SpinWin macOS Menu Bar App Visually Rotates Windows Using ScreenCaptureKit

Visual Window Rotation on macOS

SpinWin is a new macOS menu bar application designed to visually rotate any selected window. It achieves this effect by not directly rotating the actual window, as macOS lacks a public API for such functionality. Instead, SpinWin employs a technique that involves hiding the original window off-screen and continuously capturing its contents.

Technical Implementation

The application utilizes the Accessibility API to move the target window off-screen. ScreenCaptureKit, specifically SCStream with a desktopIndependentWindow filter, is then used to capture only the contents of that hidden window. These captured frames are subsequently drawn into a transparent, borderless overlay window positioned where the original window was. A CALayer transform is applied to this overlay, allowing for rotation at any angle, including continuous spinning. The overlay is dynamically sized to prevent clipping of the rotated content.

User Interaction and Availability

Users can activate SpinWin by left-clicking its menubar icon, selecting a rotation option (preset angles, spin speed, or free rotation), and then clicking the desired window. The overlay can be repositioned by dragging and rotated freely via a handle. Pressing Esc on the overlay stops the rotation and restores the original window. The app is available as a signed and notarized download, or it can be built from source.

Limitations

SpinWin has several limitations due to its technical approach. The overlay is not interactive, meaning clicks and keystrokes are not passed to the real window underneath. The hidden window still appears unrotated in Mission Control/Exposé. Additionally, some applications may throttle rendering when off-screen, potentially slowing the capture feed, and windows that resize themselves while rotated will maintain their original footprint.