More qt fractional DPI fixes - #17640

import matplotlib.pyplot as plt
import numpy as np

th = np.linspace(0, 2*np.pi, 512)

fig, ax = plt.subplots()
ax.plot(th, np.sin(th))
ax.plot(th, np.cos(th))

ax.set_title(fig.canvas._dpi_ratio)

plt.show()

Each of those was launched with

✔ 19:57:24 $ with ${...}.swap(QT_SCALE_FACTOR=2.0): 
............     python /tmp/tester.py & 
............      

There is no visual difference between this branch and master.

From what we've seen, I think that should be correct. At least, it seems like setDevicePixelRatioF and setDevicePixelRatio do the same thing... Maybe they're there in order to be extra-explicit about types.

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout v3.2.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 3460e0e7b40ab61e0626cfeebb3ae9c22f255d16

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #17640: More qt fractional DPI fixes'

4. Push to a named branch :

git push YOURFORK v3.2.x:auto-backport-of-pr-17640-on-v3.2.x

5. Create a PR against branch v3.2.x, I would have named this PR:

"Backport PR #17640 on branch v3.2.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to suggest an improvement.