Implement the `Device::is_dark_color_scheme` function by nicoburns · Pull Request #411 · servo/stylo

nicoburns · 2026-07-02T13:52:34Z

This is necessary (but may not be sufficient) to make light-dark() functions work.

Implementation based on the Gecko implementation: https://searchfox.org/firefox-main/source/widget/nsXPLookAndFeel.cpp#1296

The logic is:

If the user specifies a single color-scheme (light or dark) value then use that (value comes in from the ColorSchemeFlags)
Else fall back to preferred color scheme from the Device

Any ancestors of this commit are from upstream mozilla-central, with some filtering and renaming. Our patches and sync tooling start here. The sync tooling has all been squashed into this commit, based on: https://github.com/servo/stylo/commits/64731e10dc8ef87ef52aa2fb9f988c3b2530f3a7

This is a rebase of 2453c41 Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

The unit of (1 / 2px) is definitely not a px. Right now we disallow dividing by non-numbers, so enforce it. Once we implement unit math we could start tracking exponents (and support something like squared pixels etc). Differential Revision: https://phabricator.services.mozilla.com/D304694

Servo PR: servo/servo#44978 Signed-off-by: Josh Matthews <josh@joshmatthews.net>

We were previously using a mix of f32 and f64. Then it could happen that we would first check that `a < b` in f64, but when converting to f32, they might become equal due to the precision loss. Thus this could break invariants in the logic, making a `debug_unreachable!()` reachable. Servo PR: servo/servo#45682 Signed-off-by: Oriol Brufau <obrufau@igalia.com> Co-authored-by: Martin Robinson <mrobinson@abandonedwig.info>

Reverts servo#368 More work is required in Servo to integrate this.

Fixes servo#390 This feature is quite impactful as it is required for Tailwind's hover styles to work. Servo PR: servo/servo#45681 Signed-off-by: Nico Burns <nico@nicoburns.com>

…servo#388) It's not possible to properly calculate these only looking at style, because the results depends on the used `overflow` value. Servo PR: servo/servo#45629 Signed-off-by: Martin Robinson <martin@abandonedwig.info>

Fixes a compile warning from servo#388. Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Performs some changes so that Servo will be able to use these: - `ComputedFontWeightRange` - `ComputedFontStretchRange` - `ComputedFontStyleDescriptor` Servo PR: servo/servo#45821 Signed-off-by: Oriol Brufau <obrufau@igalia.com>

The implementation does the same as what gecko does (except that I didn't add support for `device-aspect-ratio`, hence slightly simpler / inlined. Servo PR: servo/servo#45490 --------- Signed-off-by: Martin Robinson <martin@abandonedwig.info> Co-authored-by: Martin Robinson <martin@abandonedwig.info>

…#400) This method was performing a single iteration. But most callers want to perform multiple iterations, so they were calling it in a loop. So this patch replaces `iterate()` with `iterate_by()`, which takes the desired number of iterations as a parameter, and returns the actual number of iterations that were performed. Servo PR: servo/servo#45978 Signed-off-by: Oriol Brufau <obrufau@igalia.com>

servo#401) It was only incremented for finite animations, but infinite animations need to be incremented too. Servo PR: servo/servo#45990 Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Needed for servo/servo#45901 The servo PR is already approved, feel free to merge this immediately. Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

I noticed a typo in the README file of the `selectors` library. Signed-off-by: Vlad Negară <150728638+VladNegara@users.noreply.github.com>

Servo PR: servo/servo#44978 Signed-off-by: Josh Matthews <josh@joshmatthews.net>

Transitions can sometimes have 0 duration when the transition reversing shortening factor is also calculated to be 0. When that happens, we should always use 1.0 for the progress when calculating the value for the transition. This avoid division by zero. Servo PR: servo/servo#46016 Signed-off-by: Martin Robinson <mrobinson@abandonedwig.info>

It's fine to subtract `n` when the value is `n`, we just don't want to get negative. Signed-off-by: Oriol Brufau <obrufau@igalia.com>

We were already passing viewport dimensions into Stylo as part of the `Device` which is sufficient to determine, `width`, `height` and `orientation`, but we were previously only exposing the `width` to CSS.| Servo PR: servo/servo#45707 --------- Signed-off-by: Nico Burns <nico@nicoburns.com>

Fixes: servo#407 Signed-off-by: Oriol Brufau <obrufau@igalia.com>

I'm implementing this in Blitz, so I would like to enable it here if possible. Should be low cost/risk for Servo as it's just `u8` bitflags. Servo PR: servo/servo#46159 Signed-off-by: Nico Burns <nico@nicoburns.com>

Signed-off-by: Nico Burns <nico@nicoburns.com>

Loirooriol · 2026-07-02T14:03:38Z

-        false
+    pub(crate) fn is_dark_color_scheme(&self, flags: ColorSchemeFlags) -> bool {
+        // The below is based on the implementation from Gecko:
+        // https://searchfox.org/firefox-main/source/widget/nsXPLookAndFeel.cpp#1296


Line number is useless if it's not a permalink.

https://searchfox.org/firefox-main/rev/0a7f146ccac85b8f413264042dcd764028d419ec/widget/nsXPLookAndFeel.cpp#1296

Loirooriol

I'm not sure I see the point of adding a function that isn't used. If you are implementing light-dark(), wouldn't it be better to add it as part of that PR?

