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RuntimeError: CGContextRef is NULL with draw_artist #166
Description
Original report at SourceForge, opened Mon Oct 4 17:04:36 2010
draw_artist on mac os x gives me an error with the following script:
import numpy as np
import matplotlib.pyplot as plt
plt.ion()
plt.figure()
subplot = plt.subplot(1,1,1)
axis = plt.imshow(np.random.random((10,10)))
plt.draw()
subplot.draw_artist(axis)
plt.show()
The traceback is:
Traceback (most recent call last):
File "matplotlib-bug.py", line 8, in
subplot.draw_artist(axis)
File "/Volumes/Data/Local/lib/python2.7/site-packages/matplotlib/axes.py", line 1946, in draw_artist
a.draw(self._cachedRenderer)
File "/Volumes/Data/Local/lib/python2.7/site-packages/matplotlib/artist.py", line 55, in draw_wrapper
draw(artist, renderer, _args, *_kwargs)
File "/Volumes/Data/Local/lib/python2.7/site-packages/matplotlib/image.py", line 338, in draw
gc = renderer.new_gc()
File "/Volumes/Data/Local/lib/python2.7/site-packages/matplotlib/backends/backend_macosx.py", line 105, in new_gc
self.gc.save()
RuntimeError: CGContextRef is NULL
matplotlib version: 1.0.0 (compiled)
python version 2.7 (binary from python.org)
macosx version: 10.6.4
SourceForge Comments
On Tue Oct 5 02:39:48 2010, nicolasrougier wrote:
I got the code from the "Animating selected plot elements" from the scipy cookbook page on animation.
The reason for this code is that I've several subplots to be drawn while I'm running the simulation. I could have used a simple call to plt.draw() but this would redraw the whole figure (is that right ?) and thus I tried to restrict the re-drawing to changing elements since the display is quite slow compared to simualtion.
The same code seems to be working on linux using the gtk backend but maybe it is not supposed to.
On Tue Oct 5 01:31:15 2010, mdehoon wrote:
I think what is happening is that graphics context functions are being called outside of the event loop. This will not work (at least not in the Mac OS X backend), since the graphics context (CGContextRef) is initialized inside the event loop. What exactly are you trying to accomplish? Can you show a full script that you would like to use for your animations? Also, is this script shown in the matplotlib documentation somewhere?
SourceForge History
- On Tue Oct 5 01:31:15 2010, by mdehoon: assigned_to: 100
Activity
dmcdougall commented on Sep 23, 2012
Here's some workarounds:
Instead of calling plt.draw() to draw the whole figure. One can call plt.gca() to clear the axis, and then add the updated image to the axis with a call to plt.imshow(blah).
If you want to add a single artist, wouldn't a call to subplot.add_artist() suffice?
pelson commented on Sep 23, 2012
Looks like the original issue was @rougier. If you remember the scenario, would you be able to provide some more information (re @mdehoon and @dmcdougall 's questions). Thanks.
rougier commented on Sep 23, 2012
What do you mean by scenario ? If this is the original animation file, I'm not sure I still have the code.
For the original code, I think I use the one from http://www.scipy.org/Cookbook/Matplotlib/Animations (Animating selected plot elements)
astrofrog commented on Jun 24, 2013
@dmcdougall @pelson - I am running into the same issue with the following code:
import numpy as np import matplotlib matplotlib.use('MacOSX') from matplotlib import pyplot as plt fig = plt.figure() ax = fig.add_subplot(1,1,1) image = ax.imshow(np.random.random((128, 128))) def test_callback(event): ax.draw_artist(image) fig.canvas.mpl_connect('button_press_event', test_callback) plt.show()If I click anywhere in the axes (to trigger the callback) I get:
Traceback (most recent call last): File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/backend_bases.py", line 1785, in button_press_event self.callbacks.process(s, mouseevent) File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/cbook.py", line 527, in process proxy(*args, **kwargs) File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/cbook.py", line 405, in __call__ return mtd(*args, **kwargs) File "test_draw_artist.py", line 11, in test_callback ax.draw_artist(image) File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/axes.py", line 2098, in draw_artist a.draw(self._cachedRenderer) File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/artist.py", line 54, in draw_wrapper draw(artist, renderer, *args, **kwargs) File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/image.py", line 352, in draw gc = renderer.new_gc() File "/Users/tom/Library/Python/2.7/lib/python/site-packages/matplotlib-1.4.x-py2.7-macosx-10.6-x86_64.egg/matplotlib/backends/backend_macosx.py", line 97, in new_gc self.gc.save() RuntimeError: CGContextRef is NULLThis is specific to the MacOSX backend.
tacaswell commented on Aug 18, 2014
This is the same problem as #2654 and #1266 closing as we have those still open.