ON_3dVector ON_Light::PerpindicularDirection() const
{
// returns a consistent vector perpendicular to the
// light's direction. This vector is useful for
// user interface display.
ON_3dVector dir = m_direction;
if ( !dir.IsValid() || !dir.Unitize() )
return ON_UNSET_VECTOR;
ON_3dVector xdir;
if ( IsLinearLight() || IsRectangularLight() )
{
xdir = m_length;
if ( xdir.IsValid() && xdir.Unitize() && fabs(xdir*dir) <= ON_SQRT_EPSILON )
return xdir;
}
if( dir.IsParallelTo( ON_zaxis, ON_DEGREES_TO_RADIANS * 3.0))
xdir = ON_CrossProduct( dir, ON_xaxis);
else
xdir = ON_CrossProduct( dir, ON_zaxis);
xdir.Unitize();
ON_3dVector ydir = ON_CrossProduct(dir,xdir);
ydir.Unitize();
ON_3dVector right;
switch(dir.MaximumCoordinateIndex())
{
case 0:
right = (fabs(xdir.y) > fabs(ydir.y)) ? xdir : ydir;
if ( right.y < 0.0 )
right.Reverse();
break;
case 1:
case 2:
right = (fabs(xdir.x) > fabs(ydir.x)) ? xdir : ydir;
if ( right.x < 0.0 )
right.Reverse();
break;
default:
right = xdir;
break;
}
if ( right[right.MaximumCoordinateIndex()] < 0.0 )
right.Reverse();
return right;
}
