node-mac-virtual-display: Native Library for Virtual Display on macOS

A native library for macOS to create virtual displays for your applications using Node.js. This library uses CoreGraphics and CoreDisplay APIs to provide an interface for creating and managing virtual displays on macOS. This library is used in Tab Display, a service that allows iPads and Android tablets to be used as portable monitors.

Features

• Create and Destroy single virtual displays on macOS.
• Configurable display resolution and refresh rate.
• Create a virtual display by cloning the main display.
• Added option to select between Mirror and Extend display modes.
• Reports requested and currently active display mode information.
• Query live display state via getDisplayInfo().
• HiDPI support: physical (backing) resolution = 2x logical, with an anchor + logical mode pair so macOS recognises the display as Retina.
• Persistent main-display guard: keeps the menu bar, dock, and keyboard focus on a physical display whenever one is online (never on an invisible virtual screen), even after display topology changes such as hot-plugs.
• Support for multiple virtual displays.

See docs/IMPROVEMENTS.md for the HiDPI, main-display guard, and refresh-rate design notes and how they were verified.

Requirements

• macOS 10.14 or later
• Node.js 22 or later

Installation

Use npm to install the library:

yarn add node-mac-virtual-display

Cross-platform projects

This package declares "os": ["darwin"], so package managers know it only applies to macOS. If your project also builds on Windows or Linux, declare it as an optional dependency:

{
  "optionalDependencies": {
    "node-mac-virtual-display": "^1.0.15"
  }
}

Both parts are needed. With optionalDependencies, the os field makes package managers skip the download and the node-gyp build entirely on non-macOS platforms. Listed under regular dependencies, the os field alone does not prevent installation — the package is still fetched and the native build still runs, and fails.

Guard the require at runtime too, since the module will be absent on other platforms:

let VirtualDisplay = null
if (process.platform === 'darwin') {
  VirtualDisplay = require('node-mac-virtual-display')
}

Importing the types has the same constraint: import type still makes TypeScript resolve the .d.ts, which fails on platforms where the package was skipped. Declare the shape you need locally instead.

Usage

To create/destroy a virtual display:

const VirtualDisplay = require('node-mac-virtual-display')
const vdisplay = new VirtualDisplay()
// Clone primary display
vdisplay.cloneVirtualDisplay({
  displayName: "Clone Display",
  mirror: true
})
// OR
// To create a virtual display:
vdisplay.createVirtualDisplay({
  width: 1920,
  height: 1080,
  frameRate: 60,
  hiDPI: true,
  displayName: "Virtual Display",
  mirror: false
})

// Read back the requested mode and the mode currently reported by macOS.
// `actualRefreshRate` can be 0 when macOS does not expose a mode refresh rate.
const info = vdisplay.getDisplayInfo()
console.log(info?.requestedRefreshRate, info?.actualRefreshRate)

// To destroy a virtual display:
vdisplay.destroyVirtualDisplay()

createVirtualDisplay keeps the existing 30–120 Hz range. frameRate is given as a positive integer (e.g. 60); values outside 30–120 are clamped. The returned info object includes the virtual display ID, requested dimensions/rate, current CoreGraphics mode, and online/active state. Rates are reported exactly as supplied for create; for a clone, the actual mode rate is reported as-is (macOS can expose fractional values such as 59.94, and we do not round them). The requested rate is not a guarantee that the encoder or the remote device will deliver that many frames per second; callers should use the current mode and their transport/decoder metrics when deciding whether a stream is actually sustaining the target rate.

API reference

createVirtualDisplay(options) → DisplayInfo

Creates a new virtual display. options:

Option	Type	Default	Notes
width	number	required	Logical width in pixels (positive integer).
height	number	required	Logical height in pixels (positive integer).
frameRate	number	60	Positive integer, clamped to 30–120 Hz.
hiDPI	boolean	true	When enabled the physical (backing) resolution is 2x logical and the display is recognised as Retina.
displayName	string	"Virtual Display"	Also used as the persistent identity key (see below).
ppi	number	81	Positive, clamped to 72–300.
mirror	boolean	false	true mirrors the main display, false extends.

cloneVirtualDisplay(options) → DisplayInfo

Creates a display matching the main display's resolution and refresh rate. options: displayName (default "Virtual Display") and mirror (default false).

getDisplayInfo() → DisplayInfo | null

Returns the current display info, or null if no display is active.

destroyVirtualDisplay() → boolean

Destroys the virtual display. Returns true if a display was destroyed, false if there was nothing to destroy.

DisplayInfo

{
  id: number;                 // CoreGraphics display ID
  width: number;              // requested logical width
  height: number;             // requested logical height
  requestedRefreshRate: number;
  actualWidth: number;        // mode reported by macOS (may be 0 pre-settle)
  actualHeight: number;
  actualRefreshRate: number;  // may be 0 when macOS does not expose a rate
  isOnline: boolean;
  isActive: boolean;
}

Persistent Display Identity

This library automatically uses the Display Name (displayName) as the persistent identity key.

• Name-Based Persistence: When you create a display with displayName: "My Monitor", it receives a consistent internal ID derived from that name.
• Mac Memory: macOS will remember the window layout and resolution settings associated with that specific name.
• Simple Usage: Just use the same name next time, and your windows will be exactly where you left them.

⚠️ Note on Changing Resolutions

If you keep the same displayName but drastically change the resolution or aspect ratio (e.g., 16:9 -> 4:3), macOS might get confused because it thinks it's the same monitor. If you need a "fresh" monitor profile, simply give it a new name (e.g. "Monitor V2").

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