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Add backend for Qt6 (support for PyQt6, PySide6) #19674

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Add backend for Qt6 (support for PyQt6, PySide6) #19674

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mfitzp
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@mfitzp mfitzp commented Mar 9, 2021

PR Summary

This PR adds support for Qt6, with support for both PyQt6 and PySide6 libraries.

For the most part PySide6 is source-compatible with PySide2, aside from the imports and some small changes (see below). PyQt6 is quite different. The main changes that affect us here are

  • Enums are no longer available at the top level of modules/objects. For example, previously Qt.GlobalColor.white was previously available as Qt.white. This short style was present in PyQt5 & PySide2 and is still supported in PySide6. PySide6 also supports the longer version (but...)
  • While enum types are identical between PyQt6 & PySide6, flag types have different names. So Qt.GlobalColor.white (enum) is the same in both. But alignment flags are in Qt.Alignment.AlignLeft in PyQt6 and Qt.AlignmentFlag.AlignLeft in PySide6.
  • (this may be a bug) Mouse events in PyQt6 no longer have the .pos() attribute. We can use .position() instead.
  • PyQt6 no longer supports using exec_(), must use exec(). PySide6 is exactly the reverse.
  • Qt.MidButton is now Qt.MiddleButton

The code to work around these differences is in qt_compat.py. Because of the differences in flag naming, I've opted to just copy the entries from the enums/flags to the parent object (matching PyQt5/PySide2). There is a further shim for QDialog to account for PyQt no longer having exec_().

Since this adds new files, the diff doesn't show the changes. Below is a diff between v5 and v6.

backends (qt6-backend) $ diff backend_qt5.py backend_qt6.py
158c158
<                     "PyQt4", "sip", "PySide", "PySide2", "Shiboken"])
---
>                     "PyQt4", "sip", "PySide", "PySide2", "PySide6", "Shiboken"])
205c205
<                QtCore.Qt.MidButton: MouseButton.MIDDLE,
---
>                QtCore.Qt.MiddleButton: MouseButton.MIDDLE,
279c279
<             x, y = self.mouseEventCoords(event.pos())
---
>             x, y = self.mouseEventCoords(event.position())
306c306
<         x, y = self.mouseEventCoords(event.pos())
---
>         x, y = self.mouseEventCoords(event.position())
313c313
<         x, y = self.mouseEventCoords(event.pos())
---
>         x, y = self.mouseEventCoords(event.position())
321c321
<         x, y = self.mouseEventCoords(event)
---
>         x, y = self.mouseEventCoords(event.position())
325c325
<         x, y = self.mouseEventCoords(event)
---
>         x, y = self.mouseEventCoords(event.position())
331,351c331,340
<     if QtCore.qVersion() >= "5.":
<         def wheelEvent(self, event):
<             x, y = self.mouseEventCoords(event)
<             # from QWheelEvent::delta doc
<             if event.pixelDelta().x() == 0 and event.pixelDelta().y() == 0:
<                 steps = event.angleDelta().y() / 120
<             else:
<                 steps = event.pixelDelta().y()
<             if steps:
<                 FigureCanvasBase.scroll_event(
<                     self, x, y, steps, guiEvent=event)
<     else:
<         def wheelEvent(self, event):
<             x = event.x()
<             # flipy so y=0 is bottom of canvas
<             y = self.figure.bbox.height - event.y()
<             # from QWheelEvent::delta doc
<             steps = event.delta() / 120
<             if event.orientation() == QtCore.Qt.Vertical:
<                 FigureCanvasBase.scroll_event(
<                     self, x, y, steps, guiEvent=event)
---
>     def wheelEvent(self, event):
>         x, y = self.mouseEventCoords(event.position())
>         # from QWheelEvent::delta doc
>         if event.pixelDelta().x() == 0 and event.pixelDelta().y() == 0:
>             steps = event.angleDelta().y() / 120
>         else:
>             steps = event.pixelDelta().y()
>         if steps:
>             FigureCanvasBase.scroll_event(
>                 self, x, y, steps, guiEvent=event)
488c477,480
<                 pen = QtGui.QPen(QtCore.Qt.black, 1 / self._dpi_ratio)
---
>                 pen = QtGui.QPen(
>                     QtCore.Qt.black,
>                     1 / self._dpi_ratio
>                 )
1015c1007
< class _BackendQT5(_Backend):
---
> class _BackendQT6(_Backend):

The differences being so minor, it may make sense to implement Qt6 based on Qt5 (or both vs a base).

PR Checklist

  • Has pytest style unit tests (and pytest passes).
  • Is Flake 8 compliant (run flake8 on changed files to check).
  • New features are documented, with examples if plot related.
  • Documentation is sphinx and numpydoc compliant (the docs should build without error).
  • Conforms to Matplotlib style conventions (install flake8-docstrings and run flake8 --docstring-convention=all).
  • New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
  • API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).

@jklymak
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jklymak commented Mar 9, 2021

Thanks for this, however, there is already #19255

@mfitzp
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mfitzp commented Mar 9, 2021

Thanks for this, however, there is already #19255

Oops. I'd searched + missed it. Will close

@mfitzp mfitzp closed this Mar 9, 2021
@anntzer
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anntzer commented Mar 9, 2021

@mfitzp if you could by any chance help with investigating the CI crash on #19255 that would be super helpful :)

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3 participants
@mfitzp @jklymak @anntzer