Flying Toasters — Multi-Monitor

macOS screensaver. One shared swarm of After-Dark-style flying toasters that crosses every attached display, with a full set of live-preview options. Targets macOS 26 (Tahoe) and later; tested on macOS 27.

A substantial extension of Robert Venturini's FlyingToasters that turns the saver from a single-display recreation into a true multi-monitor experience with rich, immediately-applied settings.

What's new in 2.4

Fixes for toasters and toast that stopped, vanished and restarted on macOS 27:

• No more blank screens. macOS can create a screensaver view without ever starting it (for example behind the lock screen). Those views used to draw an empty black scene at full frame rate; they now stay paused until they're started.
• One display can no longer stop the others. Stopping a view that was never started could stop the shared swarm on every display. Each view now only releases what it took.
• The full swarm appears immediately. The swarm used to fill in one sprite at a time, which took close to a minute on a four-display setup and started over after every restart. All toasters now begin part-way along their flight paths, so every display is populated from the first frame.
• Stopping no longer kills the saver process. A workaround for a macOS 14 bug called exit(0) whenever the saver stopped, which took down every display's view and made the next start come up empty. The saver now just pauses.
• Each view asks for its display's refresh rate instead of SpriteKit's default 60 fps.

Known issue: jerky motion on secondary displays (macOS 27)

On macOS 27, when a Mac's built-in display is the main display, the toasters move jerkily on every other display. The main display itself stays smooth.

Workaround: when a Mac with a built-in display is connected to external monitors, make one of the external monitors the main display (System Settings › Displays › select the monitor › Use as main display). With an external monitor as main, every display is smooth, including the built-in one.

This looks like a problem in how macOS hosts third-party screensavers on non-main displays rather than in the saver itself:

• The same drawing code runs smoothly on every display as a normal app.
• Inside the screensaver, macOS doesn't tell the saver's windows on non-main displays which screen they're on.
• Changing how the saver draws (Core Animation, classic drawing, and SpriteKit timed to each display's own refresh) made no difference.

It was seen on an M2 MacBook Air with three external monitors (one connected directly, two through DisplayLink); a Mac mini with a single monitor is unaffected. It's reported to Apple as FB24808409; this note will be updated if a macOS update fixes it.

What this fork adds

One shared world across every display

In the original, each attached display ran an independent population of toasters — sprites that exited one monitor never appeared on another. Here, a process-wide ToasterWorld singleton owns the entire toaster + cloud population. Each ScreenSaverView registers its NSScreen frame and renders its slice of the same world. Sprite positions are pure functions of CFAbsoluteTime, so per-display scenes stay in sync without any explicit coordination.

The "Number of Toasters" preference is treated as a per-monitor density and multiplied by globalDesktopArea / largestSingleScreenArea, so even L-shaped or T-shaped layouts with display gaps stay populated.

Nine live options

Every setting applies to the running preview within ~1 second of moving the slider — no need to close System Settings to see your change. All controls are sliders (or checkbox) with tick marks; no inscrutable numeric inputs.

Setting	Range	What it does
Toasters per Display	1 – 20	Density of the swarm
Flight Speed	Slow → Fast (5 ticks: Snail / Slow / Medium / Fast / Lightning)	How quickly each sprite traverses its own diagonal
Wing-Flap Speed	Slow → Fast (9 ticks, 200–40 ms/frame)	How fast the toasters flap their wings
Flight Direction	SW ↔ NW (with live label below: "down-left" / "up-left")	Which way the swarm flies
Toast / Toaster Ratio	0 – 100 %	Probabilistic mix of toast vs intact toasters
Fast Toaster Frequency	Off → 100 %	Chance any given toaster spawns as the "fast" variant
Toast Level	Light / Golden / Dark / Burnt	Browning level applied to toast sprites
Cloud Cover	Clear → Overcast (0 – 20)	Procedural cloud sprites drifting in a parallax layer behind the toasters
Constant density across displays	checkbox	Scale the toaster count so each display gets the same density; otherwise the slider value is the total population

macOS 26 (Tahoe) compatibility

macOS 26 introduced a fundamentally new screensaver hosting model — legacyScreenSaver.appex is now a sandboxed App Extension with sharp limitations on file-system writes, nib loading, and process lifetime. The Apple-shipped legacy .saver bundles (e.g. FloatingMessage) gave up entirely and now ship without configure sheets at all. This fork keeps the configure sheet alive on macOS 26 by:

• Programmatic UI. The xib is gone. The prefs window is now an NSView hierarchy built in code, which sidesteps a class of macOS 26 nib-loading bugs that left other legacy savers showing the generic "no options available" sheet.
• Sandbox-correct preferences storage. Writes go to NSApplicationSupportDirectory (sandbox-redirected to the legacyScreenSaver.appex container — ~/Library/Containers/com.apple.ScreenSaver.Engine.legacyScreenSaver/Data/Library/Application Support/Flying Toasters/prefs.plist), which is the one location the saver host is allowed to write. The ~/Library/Preferences/ByHost/ path that older savers use returns EPERM under macOS 26.
• Cross-process live preview. The Options UI and the running preview animator can spawn into separate legacyScreenSaver.appex processes, so the in-process NSNotification we use for instant apply can't reach the renderer. To get the live-preview behaviour, the animation loop polls the prefs plist once per second on a wall-clock throttle (one ~290-byte read; negligible cost).
• macOS 26 deployment target. No legacy code paths or @available branches for older OSes.

