chaco line plots with line labels on hover

hover_line_plots.py

from numpy import array, inf, linspace
from scipy.special import jn

from chaco.api import ArrayDataSource, ArrayPlotData, DataLabel, Plot
from chaco.tools.api import SimpleInspectorTool
from enable.api import BaseTool, ComponentEditor
from traits.api import HasTraits, Instance, on_trait_change
from traitsui.api import Item, View


class HoverLinePlots(HasTraits):

    inspector = Instance(SimpleInspectorTool)

    label = Instance(DataLabel)

    plot = Instance(Plot)

    @on_trait_change('inspector:new_value')
    def handle_inspection(self, value):
        point = self.inspector.last_mouse_position
        if point:
            # run through all the plots in the Plot and find closest within threshhold
            best = None
            best_distance = inf
            # inspector is attached to Plot, so we need to adjust screen coords
            # to take into account padding
            adjusted_point = (
                point[0] - self.plot.padding[0],
                point[1] - self.plot.padding[1]
            )
            for name, plots in self.plot.plots.items():
                for renderer in plots:
                    result = renderer.hittest(adjusted_point, return_distance=True)
                    if result is not None and result[-1] < best_distance:
                        best = name
                        best_distance = result[-1]

            # adjust label text and position (or hide if nothing)
            if best is not None:
                self.label.label_text = best
                self.label.data_point = array([value['x'], value['y']])
                self.label.visible = True
            else:
                self.label.visible = False

        self.label.invalidate_and_redraw()

    def __init__(self, **traits):
        super(HoverLinePlots, self).__init__(**traits)
        self.init()

    def init(self):
        """ Set up the plot inspector and label. """
        x = linspace(0.0, 10.0, 100)
        data = ArrayPlotData(
            x=ArrayDataSource(x, 'ascending'),
        )
        for i in range(10):
            data.set_data('j{}'.format(i), jn(x, i))

        self.plot = Plot(data)
        for i in range(10):
            y_name = 'j{}'.format(i)
            self.plot.plot(('x', y_name), name=y_name, color='auto')

        self.inspector = SimpleInspectorTool(self.plot)
        self.plot.tools.append(self.inspector)

        self.label = DataLabel(
            self.plot,
            visible=False,
            label_style='bubble',
            corner_radius=5,
            marker_visible=False,
            show_label_coords=False,
            border_width=0,
            bgcolor=(0.5, 0.5, 0.5, 0.5),
        )
        self.plot.overlays.append(self.label)

    traits_view = View(
        Item('plot', show_label=False, editor=ComponentEditor()),
        resizable=True,
    )


if __name__ == '__main__':
    hpl = HoverLinePlots()
    hpl.configure_traits()