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qt: Mark canvas for re-draw after savefig #26309

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Jul 15, 2023
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qt: Mark canvas for re-draw after savefig #26309

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9 changes: 9 additions & 0 deletions lib/matplotlib/backends/backend_qtagg.py
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Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,15 @@ def paintEvent(self, event):
finally:
painter.end()

def print_figure(self, *args, **kwargs):
super().print_figure(*args, **kwargs)
# In some cases, Qt will itself trigger a paint event after closing the file
# save dialog. When that happens, we need to be sure that the internal canvas is
# re-drawn. However, if the user is using an automatically-chosen Qt backend but
# saving with a different backend (such as pgf), we do not want to trigger a
# full draw in Qt, so just set the flag for next time.
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This is going to force a full re-render the next time the window paints itself no matter which canvas class was actually selected.

The advantage of doing this rather than `self.draw_idle8 that this won't trigger the repaint and redraw on its own?

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This is going to force a full re-render the next time the window paints itself no matter which canvas class was actually selected.

Yes, this would be the same as before #25713.

The advantage of doing this rather than `self.draw_idle8 that this won't trigger the repaint and redraw on its own?

Yes, draw_idle will add a timer and actually draw later; we don't want that in order to keep the fix for #5234.

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@QuLogic Thanks for investigating this. On the side of mplcairo.qt I had the same issue, but took a slightly different approach to fix it (matplotlib/mplcairo@cd6d2ca): I stash the old renderer before calling print_figure, and then restore it at the end, which always saves the need for a redraw. Perhaps the same can be done here? (Not that I actually checked.)

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This suggests a more general change in that print_figure should always make a new canvas object even if the currently in-use canvas can technically save the format requested. This would simplify some of the logic a bit (I think) and would probably save a bunch of dpi changing work...

self._draw_pending = True


@_BackendQT.export
class _BackendQTAgg(_BackendQT):
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