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Qt4Agg backend changes figure size #9913
Description
Edit: Note that this issue is also still present with Qt5Agg and matplotlib 3.0.1
Showing a figure with Qt4Agg backend changes the figure size. This is observed with Windows 8.1, python 2.7, matplotlib 2.1.
import matplotlib
matplotlib.use("Qt4Agg")
import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1,2,4])
def update(evt):
print(fig.get_size_inches())
cid = fig.canvas.mpl_connect("key_press_event", update)
print(fig.get_size_inches())
plt.show()
The original figure is [ 6.4 4.8]. After the figure is drawn (and in this case you press a key), it is only [ 6.4 4.78].
One could argue that this is only a small amount, but saving the figure from within the event loop now gives a different figure size of the saved figure. To make this more obvious, consider the following code which saves a new image after each press of space.
import matplotlib
matplotlib.use("Qt4Agg")
import matplotlib.pyplot as plt
import numpy as np
class NextPlotter(object):
def __init__(self, fig, func, n):
self.__dict__.update(locals())
self.i = 0
self.cid = self.fig.canvas.mpl_connect("key_press_event", self.adv)
def adv(self, evt):
if evt.key == " " and self.i < self.n:
self.func(self.i)
self.i+=1
elif self.i >= self.n:
plt.close("all")
# Create data
pos = range(8)
scatterdata = np.random.normal(0, 5, size=(50,len(pos)))
#Create plot
fig, ax = plt.subplots()
ax.axis([-10,10,-10,10])
scatter = ax.scatter([], [], c="crimson", s=60)
# define updating function
def update(i):
print("++ update " + str(i))
scatter.set_offsets(np.c_[pos,scatterdata[i,:]])
fig.canvas.draw()
print(fig.get_size_inches())
plt.savefig("plot_{i}.png".format(i=i))
print(fig.get_size_inches())
# instantiate NextPlotter; press <space> to advance to the next image
c = NextPlotter(fig, update, len(scatterdata))
plt.show()
resulting in
Is this a problem of PyQt4? Can anyone reproduce this outside of Windows 8?
Activity
afvincent commentedon Dec 2, 2017
@ImportanceOfBeingErnest Thanks for the neat illustrations of the issue :).
I cannot reproduce this on Linux (Arch 4.13.12), with Python 2.7.11 (from conda) and Matplotlib 2.1.0 and master (from git), with the Qt5Agg and Qt4Agg backends. Would this suggest the problem to be a platform specific issue?
ImportanceOfBeingErnest commentedon Dec 2, 2017
I've done some further tests:
[ 6.4 4.78]and shrinks itself upon saving repeatedly.[ 8. 5.975]instead of[8. 6.]. But it does not shrink itself continuously using the second code from above.So there are actually 2 issues here: The fact that the figure is smaller in PyQt window is present throughout matplotlib versions. The fact that it shrinks each time it is saved is an issue with matplotlib 2 compared to matplotlib 1.5.
In any case it may be specific to Windows. (Unfortunately I can currently neither test with Linux, nor with PyQt5.)
jklymak commentedon Dec 2, 2017
Not an issue macOS python3, QT5 or macosx backends. (Sorry, can't test QT4 ;-). I've labelled as above...
tacaswell commentedon Dec 3, 2017
There is a feedback loop in the GUI code that resizes the MPL-figure to fit into the window (ex if you drag the window bigger) and if you resize the figure from python the size is forwarded to the GUI (which then may slightly re-size the
Figureto fit if there are rounding issues (ie, the requested size + dpi do not result in an integer number of pixels).bidhya commentedon Jan 1, 2018
I am not exactly sure, but I just started noticing the figures that were normal size now shrinks in Jupyter Notebook. I run this command to set figure size
%matplotlib inline import matplotlib.pyplot as plt plt.rcParams.update({'figure.figsize': (14, 6)})When I run this suite of code again, it seems to give the right sized figure as before. I am on Windows 10 with 32-bit Python 2.7 (Anaconda), and Matplotlib 2.1
tacaswell commentedon Jan 1, 2018
@bidhya Issues with the inline backend are probably un-related to this issue.
bidhya commentedon Jan 1, 2018
Thank you @tacaswell . I think the problem could be related new Pandas 0.22.0 which I updated this morning. Started noticing this change in plot size with Pandas plot functions.
kklmn commentedon Feb 10, 2018
I confirm the bug exists, it is Windows- and Qt-backend specific.
In Ubuntu 17.10 I don't have it with any backend and in Windows 10 with Tk backend I don't have it either.
In both Windows 10 and Ubuntu 17.10 I have
The problem is not directly related to Jupyter/Ipython. I typically run my scripts from Spyder (currently 3.2.6) in its IPython console, where I experience the problem. If I run a script from Spyder but in an external system terminal I do have the shrinkage with Qt5agg backend and don't have it with TkAgg.
A workaround for me is to do
fig.set_size_inches(size_inches)
after each fig.savefig. The size I save at the creation time as
size_inches = fig.get_size_inches()
workaround for figure size change
anntzer commentedon Feb 10, 2018
I think this may be effectively fixed (at least the repeated size changes upon savefig) by #10292?
7 remaining items
QuLogic commentedon Mar 27, 2020
Is this still a problem?
ImportanceOfBeingErnest commentedon Mar 27, 2020
While some of the tangential problems have been fixed in the meantime, the original problem is still present, that is, a figure that should be (6.4, 4.8) inches becomes (6.4, 4.78) inches when drawn with the QT backend on windows.
QuLogic commentedon Mar 28, 2020
At 100 dpi, 4-8-4.78 == 22 pixels, which is the size of the statusbar. We only check the size hint for that, and then calculate a window size from it; I'd guess that if you check https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/backends/backend_qt5.py#L573 the
sbs.height()would be 0.QuLogic commentedon May 15, 2020
The statusbar is removed in the default setup on master, so perhaps this is fixed now?
QuLogic commentedon Jun 3, 2021
Either way, we no longer support Qt4.