ON_3dVector ON_Polyline::SegmentDirection( int segment_index ) const
{
ON_3dVector v;
if ( segment_index >= 0 && segment_index < m_count-1 ) {
v = m_a[segment_index+1] - m_a[segment_index];
}
else {
v.Zero();
}
return v;
}
ON_BOOL32
ON_Surface::EvNormal( // returns false if unable to evaluate
double s, double t, // evaluation parameters (s,t)
ON_3dPoint& point, // returns value of surface
ON_3dVector& ds, // first partial derivatives (Ds)
ON_3dVector& dt, // (Dt)
ON_3dVector& normal, // unit normal
int side, // optional - determines which side to evaluate from
// 0 = default
// 1 from NE quadrant
// 2 from NW quadrant
// 3 from SW quadrant
// 4 from SE quadrant
int* hint // optional - evaluation hint (int[2]) used to speed
// repeated evaluations
) const
{
// simple cross product normal - override to support singular surfaces
ON_BOOL32 rc = Ev1Der( s, t, point, ds, dt, side, hint );
if ( rc ) {
const double len_ds = ds.Length();
const double len_dt = dt.Length();
// do not reduce the tolerance used here - there is a retry in the code
// below.
if ( len_ds > ON_SQRT_EPSILON*len_dt && len_dt > ON_SQRT_EPSILON*len_ds )
{
ON_3dVector a = ds/len_ds;
ON_3dVector b = dt/len_dt;
normal = ON_CrossProduct( a, b );
rc = normal.Unitize();
}
else
{
// see if we have a singular point
double v[6][3];
int normal_side = side;
ON_BOOL32 bOnSide = false;
ON_Interval sdom = Domain(0);
ON_Interval tdom = Domain(1);
if (s == sdom.Min()) {
normal_side = (normal_side >= 3) ? 4 : 1;
bOnSide = true;
}
else if (s == sdom.Max()) {
normal_side = (normal_side >= 3) ? 3 : 2;
bOnSide = true;
}
if (t == tdom.Min()) {
normal_side = (normal_side == 2 || normal_side == 3) ? 2 : 1;
bOnSide = true;
}
else if (t == tdom.Max()) {
normal_side = (normal_side == 2 || normal_side == 3) ? 3 : 4;
bOnSide = true;
}
if ( !bOnSide )
{
// 2004 November 11 Dale Lear
// Added a retry again with a more generous tolerance
if ( len_ds > ON_EPSILON*len_dt && len_dt > ON_EPSILON*len_ds )
{
ON_3dVector a = ds/len_ds;
ON_3dVector b = dt/len_dt;
normal = ON_CrossProduct( a, b );
rc = normal.Unitize();
}
else
{
rc = false;
}
}
else {
rc = Evaluate( s, t, 2, 3, &v[0][0], normal_side, hint );
if ( rc ) {
rc = ON_EvNormal( normal_side, v[1], v[2], v[3], v[4], v[5], normal);
}
}
}
}
if ( !rc ) {
normal.Zero();
}
return rc;
}
