# File easy_vtk.rb, line 971
  def sphere( radius, options={} )
    resolution = false
    opacity = false
    color = false
    wireframe = false
    options.each{ |key, val|
      case key
      when 'resolution'
        resolution = val
      when 'opacity'
        opacity = val
      when 'color'
        color = val
        if !(Array === color) || color.length != 3
          raise "color must be Array whose length is three"
        end
      when 'wireframe'
        wireframe = val
      else
        raise "option (#{key}) is invalid"
      end
    }
    sphere = Vtk::SphereSource.new
    sphere.SetRadius( radius )
    if resolution
      sphere.SetPhiResolution( resolution )
      sphere.SetThetaResolution( resolution )
    end
    mapper = Vtk::PolyDataMapper.new
    mapper.SetInput( sphere.GetOutput )
    actor = Vtk::Actor.new
    actor.SetMapper( mapper )
    actor.GetProperty.SetDiffuseColor( *color ) if color
    actor.GetProperty.SetOpacity( options['opacity'] ) if opacity
    actor.GetProperty.SetRepresentationToWireframe if wireframe
    @ren.AddActor( actor )
    return nil
  end