1 #! /usr/bin/env python
   2 # -*- coding: utf-8 -*-
   3 
   4 from matplotlib         import pylab as p
   5 from matplotlib.text	import Text
   6 
   7 
   8 class DragHandler(object):
   9     """ A simple class to handle Drag n Drop.
  10 
  11     This is a simple example, which works for Text objects only.
  12     """
  13     def __init__(self, figure=None) :
  14         """ Create a new drag handler and connect it to the figure's event system.
  15         If the figure handler is not given, the current figure is used instead
  16         """
  17 
  18         if figure is None : figure = p.gcf()
  19         # simple attibute to store the dragged text object
  20         self.dragged = None
  21 
  22         # Connect events and callbacks
  23         figure.canvas.mpl_connect("pick_event", self.on_pick_event)
  24         figure.canvas.mpl_connect("button_release_event", self.on_release_event)
  25 
  26     def on_pick_event(self, event):
  27         " Store which text object was picked and were the pick event occurs."
  28 
  29         if isinstance(event.artist, Text):
  30             self.dragged = event.artist
  31             self.pick_pos = (event.mouseevent.xdata, event.mouseevent.ydata)
  32         return True
  33 
  34     def on_release_event(self, event):
  35         " Update text position and redraw"
  36 
  37         if self.dragged is not None :
  38             old_pos = self.dragged.get_position()
  39             new_pos = (old_pos[0] + event.xdata - self.pick_pos[0],
  40                        old_pos[1] + event.ydata - self.pick_pos[1])
  41             self.dragged.set_position(new_pos)
  42             self.dragged = None
  43             p.draw()
  44         return True
  45 
  46 
  47 # Usage example
  48 from numpy import *
  49 
  50 # Create arbitrary points and labels
  51 x, y = random.normal(5, 2, size=(2, 9))
  52 labels = [ "Point %d" % i for i in xrange(x.size)]
  53 
  54 # trace a scatter plot
  55 p.scatter(x, y)
  56 p.grid()
  57 
  58 # add labels and set their picker attribute to True
  59 for a,b,l in zip(x,y, labels):
  60     p.text(a, b, l, picker=True)
  61 
  62 # Create the event hendler 
  63 dragh = DragHandler()
  64 
  65 p.show()
  66 
  67 # vim: set et: