I love adaptive interfaces and technology that blends in more than the average human. I’ve spent literally years tinkering with ‘frecency’ ordered lists, bought a meural screen and have recently been glorying in the fantastic GNOME Adaptive Brightness.

On that last point, whilst GNOME already has Automatic Screen Brightness, and it is a good feature, dmy3k’s extension goes further on the specific machines with cool hardware: steadier behaviour with changing light, smoother transitions and brightness curves you can tune. One of the things I’ve been exploring with extensions recently is ’this feature, only more so’ and adaptive brightness is a good example.

Living far from the equator, evenings happen. The room goes grey, the window stops being a useful light source and GNOME is still cheerfully in light mode because I told it to be bright at the time one takes screenshots. Night Light is already doing its bit by then. The display has warmed up, which is nice, but the rest of the interface lacks the level of ‘darque’ required. I wanted the normal GNOME appearance preference to follow the day as well: light while it still feels like day, dark once the evening has properly arrived. Users of other operating systems may be aware of this feature, but for the purposes of this blog post let us pretend that everything below is entirely unique.

So I hacked up Sunset Appearance, a small GNOME Shell extension for GNOME Shell 45 to 50. At civil dusk it writes the same setting GNOME Settings uses:

org.gnome.desktop.interface color-scheme = 'prefer-dark'

At civil dawn it sets it back to:

org.gnome.desktop.interface color-scheme = 'default'

My dad was an aviator, so I got to hear a lot of exciting words growing up, such as ‘civil twilight’, which always makes me think of Romeo and Juliet. Sunset turns out to be a surprisingly slippery concept, and very longitudinally mediated. In London in summer there can be plenty of useful light after the sun has dipped below the horizon, and the desktop does not need to go ‘darque’ the moment the sun touches the skyline. Nautical and astronomical twilight are too late for an interface preference, and in some places at some times of year they can fail to happen in the normal way at all.

Civil twilight is when the centre of the sun is 6 degrees below the horizon and when it really does feel like the world has changed character.

Location is awkward too, because civil dawn and dusk need latitude, longitude and date. There’s some interesting fallback logic to infrequently get a coarse location (good enough for a city) and then fall back to cached data if available as Night Light already needs much the same information. Frequent readers will remember my concerns over London, Ontario being above London, England in many search boxes so there is no virtue in making the user type London into another small box. If neither source has usable coordinates, nothing changes.

Manual override behaviour is another thing that avoids annoyance. If the extension sets dark mode at dusk and I then change GNOME back to light mode, I meant that. After any override, it waits until the next scheduled dawn or dusk transition before touching the setting again.

Solar time code has an unreasonable number of edges for something everyone thinks they intuitively understand. Keeping with my aggressive policy on internationalisation the tests keep London as the ordinary case, then poke at time zones, date line longitudes, DST changes, Antarctic stations, Arctic towns, awkward offsets such as Lord Howe and Chatham and cases where civil dawn or dusk may not exist at all. My time reading brr and pretending to be in New Zealand to solve work bugs was not poorly spent.

Right now Sunset Appearance can be built from source. At some point I may choose to distribute it more widely, or even see if someone has already solved my problem better.