Credits

Black Hole stands on someone else's work, and that is worth saying clearly.

The gravitational lensing at the heart of this app is adapted from ghostty-blackhole by s13k — an open-source shader for the Ghostty terminal, released under the MIT License.

What comes from that project. The physics and the rendering approach: integrating null geodesics in Schwarzschild geometry with a leapfrog stepper, capturing rays that cross the event horizon, the critical impact parameter of 3√3/2 that sets the apparent shadow, the thin accretion disk with blackbody colour and Doppler beaming, and the analytic weak-field shortcut that keeps it fast. The nine visual styles are adapted from its tuner presets. That is the part that makes this look like a black hole rather than a blur filter, and it is not ours.

What was built here. The shader was ported from GLSL to Metal and rewritten to run over a live screen capture rather than a single terminal window: a ScreenCaptureKit pipeline at 30fps, the overlay window that passes clicks straight through, the roaming path, the focus timer and break cycle, the licence system, the sound, the interface, and the packaging and notarisation.

On selling it. The MIT License explicitly permits commercial use — its own text grants the right to "use, copy, modify, merge, publish, distribute, sublicense, and/or sell". Its one condition is that the copyright notice travels with the software, and it does: the full licence ships inside the app at Contents/Resources/THIRD-PARTY-NOTICES.txt. Meeting the licence is the floor, though, not the point. Credit belongs in the open.

The original project is worth your time on its own — it runs beautifully inside Ghostty, has a live tuner, and the source is far more readable than most shader code. Go and look at it.

ghostty-blackhole — Copyright (c) 2026 s13k — MIT License.
Also credited by that project: Eric Bruneton's black hole shader, for the idea and the physics it demonstrates.