/* Return -1, 0 or 1 depending on the relative slopes of two lines.  */
static int _cairo_slope_compare_sgn(double dx1, double dy1, double dx2, double dy2)
/* Return -1, 0 or 1 depending on the relative slopes of two lines.  */
static int _cairo_slope_compare_sgn(double dx1, double dy1, double dx2, double dy2)
{
    double  c = (dx1 * dy2 - dx2 * dy1);
    if (c > 0) return 1;
    if (c < 0) return -1;
    return 0;
}