parameters: (self, point)
docstring: Set initial cursor window coordinates and pick constrain-axis.
docstring_summary: Set initial cursor window coordinates and pick constrain-axis.
docstring_tokens: Set initial cursor window coordinates and pick constrain - axis .
function: def down(self, point):
          """Set initial cursor window coordinates and pick constrain-axis."""
          self._vdown = arcball_map_to_sphere(point, self._center, self._radius)
          self._qdown = self._qpre = self._qnow
  
          if self._constrain and self._axes is not None:
              self._axis = arcball_nearest_axis(self._vdown, self._axes)
              self._vdown = arcball_constrain_to_axis(self._vdown, self._axis)
          else:
              self._axis = None
function_tokens: def down ( self , point ) : self . _vdown = arcball_map_to_sphere ( point , self . _center , self . _radius ) self . _qdown = self . _qpre = self . _qnow if self . _constrain and self . _axes is not None : self . _axis = arcball_nearest_axis ( self . _vdown , self . _axes ) self . _vdown = arcball_constrain_to_axis ( self . _vdown , self . _axis ) else : self . _axis = None