn; // have a valid down intersect
}
}
if (wn==0)
return false;
return true;
}
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