Screensaver

A screensaver is one of the few pieces of software whose original job has gone away entirely. It existed because a CRT phosphor left showing the same image for hours would keep a ghost of it permanently, so the picture had to keep moving. LCD panels do not burn in that way, the operating system dims the display long before it matters, and the whole category quietly became decoration. This tool is the decoration, plus the one job that did survive: turning a screen you are not typing on into something worth glancing at.

Six effects. Pick one, adjust it, and press Fullscreen. Everything runs on a canvas in your browser — there is no video to download, nothing is sent anywhere, and once the page has loaded once it works with the network switched off.

Two of them are the ones people actually remember. Windows 3.1 shipped five screensavers in 1992 — Blank Screen, Flying Windows, Marquee, Mystify and Starfield Simulation — and Windows 95 kept them, renamed most of them, and added Curves and Colors. Mystify and Curves are here under their own names, and Starfield is the first effect in the list.

Starfield flies stars out of a vanishing point in the middle of the screen. Each star has a position on a plane and a depth, and the depth counts down; dividing the position by the depth is what makes a star accelerate outwards as it gets closer, which is the entire trick. At the default speed a star takes about 4.75 seconds to cross from the back of the field to the viewer — 19 seconds at the slowest setting, 1.6 at the fastest. The density control sets how many are in flight: 220 at 1×, 55 at the lowest setting and 440 at the highest. A star that passes the viewer is respawned at full depth on a brand-new track rather than wrapped back around, because recycling stars in place sends the same handful down the same handful of paths, and that becomes visible within about a minute.

Warp is a switch on the starfield rather than an effect of its own, and it draws each star as a streak back along its own track instead of as a point — the stretched-stars look familiar from Star Trek and most other starship shows. What makes it work is that the smear is measured in depth, not in pixels: the same fixed step back along the track is a couple of pixels for a star at the back of the field and most of the screen for one about to pass you, because both ends of the line go through the same division by distance. Short streaks near the middle and long ones at the edges is the whole effect. A fixed pixel length would draw uniform dashes, which reads as rain. Streak length follows the speed control, so a quarter speed is a gentle drift and 3× is the full thing; raise the density too, since 220 streaks spread thin on a large screen.

Mystify and Curves are one effect wearing two coats, which is exactly how Microsoft built them. Four points wander the screen, bouncing off the edges; every twentieth of a second the shape they define is recorded, and the last fourteen recordings stay on screen behind the live one, fading out. That trailing ribbon is the whole look, and it covers the most recent 0.7 seconds. The difference between the two is one line of drawing code: Mystify joins the four points into a closed quadrilateral, and Curves treats them as the control points of a single cubic Bézier — so two of the four are never on the line at all, which is why one reads as folded paper and the other as a ribbon. Each shape has its own colour, drifting round the full spectrum every 17 seconds, and the starting colours are spread evenly round the circle rather than picked at random: every shape drifts at the same rate, so whatever separation they start with is the separation they keep. The density control sets how many shapes there are — two by default, one at the lowest setting and four at the highest — and the vertices move between 55 and 113 pixels a second at 1×, each at its own rate, so a shape is always deforming rather than sliding.

Bouncing text is the one everyone has actually watched, waiting for the corner. Type up to 24 characters and it drifts across the screen, changing colour on every wall it touches. The horizontal and vertical speeds are deliberately different — 96 and 71 pixels a second at 1× — because equal speeds trace a diamond and come back to the same place, which is much less interesting to watch. On a 1440×900 window it takes about 12.9 seconds to cross horizontally and 11.8 vertically. A corner is counted when both walls are struck within a thirty-third of a second of each other, which at the default speed means the text landing within about three pixels of the corner. From a standing start at the top left, the first one takes just over four hours. That is roughly right: a corner hit you can get in a minute is not a corner hit.

Glyph rain drops columns of characters down the screen, brightest at the leading glyph and fading out behind it. A column is 18 pixels wide, so a 1440-pixel window holds 80 of them and a phone in portrait holds 22. The alphabet is 48 Latin letters, digits and symbols rather than the half-width katakana of the film it is imitating, and that is a deliberate limitation: this site ships no webfont, so any character your operating system lacks would render as an empty box, and any character it borrows from a different typeface would come out the wrong size next to its neighbours. Which glyph appears in a given cell is computed from the column's seed and the row number, so nothing is stored per character and a column of any length costs the same to draw. When a column finishes falling it restarts with a new seed, so the same characters never loop down the same column.

The drifting clock is the one with a use. It fills the screen with the time in your device's own timezone, with the day and date underneath, on a 24-hour or 12-hour face with seconds optional. It is meant for a phone or an old tablet propped up on a shelf where you want to be able to read the time from across the room. The clock wanders rather than sitting still: two slow sine waves on periods of 97 and 61 seconds, which are coprime, so the path does not repeat for 99 minutes. That is the one piece of genuine burn-in avoidance left in the tool — OLED phone screens really do retain a bright static rectangle left in place all evening, and a large set of glowing digits is exactly the shape that does it.

Fullscreen, and keeping the screen on. The Fullscreen button expands the stage to fill the display and hides the rest of the page; Escape or the Exit button in the corner brings it back. On iPhones, where Safari does not allow ordinary elements to go truly fullscreen, it expands to fill the browser window instead and the same Exit button works. The "Keep screen awake" switch asks the browser to hold a wake lock so your display does not dim thirty seconds into the thing you propped it up to look at. Not every browser offers that — Firefox does not, and a browser may decline — in which case the tool says so under the controls rather than pretending it worked.

Sharing a setup. The effect and every setting are packed into the part of the URL after the #, which browsers never send to a server. Copy link gives you an address that opens on exactly the screensaver you configured — useful for saving a particular clock setup as a bookmark on the device that is going to display it, which is probably not the device you set it up on.

Reduced motion. If your system asks for reduced motion, nothing starts animating on its own — the page opens paused with a Play button. That is as far as the setting can honestly be honoured here: a screensaver is motion, and an unmoving one is a picture. If flashing or fast movement is a problem for you, the clock at the slowest speed is the gentlest thing in the list, and the speed control goes down to a quarter of the default.

Every effect here is an independent implementation, written from the idea rather than ported from anything. Windows, Mystify and Curves and Colors are Microsoft's; Star Trek is Paramount's. Both are named above only to describe what these effects look like, and this page is not affiliated with, endorsed by, or connected to either company.