Hi HN! I built SpinWin, a native macOS menu bar utility that visually rotates any target app window by any angle, or puts it into a continuous rotation loop.
The Origin Story:
The impetus for this came when I was scrolling on my Mac and hit a video that asked the viewer to turn their screen upside down to see an optical illusion. Since I was on a desktop display rather than a phone, I couldn't just flip my device. When I went looking for a quick utility to rotate a single window, I was surprised to find nothing out there actually did it—so I decided to build one.
The Technical Challenge & Workaround:
macOS doesn't provide a public API to rotate another application’s window. Doing it "for real" requires private SkyLight calls (CGSSetWindowTransform) and turning off System Integrity Protection (SIP)—definitely not worth it.
To make it work safely on standard macOS, SpinWin "fakes" the effect:
Moves the target window off-screen via the Accessibility API so it keeps rendering without taking up desk space.
Captures its frame feed live using ScreenCaptureKit (SCStream + desktopIndependentWindow filter).
Renders the live stream inside a transparent, borderless overlay window at the original location using a CALayer transform for smooth rotation.
Current Tech Stack:
Built natively with Swift / SwiftUI using ScreenCaptureKit and Accessibility APIs.
Limitations:
The overlay is a live, non-interactive visual proxy (clicks aren't passed through to the real window underneath), and Exposé/Mission Control will still briefly show the unrotated hidden window off-screen.
The app is open-source, signed, and notarized.
Comments URL: https://news.ycombinator.com/item?id=49049638
Points: 2
# Comments: 1