Loirooriol · 2026-07-02T14:09:42Z

Sorry, somehow failed to see the function already exists as returning false.

Signed-off-by: Nico Burns <nico@nicoburns.com>

Loirooriol

So I guess this looks good if you use a permalink.

It's not really changing behavior because color-scheme doesn't parse, right?

nicoburns · 2026-07-02T14:17:32Z

It's not really changing behavior because color-scheme doesn't parse, right?

In theory it should make it respect the system theme (light/dark mode) which we already plug in to Stylo for @prefer-color-scheme). But I'm not sure if there are other places we need to change to make this work properly. color-scheme is just a per-element override for that.

Possibly we ought to enable color-scheme parsing, as I think most of implementation of that might actually be within Stylo?

Loirooriol · 2026-07-02T14:55:45Z

In theory it should make it respect the system theme

Then please ensure test coverage

delan and others added 28 commits June 5, 2026 19:26

Commit our changes on top of upstream Stylo

75382fd

This is a rebase of 2453c41 Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Fixup for https://phabricator.services.mozilla.com/D299242

3422488

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Fixup for https://phabricator.services.mozilla.com/D296480

1c7754c

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Fixup for https://phabricator.services.mozilla.com/D286140

7d53916

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Fixup for https://phabricator.services.mozilla.com/D301762

369ba1b

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Fixup for https://phabricator.services.mozilla.com/D296935

b061170

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Fixup for https://phabricator.services.mozilla.com/D292136

12eb772

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Add device-width/device-height media features. (servo#368)

9ed6469

Servo PR: servo/servo#44978 Signed-off-by: Josh Matthews <josh@joshmatthews.net>

Revert "Add device-width/device-height media features." (servo#394)

3a386f0

Reverts servo#368 More work is required in Servo to integrate this.

Add the pointer/hover media features (servo#391)

49e912c

Fixes servo#390 This feature is quite impactful as it is required for Tailwind's hover styles to work. Servo PR: servo/servo#45681 Signed-off-by: Nico Burns <nico@nicoburns.com>

Remove unused import: crate::computed_values (servo#398)

f59f742

Fixes a compile warning from servo#388. Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Allow Servo to use computed @font-face ranges (servo#399)

71bbb70

Performs some changes so that Servo will be able to use these: - `ComputedFontWeightRange` - `ComputedFontStretchRange` - `ComputedFontStyleDescriptor` Servo PR: servo/servo#45821 Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Make iterate() increment the iteration state for infinite animations (

49c0bc3

servo#401) It was only incremented for finite animations, but infinite animations need to be incremented too. Servo PR: servo/servo#45990 Signed-off-by: Oriol Brufau <obrufau@igalia.com>

style: Derive MallocSizeOf for ComputedFontStyle (servo#402)

64ec899

Needed for servo/servo#45901 The servo PR is already approved, feel free to merge this immediately. Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

Fix typo in selectors README (servo#379)

556f727

I noticed a typo in the README file of the `selectors` library. Signed-off-by: Vlad Negară <150728638+VladNegara@users.noreply.github.com>

Add device-width/device-height media features. (servo#397)

93f1ccf

Servo PR: servo/servo#44978 Signed-off-by: Josh Matthews <josh@joshmatthews.net>

Relax assert for paused animations to include equality (servo#404)

6b4eb30

It's fine to subtract `n` when the value is `n`, we just don't want to get negative. Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Bump stylo to 0.19.0, selectors to 0.39.0, to_shmem to 0.5.0 (servo#408)

e0bcd28

Fixes: servo#407 Signed-off-by: Oriol Brufau <obrufau@igalia.com>

Enable the touch-action property for Servo builds of Stylo (servo#409)

bc25ec9

I'm implementing this in Blitz, so I would like to enable it here if possible. Should be low cost/risk for Servo as it's just `u8` bitflags. Servo PR: servo/servo#46159 Signed-off-by: Nico Burns <nico@nicoburns.com>

Implement the Device::is_dark_color_scheme function

9110962

Signed-off-by: Nico Burns <nico@nicoburns.com>

nicoburns force-pushed the implement-device-is-dark branch from 5fea073 to 9110962 Compare July 2, 2026 13:53

Loirooriol reviewed Jul 2, 2026

View reviewed changes

Use permalink for Gecko function reference

ecbe18c

Signed-off-by: Nico Burns <nico@nicoburns.com>

Loirooriol approved these changes Jul 2, 2026

View reviewed changes

Loirooriol force-pushed the main branch from 5685b27 to a0381f1 Compare July 7, 2026 20:11

TimvdLippe mentioned this pull request Aug 5, 2026

Support color-scheme in Servo #438

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Implement the `Device::is_dark_color_scheme` function - #411

Implement the `Device::is_dark_color_scheme` function#411
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