[FIX] Canvas: Palette propagation

[ales-erjavec]

Issue

Canvas conflicts with dark theme/styles, e.g:

Description of changes

• Propagate the palette in the canvas where applicable
• Use palette's colors instead of hardcoded ones
• Add an option to specify --style=fusion:breeze-dark (the palette's colors are taken from KDE's t 'Breeze Dark' theme). This is mostly just for testing, the fusion style is not a good with dark color themes
• Suppress the default 'orange' styling in the main window if the application palette is to dark.

If deemed necessary a GUI option in the preferences dialog can also be added to select the style.

Includes

• Code changes
• Tests
• Documentation

[codecov-io]

Codecov Report

Merging #2760 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2760   +/-   ##
=======================================
  Coverage   81.67%   81.67%           
=======================================
  Files         323      323           
  Lines       55420    55420           
=======================================
  Hits        45264    45264           
  Misses      10156    10156

[kernc]

❤️

Any possibility to also support QT_STYLE_OVERRIDE env variable?

[ales-erjavec]

What do you mean? QT_STYLE_OVERRIDE works the same as always.

[kernc]

Hmm, I set QT_STYLE_OVERRIDE, which works great for other Qt5 (non-Python) apps (qBittorrent, Clementine, VirtualBox), but doesn't seem to work with Orange.

$ env | grep QT_STYLE                                                                                                                                                                                                                               
QT_STYLE_OVERRIDE=adwaita-dark

I guess it's got to do with paths and the virtualenv I have PyQt5 in.

[ales-erjavec]

Do you have PyQt5 installed from wheels?

Try using the system provided PyQt5. I.e. use --system-site-packages when creating the env or just symlink /usr/lib/python3/dist-packages/{sip.*so,PyQt5} into the created env

[kernc]

That did the trick. Looks quite good. Except the icons, perhaps, aren't best suited to dark themes.