Initial commit: HUDini — classic volume HUD for macOS

Menu bar utility that shows a centered HUD overlay with volume bars
when system volume changes. CoreAudio monitoring, auto-fade, works
on all spaces and fullscreen.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Sources/HUDini/VolumeMonitor.swift

@@ -0,0 +1,226 @@
+import CoreAudio
+import AudioToolbox
+import Foundation
+
+class VolumeMonitor {
+    typealias VolumeCallback = (Float, Bool) -> Void
+
+    private let callback: VolumeCallback
+    private var deviceID: AudioDeviceID = kAudioObjectUnknown
+    private var isListening = false
+    private var lastVolume: Float = -1
+    private var lastMuted: Bool = false
+
+    init(callback: @escaping VolumeCallback) {
+        self.callback = callback
+    }
+
+    func start() {
+        guard !isListening else { return }
+        deviceID = getDefaultOutputDevice()
+        guard deviceID != kAudioObjectUnknown else { return }
+
+        addDeviceChangeListener()
+        addVolumeListener(for: deviceID)
+        addMuteListener(for: deviceID)
+        isListening = true
+    }
+
+    func stop() {
+        guard isListening else { return }
+        removeVolumeListener(for: deviceID)
+        removeMuteListener(for: deviceID)
+        removeDeviceChangeListener()
+        isListening = false
+    }
+
+    // MARK: - Default Output Device
+
+    private func getDefaultOutputDevice() -> AudioDeviceID {
+        var deviceID = AudioDeviceID(0)
+        var size = UInt32(MemoryLayout<AudioDeviceID>.size)
+        var address = AudioObjectPropertyAddress(
+            mSelector: kAudioHardwarePropertyDefaultOutputDevice,
+            mScope: kAudioObjectPropertyScopeGlobal,
+            mElement: kAudioObjectPropertyElementMain
+        )
+        let status = AudioObjectGetPropertyData(
+            AudioObjectID(kAudioObjectSystemObject), &address, 0, nil, &size, &deviceID
+        )
+        return status == noErr ? deviceID : kAudioObjectUnknown
+    }
+
+    // MARK: - Volume
+
+    func getVolume() -> Float {
+        guard deviceID != kAudioObjectUnknown else { return 0 }
+        var volume: Float32 = 0
+        var size = UInt32(MemoryLayout<Float32>.size)
+
+        // Try master channel first
+        var address = AudioObjectPropertyAddress(
+            mSelector: kAudioDevicePropertyVolumeScalar,
+            mScope: kAudioDevicePropertyScopeOutput,
+            mElement: kAudioObjectPropertyElementMain
+        )
+
+        var status = AudioObjectGetPropertyData(deviceID, &address, 0, nil, &size, &volume)
+        if status == noErr { return volume }
+
+        // Fallback to channel 1 (left)
+        address.mElement = 1
+        status = AudioObjectGetPropertyData(deviceID, &address, 0, nil, &size, &volume)
+        return status == noErr ? volume : 0
+    }
+
+    func isMuted() -> Bool {
+        guard deviceID != kAudioObjectUnknown else { return false }
+        var muted: UInt32 = 0
+        var size = UInt32(MemoryLayout<UInt32>.size)
+        var address = AudioObjectPropertyAddress(
+            mSelector: kAudioDevicePropertyMute,
+            mScope: kAudioDevicePropertyScopeOutput,
+            mElement: kAudioObjectPropertyElementMain
+        )
+        let status = AudioObjectGetPropertyData(deviceID, &address, 0, nil, &size, &muted)
+        return status == noErr ? muted != 0 : false
+    }
+
+    // MARK: - Listeners
+
+    private func addVolumeListener(for device: AudioDeviceID) {
+        var address = AudioObjectPropertyAddress(
+            mSelector: kAudioDevicePropertyVolumeScalar,
+            mScope: kAudioDevicePropertyScopeOutput,
+            mElement: kAudioObjectPropertyElementMain
+        )
+
+        // Try master first
+        let status = AudioObjectAddPropertyListener(device, &address, volumeChanged, Unmanaged.passUnretained(self).toOpaque())
+        if status != noErr {
+            // Fallback: listen on channel 1
+            address.mElement = 1
+            AudioObjectAddPropertyListener(device, &address, volumeChanged, Unmanaged.passUnretained(self).toOpaque())
+        }
+    }
+
+    private func removeVolumeListener(for device: AudioDeviceID) {
+        var address = AudioObjectPropertyAddress(
+            mSelector: kAudioDevicePropertyVolumeScalar,
