def draw_gl( self ):
n = self.n
r = self.r
vt = Vec( 1,2,3 ).norm()
if vt == n:
vt = Vec( 3,2,1 ).norm()
v1 = vt.vcross( n )
v2 = v1.vcross( n )
v1,v2,v3,v4 = r + v1+v2, r + v1-v2, r + v2-v1, r -v1-v2
glBegin( GL_LINES )
glVertex3f( *v1 )
glVertex3f( *v4 )
glVertex3f( *v2 )
glVertex3f( *v3 )
glVertex3f( *v1 )
glVertex3f( *v2 )
glVertex3f( *v1 )
glVertex3f( *v3 )
glVertex3f( *v3 )
glVertex3f( *v4 )
glVertex3f( *v2 )
glVertex3f( *v4 )
glEnd( )
