Windowsill
A plant, a jar, a candle and a sleeping cat standing on the Windows taskbar as if it were a windowsill, in the light of the real sun and moon. It answers music at the speed of breath, asks for nothing, and tells you the time of day without a number.
Clips
Music
The sill hears whatever the computer is playing. Here it hears a plain four-on-the-floor song in the gold of a late October afternoon. Dust drifts into the light on the beat, the plant's leaves lean to the bass and nod on each kick, and the tip of the cat's tail keeps time. After twenty-two seconds the song stops, and everything settles over the next few.
A tap wakes the cat
Tap the cat and it gets up, stretches, and walks a little way before lying down again. Its legs are jointed and move only as fast as its feet cover the ground, so it never slides. Everything else it does takes seconds.
Sunset, an hour a minute
The sun goes down. The light warms, then greys, and the plant loses its colour first. The candle lights itself as the real sun sets, and the cat, which goes to lie wherever the warmth is, is already beside it.
Screenshots
About
Windowsill puts a potted plant, a glass jar, a candle and a tuxedo cat on the Windows taskbar, as if the taskbar were a windowsill. There is no drawn ledge and no window around them. Your desktop shows through everywhere else, like the glass.
They stand in the light of the real sky. The sun’s angle comes from where you are and what time it is, so the light is low and gold in the morning, short and white at midday, and warm and fading in the evening. At night it is moonlight in the moon’s real phase, and the candle.
You glance at it the way you glance at a real window. It tells you the time of day without a number.
The film above is a whole day in a minute, from before dawn to the next one. The cover is one sill across an evening: the plant at noon, the jar at sunset, the candle lit, and the cat in the night.
The Cat
The cat sleeps nearly all the time, the way a cat on a real windowsill does. A few times a day it gets up by itself and pads over to lie on whichever side of the others the sun is coming from, out of their shade. In the morning that is the east, so it walks past the plant to lie in the low sun. After dark it goes to lie by the candle while the candle burns. When the sun’s side isn’t known, it stays where it is. It never invents a reason to move.
Tap it and it wakes, stretches and settles again a little way off. Rest the pointer on it and it half opens its eyes, slow-blinks and breathes deeper, which is the nearest a picture gets to a purr.
Asking for Nothing
The design has six rules, and the code treats them as hard constraints:
- Peripheral, never central. Any change takes at least two seconds. Nothing moves faster than a leaf in a draft, and nothing snaps.
- Never asks. No notifications, sounds, badges or prompts. Every click passes through to the desktop, except on the things themselves.
- True to the world. The real sun, the real moon, its real phase. If it can’t know something, it shows plain daylight rather than inventing it.
- Steps aside. It fades out behind fullscreen apps, games and presentations, and does nothing at all while the screen is locked.
- Light on the machine. It draws at 15 fps, or 30 while music plays.
- Drawn in code. No art assets. Everything is shapes and one WGSL shader, so it stays crisp at any DPI.
The only things you can do are yours to start. Pick a thing up and carry it along the taskbar: it lifts and tips as you carry it, the flame and leaves trail back and the water sloshes, and whatever you set it down on slides aside to make room. They are where you left them the next day. Rest the pointer on the candle for a second and a tiny menu opens, where it can be told to start at login.
Light on the Machine
Measured over a minute of the running sill on a desktop with an RTX 4070:
| of one core | Task Manager | |
|---|---|---|
| Idle, 15 fps | 2.4% | 0.10% |
| Music, 30 fps | 3.0% | 0.13% |
A --bench mode draws frames offscreen, idle and with a synthesized beat, and CI runs it on Windows’ software renderer, so a shader or a loop that has grown a lot fails the build.
Next
The four inputs in the design are the clock, the music, the weather and the taskbar. Three of them are in. The fourth is next: rain beading on the glass, snow along the taskbar’s edge, and grey light, from Open-Meteo every half hour. After that the plant will remember. It will grow one leaf for each day you use the computer, flower after about a month, and wilt a little while you’re away.
How These Were Made
Everything on this page was drawn by Windowsill itself. A --film mode draws the sill offscreen at exactly 30 frames a second and writes every frame out, so the footage plays smoothly however long each frame took. It runs the real thing: the same light, the same easing, and the same cat deciding where to lie. The clock is the film’s own: Seattle on 18 October 2026, from the place’s own sun. The music is a short song synthesized for the bench. The sill is drawn at six times its size, so a 1080p frame holds the right half of it, where the things stand.
The sill itself is clear. Its frames carry their own transparency, so the dark wallpaper and plain taskbar behind it are painted in afterwards, as stand-ins for a desktop. The cover blends four of these stills, from noon to night, across one sill. The only other edits are crops and one trim.
Technical Details
- Language: Rust (edition 2024), one binary, Windows 10 and 11
- Window: winit 0.30 with Win32 extended styles (layered, click-through, no taskbar button, never takes focus), placed with
SHAppBarMessageand re-placed on display and DPI changes. While the cursor is over a thing, click-through comes off so the press lands on the sill. - Rendering: wgpu 30 into a DirectComposition surface with premultiplied alpha, one signed-distance-field WGSL shader for every object, hot-reloaded on save
- Light: the NOAA solar position formula for the sun, the Astronomical Almanac’s low-precision lunar series for the moon and its phase, and Fishbowl’s day-and-night palette, eased every frame
- Audio: WASAPI loopback capture and beat analysis from Seoul, trimmed to bass, beat, beat phase and kick. Nothing is recorded, saved or sent anywhere.
- Location: Windows’ location service, or a place set in
windowsill.toml, which is re-read on every save - Dev modes:
--day-in 60sfor a whole day in a minute,--atto hold a time,--bench, and--film