Dark mode for Qt6

[TheForgotten69]

Summary

Fix various small issues that occured on Windows:

• Remove SetProcessDpiAwareness(1) hack that prevented Qt6 from setting its preferred DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2 context. I've tested this as I have two monitor and didn't got the transparent issue or the UI re-render on the other screen FYI. -> Already in preview now
• Replace the forced light-mode workaround with a Windows-scoped apply_theme() that respects the system dark/light
  preference. Linux/macOS keep Qt's native theming untouched.
• Add theme.py which applies the existing base stylesheet on all platforms and, on Windows only, layers QSS overrides
  (QTabWidget::pane / QTabBar contrast fixes + an adaptive progressbar) plus a white text-box fix for light mode — since
  Qt's dark mode renders tabs with no contrast on Windows.

The important gist is that the preferred mode is now respected and both light and dark are usable.

Test plan

• pre-commit run --all-files passes
• Launched the affected UI or script and exercised the change
• Tested with at least one real preset / config when relevant (note which: Change is purely UI/Visual so no need for such test here)

AI assistance

• AI-assisted — I have read every line in this diff and can defend each change

[TheForgotten69]

dark mode is scoped only on window, no custom styles either as the hardcoded white theme is handled

[dxqb]

thanks! will mark this waiting and come back to it when the Qt branch has merged

[TheForgotten69]

I saw that Qt is merged in main, any point in me rebasing @dxqb ?
Changes were minimal, scoped only to windows and can be removed down the line

[dxqb]

please coordinate this #1593

[Zueuk]

@TheForgotten69 what was the Windows problem you were fixing here? Qt Fusion style looks fine on Windows for me in both light and dark modes

[TheForgotten69]

@TheForgotten69 what was the Windows problem you were fixing here? Qt Fusion style looks fine on Windows for me in both light and dark modes

@Zueuk The issue was that light mode was activated by force and didn't respect OS preference. It was also prior to the fusion mode but tbh on a big screen I find fusion way less readable than the default windows 11 that Qt used previously (see attached)

The goal of this MR is scoped to windows only and just meant respecting OS preference, along with keeping hardcoded light style to linux. Did you got a chance to test it? I see that your PR is based on fusion so you might not have maybe?

[Zueuk]

Hmm, so just enabling Fusion probably fixed all these problems.

In my PR I basically replicated the previous OT look & feel on any platform using the Fusion style (though I was asked to disable most of it for the light theme :) There's a signal to switch themes at runtime too.

[TheForgotten69]

Hmm, so just enabling Fusion probably fixed all these problems.

In my PR I basically replicated the previous OT look & feel on any platform using the Fusion style (though I was asked to disable most of it for the light theme :) There's a signal to switch themes at runtime too.

No, Fusion is just a style. Separately, on a large screen I find Fusion noticeably less readable than the native windows11 style Qt used before (see my initial screens at the top of this MR).
If you want to replicate the style of OT, what I would suggest is:

1. I rebase my MR so it respects OS preference and use windows11 theme with minimal changes
2. Your MR base itself on this and you add any features/styling you feel necessary. So we have essentially the best of both worlds on the more modern theme rather than Fusion which is quite old atm

Does that sound good to you @Zueuk ? That way we get to use the newer and more readable theme along with all your fixes and theming :)

[Zueuk]

Fusion is a custom style that will look the same on any platform, and that's the point because Qt is a cross-platform framework. There is no need for a special treatment on Windows.

[TheForgotten69]

Fusion is a custom style that will look the same on any platform, and that's the point because Qt is a cross-platform framework. There is no need for a special treatment on Windows.

Going native isn't special-casing Windows, it's removing the special-casing. Forcing Fusion is fighting the platform default for Qt which is windows11 on windows already, which gives you the native, more readable, OS-accessibility-aware result for free.

"Same everywhere" isn't worth it if the alternative provides benefits that I already highlighted, especially given the fact it's purely styling and not ground breaking changes.

[Zueuk]

IMO it does 🤷‍♂️ quite a normal practice, I actually prefer Fusion in Qt apps.

And yeah, if platform == "Windows": ... literally is a special case, while the same code on all platforms is not.

[TheForgotten69]

IMO it does 🤷‍♂️ quite a normal practice, I actually prefer Fusion in Qt apps.

Normal practice is using the Qt provided default for each OS, which is exactly why windows11 style exists. Fusion style vs native style is taste though, you could add a style toggle next to your theme toggle, like Mod Organizer (also Qt) does in its settings.

And yeah, if platform == "Windows": ... literally is a special case, while the same code on all platforms is not.

I hadn't updated the MR yet since I wanted to discuss first, but as shown in my earlier comment the testing was scoped to Windows with the intention to be removed down the line.
To me, it sounds like we're aligned on using your work for styling. Native will always beat one size fits all on its own platform, which is why Qt ships windows11 in the first place.

[Zueuk]

Actually Qt's "native" style isn't really native - it is faked, all controls are painted by Qt anyway :) such modern GUI development 🤷‍♂️