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Qt5 Segfaults on window resize #11728

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jklymak opened this issue Jul 21, 2018 · 2 comments · Fixed by #11731
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Qt5 Segfaults on window resize #11728

jklymak opened this issue Jul 21, 2018 · 2 comments · Fixed by #11731
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@anntzer
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GUI: Qt Release critical For bugs that make the library unusable (segfaults, incorrect plots, etc) and major regressions.
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v3.0.0

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@jklymak
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jklymak commented Jul 21, 2018 •
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Bug report

On my machine using master I can reliably get segfaults using QT5Agg by resizing the window a bunch of times (say order 20). There is no segfault on v2.2.2 Suspect #11712 and/or #8951. (Sorry, not quite sure how to revert those locally to test).

python3.6_2018-07-21-150850_JMKMBP.crash.zip

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
plt.show()

Matplotlib version

  • Operating system: macOS 10.13.6
  • Matplotlib version: master as of this AM.
  • Matplotlib backend (print(matplotlib.get_backend())): Qt5Agg
  • Python version: 3.6.3
@jklymak jklymak added this to the v3.0 milestone Jul 21, 2018
@jklymak jklymak added Release critical For bugs that make the library unusable (segfaults, incorrect plots, etc) and major regressions. GUI: Qt labels Jul 21, 2018
@anntzer
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anntzer commented Jul 21, 2018

Does

diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
index 6e0e964a8..b009187a4 100644
--- a/lib/matplotlib/backends/backend_qt5agg.py
+++ b/lib/matplotlib/backends/backend_qt5agg.py
@@ -48,10 +48,9 @@ class FigureCanvasQTAgg(FigureCanvasAgg, FigureCanvasQT):
             [[left, self.renderer.height - (top + height * self._dpi_ratio)],
              [left + width * self._dpi_ratio, self.renderer.height - top]])
         reg = self.copy_from_bbox(bbox)
-        buf = reg.to_string_argb()
+        buf = memoryview(reg)
         qimage = QtGui.QImage(
-            buf, width * self._dpi_ratio, height * self._dpi_ratio,
-            QtGui.QImage.Format_ARGB32)
+            buf, buf.shape[1], buf.shape[0], QtGui.QImage.Format_RGBA8888)
         if hasattr(qimage, 'setDevicePixelRatio'):
             # Not available on Qt4 or some older Qt5.
             qimage.setDevicePixelRatio(self._dpi_ratio)

fix it for you? Basically the problem is that the bbox extents are floats, so there may be an off-by-one difference in rounding to get the image size. Format_RGBA8888 may appear as less efficient but in fact we save a copy by directly taking the underlying renderer buffer in memoryview(reg) so it comes down to the same.

@jklymak
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jklymak commented Jul 21, 2018

Seems to, at least to the extent that I got bored of resizing the window w/ the GUI well past the point where I could make it die w/o that patch...

@anntzer anntzer mentioned this issue Jul 21, 2018
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GUI: Qt Release critical For bugs that make the library unusable (segfaults, incorrect plots, etc) and major regressions.
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Directly get the size of the renderer buffer from the renderer. anntzer/matplotlib
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@anntzer @jklymak