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

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mfitzp wants to merge2 commits intomatplotlib:masterfrommfitzp:qt6-backend

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

mfitzp wants to merge2 commits intomatplotlib:masterfrommfitzp:qt6-backend

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mfitzp commentedMar 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, previouslyQt.GlobalColor.white was previously available asQt.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. SoQt.GlobalColor.white (enum) is the same in both. But alignment flags are inQt.Alignment.AlignLeft in PyQt6 andQt.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 usingexec_(), must useexec(). PySide6 is exactly the reverse.
Qt.MidButton is nowQt.MiddleButton

The code to work around these differences is inqt_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 havingexec_().

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.py158c158<                     "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 (andpytest passes).
IsFlake 8 compliant (runflake8 on changed files to check).
New features are documented, with examples if plot related.
Documentation is sphinx and numpydoc compliant (the docs shouldbuild without error).
Conforms to Matplotlib style conventions (installflake8-docstrings and runflake8 --docstring-convention=all).
New features have an entry indoc/users/next_whats_new/ (follow instructions in README.rst there).
API changes documented indoc/api/next_api_changes/ (follow instructions in README.rst there).