Winding method for finding whether a point is contained by a 2D polygon defined by a vertex loop (C#/Unity)

IsPointInside.cs

public static bool IsPointInside (Vector2 point, Vector2[] polygonBoundary)
{
    int i = 0, j = 1;
    int retval = 0;
    while (j < polygonBoundary.Length)
    {
        var pointI = polygonBoundary[i];
        var pointJ = polygonBoundary[j];
        int side = (pointJ.x - pointI.x) * (point.y - pointI.y) - (point.x -  pointI.x) * (pointJ.y - pointI.y);
        int upward   = ((side > 0) & (pointI.y <= point.y) & (pointJ.y >  point.y)) ? +1 : 0;
        int downward = ((side < 0) & (pointI.y  > point.y) & (pointJ.y <= point.y)) ? -1 : 0;
        ++i;
        ++j;
        retval += upward;
        retval += downward;
    }
    return retval != 0;
}

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