+            mScope: kAudioDevicePropertyScopeOutput,
+            mElement: kAudioObjectPropertyElementMain
+        )
+        AudioObjectRemovePropertyListener(device, &address, volumeChanged, Unmanaged.passUnretained(self).toOpaque())
+        address.mElement = 1
+        AudioObjectRemovePropertyListener(device, &address, volumeChanged, Unmanaged.passUnretained(self).toOpaque())
+    }
+
+    private func addMuteListener(for device: AudioDeviceID) {
+        var address = AudioObjectPropertyAddress(
+            mSelector: kAudioDevicePropertyMute,
+            mScope: kAudioDevicePropertyScopeOutput,
+            mElement: kAudioObjectPropertyElementMain
+        )
+        AudioObjectAddPropertyListener(device, &address, muteChanged, Unmanaged.passUnretained(self).toOpaque())
+    }
+
+    private func removeMuteListener(for device: AudioDeviceID) {
+        var address = AudioObjectPropertyAddress(
+            mSelector: kAudioDevicePropertyMute,
+            mScope: kAudioDevicePropertyScopeOutput,
+            mElement: kAudioObjectPropertyElementMain
+        )
+        AudioObjectRemovePropertyListener(device, &address, muteChanged, Unmanaged.passUnretained(self).toOpaque())
+    }
+
+    private func addDeviceChangeListener() {
+        var address = AudioObjectPropertyAddress(
+            mSelector: kAudioHardwarePropertyDefaultOutputDevice,
+            mScope: kAudioObjectPropertyScopeGlobal,
+            mElement: kAudioObjectPropertyElementMain
+        )
+        AudioObjectAddPropertyListener(
+            AudioObjectID(kAudioObjectSystemObject), &address, deviceChanged,
+            Unmanaged.passUnretained(self).toOpaque()
+        )
+    }
+
+    private func removeDeviceChangeListener() {
+        var address = AudioObjectPropertyAddress(
+            mSelector: kAudioHardwarePropertyDefaultOutputDevice,
+            mScope: kAudioObjectPropertyScopeGlobal,
+            mElement: kAudioObjectPropertyElementMain
+        )
+        AudioObjectRemovePropertyListener(
+            AudioObjectID(kAudioObjectSystemObject), &address, deviceChanged,
+            Unmanaged.passUnretained(self).toOpaque()
+        )
+    }
+
+    // MARK: - Callbacks
+
+    fileprivate func handleVolumeChange() {
+        let vol = getVolume()
+        let muted = isMuted()
+        callback(vol, muted)
+    }
+
+    fileprivate func handleMuteChange() {
+        let vol = getVolume()
+        let muted = isMuted()
+        callback(vol, muted)
+    }
+
+    fileprivate func handleDeviceChange() {
+        // Remove old listeners
+        if deviceID != kAudioObjectUnknown {
+            removeVolumeListener(for: deviceID)
+            removeMuteListener(for: deviceID)
+        }
+        // Switch to new device
+        deviceID = getDefaultOutputDevice()
+        if deviceID != kAudioObjectUnknown {
+            addVolumeListener(for: deviceID)
+            addMuteListener(for: deviceID)
+        }
+    }
+}
+
+// C-style callbacks that bridge to the class methods
+private func volumeChanged(
+    _ objectID: AudioObjectID,
+    _ numberAddresses: UInt32,
+    _ addresses: UnsafePointer<AudioObjectPropertyAddress>,
+    _ clientData: UnsafeMutableRawPointer?
+) -> OSStatus {
+    guard let clientData = clientData else { return noErr }
+    let monitor = Unmanaged<VolumeMonitor>.fromOpaque(clientData).takeUnretainedValue()
+    monitor.handleVolumeChange()
+    return noErr
+}
+
+private func muteChanged(
+    _ objectID: AudioObjectID,
+    _ numberAddresses: UInt32,
+    _ addresses: UnsafePointer<AudioObjectPropertyAddress>,
+    _ clientData: UnsafeMutableRawPointer?
+) -> OSStatus {
+    guard let clientData = clientData else { return noErr }
+    let monitor = Unmanaged<VolumeMonitor>.fromOpaque(clientData).takeUnretainedValue()
+    monitor.handleMuteChange()
+    return noErr
+}
+
+private func deviceChanged(
+    _ objectID: AudioObjectID,
+    _ numberAddresses: UInt32,
+    _ addresses: UnsafePointer<AudioObjectPropertyAddress>,
+    _ clientData: UnsafeMutableRawPointer?
+) -> OSStatus {
+    guard let clientData = clientData else { return noErr }
+    let monitor = Unmanaged<VolumeMonitor>.fromOpaque(clientData).takeUnretainedValue()
+    DispatchQueue.main.async {
+        monitor.handleDeviceChange()
+    }
+    return noErr
+}