A lightweight macOS utility that fixes the inconsistent corner radius rendering on fullscreen and maximized windows in macOS 26 and later.

The Problem

macOS 26 introduced inconsistent corner radius rendering for maximized windows (windows enlarged via the green button or manually resized to fill the screen). The corners appear randomly rounded with inconsistent radius, which is particularly noticeable and distracting. This does NOT affect native fullscreen apps (which work fine), only maximized windows that still show the title bar.

Before & After

The Solution

MacCornerFix monitors your active windows and automatically detects when you're using a maximized window (NOT native fullscreen). It then:

Samples the pixel colors from inside the window (near the corners)
Creates small overlay windows at each corner
Draws those sampled colors over the rounded corners to mask them

The result is corners that match your window content, eliminating the visual inconsistency.

Features

Automatic detection of maximized windows (85%+ of screen size)
Skips native fullscreen apps (they don't have the corner issue)
Smart color sampling to match window content
Lightweight menu bar app (no dock icon)
Privacy-focused (runs locally, no network access)
Low CPU usage with efficient monitoring

Requirements

macOS 13.0 (Ventura) or later
Accessibility permissions (required to detect window states)

Installation & Running

Option 1: Quick Run (Recommended for Testing)

# Navigate to the project directory
cd MacCornerFix
# Run the app directly
make run

This will build and run the app immediately without installing it to your Applications folder.

Option 2: Build and Install

# Navigate to the project directory
cd MacCornerFix
# Build the app
make build
# Install to Applications folder
make install

After installation, you can launch MacCornerFix from your Applications folder like any other app.

Accessibility Setup (REQUIRED)

MacCornerFix requires Accessibility permissions to detect window states and work properly.

First Time Setup:

Launch MacCornerFix (either via make run or from Applications folder)
You'll see a prompt asking for Accessibility permissions
Click Open System Settings (or manually open System Settings)
Navigate to Privacy & Security → Accessibility
You may need to click the lock icon 🔒 at the bottom and enter your password
Find MacCornerFix in the list and enable the checkbox next to it
- If you don't see MacCornerFix, click the + button and add it manually
Restart MacCornerFix for the permissions to take effect

If the app still doesn't work after granting permissions:

Quit MacCornerFix completely
Go back to System Settings → Privacy & Security → Accessibility
Toggle the MacCornerFix checkbox OFF and then ON again
Launch MacCornerFix again

Usage

Once running, MacCornerFix works automatically:

The app runs in your menu bar (look for the dashed square icon)
When you maximize a window (green button or manually resize), corner overlays activate automatically
Native fullscreen apps (⌃⌘F) are NOT affected - they don't have the corner issue
When you resize the window smaller, the overlays disappear
Click the menu bar icon to access About and Quit options

How It Works

Window Monitoring: Uses macOS Accessibility APIs to monitor the focused window
Fullscreen Detection: Checks both the fullscreen attribute and window dimensions
Color Sampling: Captures pixel colors from inside the window (25px from corners)
Overlay Rendering: Creates transparent overlay windows at each corner
Corner Masking: Draws the sampled colors to mask the inconsistent rounded corners

Troubleshooting

The app doesn't seem to work

Make sure you've granted Accessibility permissions
Try quitting and restarting the app
Check that the app is running (menu bar icon should be visible)

Corners don't match perfectly

The app samples colors from 25px inside the window
If your window has a gradient or complex pattern near corners, there might be slight mismatches
This is normal and usually not noticeable

Performance issues

The app updates every 0.5 seconds, which should be imperceptible
If you experience issues, please report them

Building

Requirements:

Xcode Command Line Tools
Swift 5.9 or later

# Build only
make build
# Build and run
make run
# Clean build artifacts
make clean

Privacy

MacCornerFix:

Runs entirely on your local machine
Does not collect or transmit any data
Only accesses window information necessary for functionality
Does not record or store screenshots

License

MIT License - Feel free to use, modify, and distribute.

Credits

Created to fix Apple's corner radius inconsistency in macOS Sequoia.

Contributing

Issues and pull requests are welcome! This is a simple utility, but improvements are always appreciated.

Note: This is a workaround for a macOS bug. Hopefully Apple will fix the underlying issue in a future update, making this app unnecessary.