BlackHoleSaver — a black hole screensaver for macOS

A macOS screensaver that screenshots your desktop the moment it starts, then swallows it: your windows bend, magnify and mirror around a geodesic-traced Schwarzschild black hole with a relativistic accretion disk.

After Eric Bruneton's Real-time High-Quality Rendering of Non-Rotating Black Holes, via the single-pass adaptation from blackhole_ghostty. Each pixel's null geodesic is integrated numerically in one Metal fragment pass — everything the camera sees falls out of that integration rather than being painted on:

• the shadow — rays with impact parameter under b₍crit₎ = (3√3/2) rₛ spiral into the horizon (your windows really are gone, not faded)
• gravitational lensing — escaped rays are projected back onto the desktop "sky" plane: the screenshot bends, magnifies, and mirrors inside the Einstein ring
• photon ring — rays winding near the r = 1.5 rₛ photon sphere
• accretion disk — a thin Keplerian disk the ray may cross several times (the far side arcs over and under the shadow); blackbody color from a Shakura–Sunyaev temperature profile, shifted and beamed by the relativistic Doppler factor
• starfield — a lensed sky, shown when the desktop can't be captured

Requirements

• macOS 14 (Sonoma) or later
• Any Mac with Metal (Apple Silicon recommended)

Install

1. Download BlackHoleSaver.saver.zip from Releases and unzip it.
2. Double-click BlackHoleSaver.saver — it installs to ~/Library/Screen Savers/.
3. Select BlackHoleSaver in System Settings → Screen Saver.
4. Grant the Screen Recording permission (next section) — without it the saver shows a lensed starfield instead of your desktop.

Releases are Developer ID signed and notarized. If macOS refuses to open a copy that traveled through some other channel, clear the quarantine flag: xattr -dr com.apple.quarantine BlackHoleSaver.saver.

Build from source instead

brew install xcodegen
git clone https://github.com/s0xDk/blackhole_screensaver_macos.git
cd blackhole_screensaver_macos
xcodegen generate
xcodebuild -project BlackHoleSaver.xcodeproj -scheme BlackHoleSaver -configuration Release build
cp -R ~/Library/Developer/Xcode/DerivedData/BlackHoleSaver-*/Build/Products/Release/BlackHoleSaver.saver ~/Library/Screen\ Savers/
killall legacyScreenSaver 2>/dev/null; true

Screen Recording permission

Capturing the desktop requires the Screen Recording permission, and third-party savers run inside Apple's host process legacyScreenSaver — so the permission must be granted to that, not to the saver bundle. The "+" picker in Privacy & Security won't help: it only accepts regular .app bundles, and legacyScreenSaver.appex is an app extension inside a system framework. Drag-and-drop is the way:

1. Open System Settings → Privacy & Security → Screen & System Audio Recording.

2. In Finder, choose Go → Go to Folder… (⇧⌘G) and paste:

   /System/Library/Frameworks/ScreenSaver.framework/PlugIns/
   

3. Drag legacyScreenSaver.appex from that Finder window and drop it onto the app list in the Screen Recording settings, then make sure its toggle is on.

4. Run killall legacyScreenSaver in Terminal (or log out and back in) so the host relaunches with the permission.

Run the screensaver — your desktop falls into the hole.

Settings & presets

System Settings → Screen Saver → BlackHoleSaver → Options…:

• Preset — Inferno (default), Gargantua, M87* Donut, Face-on Ember, Quasar, Blazar, Pure Lens (no disk, pure geometry + starfield), Zen.
• Hole size — apparent shadow radius; the visible footprint spans ~1.5% of the screen at the minimum to ~12% at the max.
• Drift speed — how fast the hole wanders (0 = static centered).
• Warp reach — how far out the desktop visibly bends, in hole radii; the top of the range warps essentially the whole screen.
• Quality — render scale. Auto (default) caps the render at 1800 rows, which is indistinguishable in motion and keeps 5K/6K displays fast; Full / 75% / 50% are manual overrides.

Break timer (menu bar helper)

BlackHoleTimer.app is an optional menu bar companion: set a timer, and when it runs out the screensaver is forced on — a break reminder where the break actually happens, because your work falls into the hole.

• Presets from 5 to 60 minutes, or Custom… for any duration; while running, the menu bar icon becomes a live countdown.
• Repeat re-arms the timer after each break.
• Launch at Login keeps it around.
• Show Black Hole Now starts the screensaver immediately, no timer needed.
• If the Mac slept past the deadline, it skips firing on wake instead of ambushing you the moment the lid opens.

Install: download BlackHoleTimer.app.zip from Releases, unzip, drop it in /Applications, open. It works by launching Apple's ScreenSaverEngine, so it starts whatever saver is selected in System Settings — with its usual permissions intact.

Building from source: same steps as the saver, with -scheme BlackHoleTimer; the product is BlackHoleTimer.app.

Credits

• Eric Bruneton's black hole shader — the rendering approach.
• blackhole_ghostty — the single-pass numeric adaptation and disk model this shader is ported from.