I wonder if the code is correct.

[imksc]

subcatch.c

1835 line

if (Polygon2D.clockwise == CLOCKWISE)
{
vnx = -(v2.y - v1.y);
vny = (v2.x - v1.x);

}
else {
vnx = (v2.y - v1.y);
vny = -(v2.x - v1.x);
}
M2DFace[j].vnx = vnx / (M2DFace[j].length * UCF(LENGTH));
M2DFace[j].vny = vny / (M2DFace[j].length * UCF(LENGTH));

Is not this?
vny = -(v2.y - v1.y);
vnx = (v2.x - v1.x);