Expose an API to get a list of screens

Fixes #57

example.js

@@ -5,6 +5,7 @@ const aperture = require('.');
 
 async function main() {
   const recorder = aperture();
+  console.log('Screens:', await aperture.screens());
   console.log('Audio devices:', await aperture.audioDevices());
   console.log('Preparing to record for 5 seconds');
   await recorder.startRecording();

index.js

@@ -146,12 +146,22 @@ class Aperture {
 
 module.exports = () => new Aperture();
 
+module.exports.screens = async () => {
+  const stderr = await execa.stderr(BIN, ['list-screens']);
+
+  try {
+    return JSON.parse(stderr);
+  } catch (_) {
+    return stderr;
+  }
+};
+
 module.exports.audioDevices = async () => {
   const stderr = await execa.stderr(BIN, ['list-audio-devices']);
 
   try {
     return JSON.parse(stderr);
-  } catch (err) {
+  } catch (_) {
     return stderr;
   }
 };

readme.md

@@ -43,6 +43,19 @@ See [`example.js`](example.js) if you want to quickly try it out. *(The example
 
 ## API
 
+### aperture.screens() -> `Promise<Array>`
+
+Get a list of screens. The first screen is the primary screen.
+
+Example:
+
+```js
+[{
+  id: 69732482,
+  name: 'Color LCD'
+}]
+```
+
 ### aperture.audioDevices() -> `Promise<Array>`
 
 Get a list of audio devices.

swift/aperture/DeviceList.swift

@@ -1,4 +1,4 @@
-import Foundation
+import AppKit
 import AVFoundation
 import CoreMediaIO
 
@@ -15,6 +15,15 @@ private func enableDalDevices() {
 }
 
 struct DeviceList {
+  static func screen() -> [[String: Any]] {
+    return NSScreen.screens.map {
+      [
+        "name": $0.name,
+        "id": $0.id
+      ]
+    }
+  }
+
   static func audio() -> [[String: String]] {
     return AVCaptureDevice.devices(for: .audio).map {
       [

swift/aperture/main.swift

@@ -65,11 +65,17 @@ func usage() {
     """
     Usage:
       aperture <options>
+      aperture list-screens
       aperture list-audio-devices
     """
   )
 }
 
+if arguments.first == "list-screens" {
+  printErr(try toJson(DeviceList.screen()))
+  exit(0)
+}
+
 if arguments.first == "list-audio-devices" {
   // Uses stderr because of unrelated stuff being outputted on stdout
   printErr(try toJson(DeviceList.audio()))

swift/aperture/util.swift

@@ -1,4 +1,4 @@
-import Foundation
+import AppKit
 import AVFoundation
 
 private final class StandardErrorOutputStream: TextOutputStream {
@@ -24,5 +24,56 @@ extension CMTime {
 }
 
 extension CGDirectDisplayID {
-  static let main: CGDirectDisplayID = CGMainDisplayID()
+  static let main = CGMainDisplayID()
+}
+
+extension NSScreen {
+  private func infoForCGDisplay(_ displayID: CGDirectDisplayID, options: Int) -> [AnyHashable: Any]? {
+    var iterator: io_iterator_t = 0
+
+    let result = IOServiceGetMatchingServices(kIOMasterPortDefault, IOServiceMatching("IODisplayConnect"), &iterator)
+    guard result == kIOReturnSuccess else {
+      print("Could not find services for IODisplayConnect: \(result)")
+      return nil
+    }
+
+    var service = IOIteratorNext(iterator)
+    while service != 0 {
+      let info = IODisplayCreateInfoDictionary(service, IOOptionBits(options)).takeRetainedValue() as! [AnyHashable: Any]
+
+      guard
+        let vendorID = info[kDisplayVendorID] as! UInt32?,
+        let productID = info[kDisplayProductID] as! UInt32?
+      else {
+          continue
+      }
+
+      if vendorID == CGDisplayVendorNumber(displayID) && productID == CGDisplayModelNumber(displayID) {
+        return info
+      }
+
+      service = IOIteratorNext(iterator)
+    }
+
+    return nil
+  }
+
+  var id: CGDirectDisplayID {
+    return deviceDescription[NSDeviceDescriptionKey("NSScreenNumber")] as! CGDirectDisplayID
+  }
+
+  var name: String {
+    guard let info = infoForCGDisplay(id, options: kIODisplayOnlyPreferredName) else {
+      return "Unknown screen"
+    }
+
+    guard
+      let localizedNames = info[kDisplayProductName] as? [String: Any],
+      let name = localizedNames.values.first as? String
+      else {
+        return "Unnamed screen"
+    }
+
+    return name
+  }
 }