HOW TO: Draggable legend in matplotlib
- by Adam Fraser
QUESTION:
I'm drawing a legend on an axes object in matplotlib but the default positioning which claims to place it in a smart place doesn't seem to work. Ideally, I'd like to have the legend be draggable by the user. How can this be done?
SOLUTION:
Well, I found bits and pieces of the solution scattered among mailing lists. I've come up with a nice modular chunk of code that you can drop in and use... here it is:
class DraggableLegend:
def __init__(self, legend):
self.legend = legend
self.gotLegend = False
legend.figure.canvas.mpl_connect('motion_notify_event', self.on_motion)
legend.figure.canvas.mpl_connect('pick_event', self.on_pick)
legend.figure.canvas.mpl_connect('button_release_event', self.on_release)
legend.set_picker(self.my_legend_picker)
def on_motion(self, evt):
if self.gotLegend:
dx = evt.x - self.mouse_x
dy = evt.y - self.mouse_y
loc_in_canvas = self.legend_x + dx, self.legend_y + dy
loc_in_norm_axes = self.legend.parent.transAxes.inverted().transform_point(loc_in_canvas)
self.legend._loc = tuple(loc_in_norm_axes)
self.legend.figure.canvas.draw()
def my_legend_picker(self, legend, evt):
return self.legend.legendPatch.contains(evt)
def on_pick(self, evt):
if evt.artist == self.legend:
bbox = self.legend.get_window_extent()
self.mouse_x = evt.mouseevent.x
self.mouse_y = evt.mouseevent.y
self.legend_x = bbox.xmin
self.legend_y = bbox.ymin
self.gotLegend = 1
def on_release(self, event):
if self.gotLegend:
self.gotLegend = False
...and in your code...
def draw(self):
ax = self.figure.add_subplot(111)
scatter = ax.scatter(np.random.randn(100), np.random.randn(100))
legend = DraggableLegend(ax.legend())
I emailed the Matplotlib-users group and John Hunter was kind enough to add my solution it to SVN HEAD.
On Thu, Jan 28, 2010 at 3:02 PM, Adam
Fraser
wrote:
I thought I'd share a solution to the draggable legend problem since
it took me forever to assimilate all the scattered knowledge on the
mailing lists...
Cool -- nice example. I added the code to
legend.py. Now you can do
leg = ax.legend() leg.draggable()
to enable draggable mode. You can
repeatedly call this func to toggle
the draggable state.
I hope this is helpful to people working with matplotlib.
