HiDPI Scaler

A lightweight macOS menu bar app that enables HiDPI (Retina) scaling on external displays that don't natively support it.

Many external monitors — especially ultrawides and budget 4K panels — don't offer HiDPI modes in macOS. HiDPI Scaler fixes this by creating a virtual display with 2x backing resolution and mirroring your physical display onto it, unlocking crisp Retina-quality text and UI.

Features

• Menu bar app — no dock icon, stays out of your way
• Auto-detects connected displays with native resolution, aspect ratio, and scale info
• Generates resolution presets matched to your display's aspect ratio
• One-click enable/disable
• Supports all aspect ratios: 16:9, 21:9, 32:9, 16:10, 3:2, and more
• Launch at Login via macOS Login Items
• Auto-connect on Launch — automatically re-activates your last configuration
• Settings persistence — display selection and resolution saved across sessions
• Clean teardown on quit — no orphaned virtual displays

Requirements

• macOS 13.0 (Ventura) or later
• Apple Silicon or Intel Mac

Installation

Grab the latest .dmg from Releases, open it, and drag HiDPI Scaler into your Applications folder. No build step required.

Build from source (optional)

Requires Swift 5.9+ toolchain.

git clone https://github.com/txdadlab/HiDPIScaler.git
cd HiDPIScaler
chmod +x build.sh
./build.sh
cp -r "HiDPI Scaler.app" /Applications/

Usage

1. Click the sparkles icon in the menu bar
2. Select your target display from the dropdown
3. Pick a resolution preset or enter a custom resolution
4. Click Enable HiDPI
5. macOS will apply HiDPI scaling to your display

To disable, click the menu bar icon and press Disable HiDPI.

How it works

HiDPI Scaler uses private CoreGraphics APIs (CGVirtualDisplay) to:

1. Create a virtual display with 2x pixel backing (e.g. 3840x2160 backing for a 1920x1080 logical resolution)
2. Mirror your physical display onto the virtual display using CGConfigureDisplayMirrorOfDisplay
3. macOS sees the virtual display's HiDPI modes and applies Retina scaling to the physical panel

This is the same technique used by tools like BetterDisplay, implemented as a focused, single-purpose utility.

Project structure

HiDPIScaler/
├── Package.swift                          # SPM package definition
├── build.sh                               # Build + bundle script
├── HiDPIScaler.png                        # Source icon (1024x1024)
├── Resources/
│   ├── AppIcon.icns                      # App icon bundle
│   └── Info.plist                         # App bundle metadata
└── Sources/
    ├── CGVirtualDisplayBridge/            # Obj-C bridge to private CG APIs
    │   ├── CGVirtualDisplayBridge.m
    │   └── include/
    │       ├── CGVirtualDisplay.h
    │       └── module.modulemap
    └── HiDPIScaler/                       # Swift app
        ├── HiDPIScalerApp.swift           # Entry point (MenuBarExtra)
        ├── Display/
        │   ├── DisplayManager.swift       # Display enumeration
        │   └── MirroringManager.swift     # Mirror configuration
        ├── State/
        │   └── HiDPIState.swift           # App state + presets
        ├── Utilities/
        │   └── Logger.swift
        ├── Views/
        │   └── MenuBarView.swift          # SwiftUI menu bar UI
        └── VirtualDisplay/
            └── VirtualDisplayController.swift

Known limitations

• Uses private Apple APIs — may break with future macOS updates
• Requires ad-hoc code signing (not notarized)
• Some displays may not respond to mirroring configuration

License

MIT