[Matplotlib-users] Animating plots with the Qt backend

[Gerald S. <gd...@mr...>]

Hello,

I've been trying to animate some plots with the qt backend and run into 
a couple of problems.

Firstly,
I'd like to be able to update the axis limits in an automated fashion as 
the data changes size.

Secondly,
Resizing figures appears to redraw everything _but_ items with the 
animation flag.  The is causing me problems when the animation is paused 
or the frames are occurring slow enough such that there is a noticable 
period where the my lines disappear.

I've sort of solved both of these problems but the solutions seem 
hackish.  In particular updating the axis limits is slowing the 
animation by 25% and toggling the animated field using the qt events 
just feels like its asking for trouble.

Below is the qt animation example with my solutions.  Adjust the size of 
the plot after the animation finishes to see the effect of the resize 
hack.  I would be grateful if anyone could suggest some improvements.

Thanks,
Gerald.

# For detailed comments on animation and the techniqes used here, see

# the wiki entry http://www.scipy.org/Cookbook/Matplotlib/Animations

import os

import sys

#import matplotlib

#matplotlib.use('Qt4Agg')

from matplotlib.figure import Figure

from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas

from PyQt4 import QtCore, QtGui

ITERS = 100

import numpy as np

import time

class BlitQT(FigureCanvas):

     def __init__(self):

         FigureCanvas.__init__(self, Figure())

         self.ax = self.figure.add_subplot(111)

         #self.ax.grid()

         self.draw()

         self.old_size = self.ax.bbox.width, self.ax.bbox.height

         self.ax_background = self.copy_from_bbox(self.ax.bbox)

         self.cnt = 0

         self.x = np.arange(0,2*np.pi,0.01)

         self.sin_line, = self.ax.plot(self.x, np.sin(self.x), animated=True)

         self.cos_line, = self.ax.plot(self.x, np.cos(self.x), animated=True)

         self.draw()

         self.old_limits = self.ax.get_xlim(),self.ax.get_ylim()

         self.tstart = time.time()

         self.maintimer = self.startTimer(10)

     ## HACK for disapearing objects on resize

     def resizeEvent(self,evt):

         super(BlitQT,self).resizeEvent(evt)

         self.sin_line.set_animated(False)

     def paintEvent(self,evt):

         super(BlitQT,self).paintEvent(evt)

         self.sin_line.set_animated(True)

     def timerEvent(self, evt):

         current_size = self.ax.bbox.width, self.ax.bbox.height

         if self.old_size != current_size:

             self.old_size = current_size

             #self.ax.clear()

             #self.ax.grid()

             self.draw()

             self.ax_background = self.copy_from_bbox(self.ax.bbox)

         self.restore_region(self.ax_background)

         # update the data

         self.sin_line.set_ydata(np.sin(self.x+self.cnt/10.0)*self.cnt/100.0)

         self.cos_line.set_ydata(np.cos(self.x+self.cnt/10.0)*self.cnt/100.0)

         ## HACK for updating axis limits

         self.ax.relim()

         self.ax.autoscale_view()

         current_limits = self.ax.get_xlim(),self.ax.get_ylim()

         if self.old_limits != current_limits:

             self.old_limits = current_limits

             self.draw()

             self.ax_background = self.copy_from_bbox(self.ax.bbox)

             self.blit(self.figure.bbox)

          

         # just draw the animated artist

         self.ax.draw_artist(self.sin_line)

         self.ax.draw_artist(self.cos_line)

         # just redraw the axes rectangle

         self.blit(self.ax.bbox)

         if self.cnt == 0:

             # TODO: this shouldn't be necessary, but if it is excluded the

             # canvas outside the axes is not initially painted.

             self.draw()

         if self.cnt==ITERS:

             # print the timing info and quit

             print 'FPS:' , ITERS/(time.time()-self.tstart)

             #sys.exit()

             self.killTimer(self.maintimer)

         else:

             self.cnt += 1

app = QtGui.QApplication(sys.argv)

widget = BlitQT()

widget.show()

sys.exit(app.exec_())