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Fix Cairo backends on HiDPI screens #21025

Merged

anntzer merged 3 commits into matplotlib:master from QuLogic:cairo-hidpi

Sep 14, 2021

Member

QuLogic commented Sep 9, 2021 •

edited

PR Summary

Since Cairo renderers exist forever, we need to ensure they are using the correct DPI, or else physical sizes are incorrect.

Fixes #21024.

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).

The text was updated successfully, but these errors were encountered:

QuLogic added the backend/cairo label

QuLogic added this to the v3.5.0 milestone

QuLogic force-pushed the cairo-hidpi branch from 7a356c2 to 790daec

Contributor

jklymak commented Sep 9, 2021

So Cairo doesn't support mixed dpi screen setups?

anntzer reviewed

lib/matplotlib/tests/test_figure.py Outdated

  
                    fig.savefig(buf, format='png')

                    ratio2 = Image.open(buf)

                assert ratio1.size == ratio2.size

Contributor

anntzer Sep 9, 2021

I guess even the whole images should be the same?

Member Author

QuLogic Sep 9, 2021

True, but they're empty figures, so I didn't bother. I thought of using check_figures_equal, but I don't know how to force a different backend with it.

Contributor

anntzer Sep 12, 2021

You could actually plot something, and do a plain rgba array equality check?

Member Author

QuLogic Sep 13, 2021

Sure

anntzer approved these changes

Contributor

anntzer left a comment

I don't have a mixed dpi setup to test, but at least for single-screen simulated highdpi, this does what it says on the tin.

Member Author

QuLogic commented Sep 9, 2021

So Cairo doesn't support mixed dpi screen setups?

If you mean multiple screens, that's handled at the canvas level. If you mean something like PDF, I'm not sure, but I think the Agg/PDF backends are just as broken.

Contributor

jklymak commented Sep 9, 2021

Yeah I meant screen one is non-retina and screen two is retina, and you drag the window from one to the other.

Member Author

QuLogic commented Sep 9, 2021

Yes, that depends on the backend supporting it, but e.g., QtCairo does support that.

QuLogic force-pushed the cairo-hidpi branch from 790daec to db759fd

dstansby approved these changes

Member

dstansby left a comment

Checked locally and confirmed that the fix works

QuLogic added 3 commits


          Use correct DPI when drawing in Cairo renderers

0c021c7

Unlike the Agg renderer, the Cairo renderer exists forever and is at the
DPI when the figure was created. This needs to be updated before drawing
or things in physical sizes (e.g., text or line widths) will be the
wrong size.


          Set device pixel ratio when saving a figure

630f25f

Otherwise, `FigureCanvasBase.get_width_height` returns a size scaled
down by the current pixel ratio, even though the DPI is not scaled up.
This causes the saved figure to be cropped.


          De-duplicate some unit conversion in Cairo

QuLogic force-pushed the cairo-hidpi branch from db759fd to 9598205

anntzer merged commit 9bbef1e into matplotlib:master

28 checks passed

meeseeksmachine added a commit to meeseeksmachine/matplotlib that referenced this issue


          Backport PR matplotlib#21025: Fix Cairo backends on HiDPI screens

38cf9e7

meeseeksmachine mentioned this pull request

Backport PR #21025 on branch v3.5.x (Fix Cairo backends on HiDPI screens) #21070

Merged

QuLogic deleted the cairo-hidpi branch

QuLogic added a commit that referenced this issue


          Merge pull request #21070 from meeseeksmachine/auto-backport-of-pr-21…

97db802

…025-on-v3.5.x

Backport PR #21025 on branch v3.5.x (Fix Cairo backends on HiDPI screens)

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