Investigation notes

While building this, every non-trivial macOS-26 quirk was documented as it came up. Useful reading if you're working on a similar project:

• docs/macos26-prefs-investigation.md — the full multi-day investigation into why .saver configure sheets fail on macOS 26, where prefs writes actually go inside the new sandboxed hosts, and what works.
• docs/multi-host-bonjour.md — design notes for a future direction: Bonjour/MultipeerConnectivity-bridged multi-Mac swarms where toasters fly across hosts on the same LAN.

Requirements

• macOS 26 (Tahoe) or later. Deployment target is 26.0.
  • On macOS 14–15 the architecture relies on legacyScreenSaver hosting every per-display ScreenSaverView instance in a single process, which is the behaviour from Sonoma onwards; the saver will install and run but most of the macOS-26-specific fixes won't apply.
• Apple Silicon or Intel Mac. Universal arm64 + x86_64 binary.

Install

Build from source. A pre-notarized binary distribution may follow in a later release; for now the source path is the supported route:

git clone https://github.com/CliveW/FlyingToasters-MultiMonitor
cd FlyingToasters-MultiMonitor
xcodebuild -project "Flying Toasters.xcodeproj" \
           -scheme "Flying Toasters" \
           -configuration Release build
cp -R "$(xcodebuild -showBuildSettings -scheme 'Flying Toasters' -configuration Release | awk -F' = ' '/ BUILT_PRODUCTS_DIR /{print $2}')/Flying Toasters.saver" \
       ~/Library/Screen\ Savers/

You'll need Xcode 17 or later, and a free Apple Developer account configured in Xcode for the local code-signing identity. Then in System Settings → Screen Saver, pick Flying Toasters and click Options to configure.

Uninstall

bash scripts/uninstall.sh

Kills the wallpaper / screensaver host processes, removes the user-level .saver bundle and prefs plist, sweeps the macOS-26 sandboxed-extension containers and wallpaper-agent caches, and prompts for sudo only if a system-level install exists. The script verifies the system is clean at the end. Safe to re-run; idempotent.

Build & run from source

Open Flying Toasters.xcodeproj in Xcode 17 or later. The Flying Toasters scheme builds the .saver bundle directly into ~/Library/Screen Savers/ via the project's INSTALL_PATH.

The Flying Toaster Test scheme is a regular .app that hosts the saver view full-screen for faster iteration — useful when you don't want to wait for System Settings to pick up bundle changes.

Architecture in one paragraph

FlyingToasterScreenSaverView is the ScreenSaverView subclass macOS instantiates per display. It hosts a SpriteKit FlyingToastersView which presents a ScreenSaverScene. The scene queries a process-wide ToasterWorld singleton for the current particle set each frame and renders the slice of those particles intersecting its display, transformed into local coordinates via screenOriginInGlobal. Particle positions are pure functions of (origin, velocity, birthTime), so multiple scenes across multiple displays stay perfectly in sync with zero inter-thread communication. Preferences live in ToasterDefaults, which posts an NSNotificationCenter event on every write so the running world re-reads its inputs immediately; a 1-second wall-clock poll inside ToasterWorld.tickAtTime: handles the cross-process case where the prefs UI and the preview animator live in different processes.

Roadmap

Possible next directions (no commitments — see the design doc for each):

• Multi-host Bonjour swarm. Discover other Macs on the same LAN via MultipeerConnectivity and exchange particle-spawn events so a toaster flying off your screen appears at your neighbour's. Design doc + honest assessment of what's actually achievable.
• Manual per-host layout UI so the multi-host transitions can be geometrically faithful, not just plausible.
• Cloud Cover assets. Procedural CG cloud sprites work but proper hand-drawn or sourced cloud art would look better.
• Toaster style variants (Winged Toast, Bach Toaster, …) — the texture-loading path is already factored for additional sets, just needs the sprite art.

Credits

• Original Flying Toasters screensaver implementation: Robert Venturini
• Toaster + toast sprite art: Originally sourced from Bryan Braun's After Dark CSS, © 1989 Berkeley Systems Inc.
• Multi-monitor extension: Clive Wright — shared ToasterWorld singleton, per-monitor density scaling, coordinate-system-robust screen matching for external displays.
• macOS 26 compatibility & preferences UI: Jordan Eunson — programmatic NSView prefs controller, sandbox-correct preferences storage in the legacyScreenSaver container, cross-process live-preview poll, the nine-option settings inventory (cloud cover, flight direction, wing-flap speed, toast/toaster ratio, fast-toaster frequency, scale-density), and the full macOS-26 investigation write-up.

License

MIT — see LICENSE.