Dockkit

DockKit

Framework for integrating with motorized camera stands and gimbals that physically track subjects by rotating the iPhone. DockKit handles motor control, subject detection, and framing so camera apps get 360-degree pan and 90-degree tilt tracking with no additional code. Apps can override system tracking to supply custom observations, control motors directly, or adjust framing. iOS 17+, Swift 6.3.

Contents

• Setup
• Discovering Accessories
• System Tracking
• Custom Tracking
• Framing and Region of Interest
• Motor Control
• Animations
• Tracking State and Subject Selection
• Accessory Events
• Battery Monitoring
• Common Mistakes
• Review Checklist
• References

Setup

Import DockKit:

import DockKit

DockKit requires a physical DockKit-compatible accessory and a real device. The Simulator cannot connect to dock hardware.

DockKit itself requires no special entitlements or DockKit-specific Info.plist keys. Camera apps that use device cameras still need normal camera privacy handling, including NSCameraUsageDescription. The framework communicates with paired accessories automatically through the DockKit system daemon.

The app must use AVFoundation camera APIs. DockKit hooks into the camera pipeline to analyze frames for system tracking.

Discovering Accessories

Use DockAccessoryManager.shared to observe dock connections:

import DockKit

func observeAccessories() async throws {
    for await stateChange in try DockAccessoryManager.shared.accessoryStateChanges {
        switch stateChange.state {
        case .docked:
            guard let accessory = stateChange.accessory else { continue }
            // Accessory is connected and ready
            configureAccessory(accessory)
        case .undocked:
            // iPhone removed from dock
            handleUndocked()
        @unknown default:
            break
        }
    }
}

accessoryStateChanges emits DockAccessory.StateChange values with state, accessory, and trackingButtonEnabled. Use accessory.identifier for the name, category, and UUID; hardware details are available via firmwareVersion and hardwareModel.

System Tracking

System tracking is DockKit's default mode. When enabled, the system analyzes camera frames through built-in ML inference, detects faces and bodies, and drives the motors to keep subjects in frame. Any app using AVFoundation camera APIs benefits automatically.

Enable or Disable

// Enable system tracking (default)
try await DockAccessoryManager.shared.setSystemTrackingEnabled(true)

// Disable system tracking for custom control
try await DockAccessoryManager.shared.setSystemTrackingEnabled(false)

System tracking state does not persist across app termination, reboots, or background/foreground transitions. Set it explicitly whenever the app needs a specific value.

Tap to Select Subject

Allow users to select a specific subject by tapping:

// Select the subject at a unit point in video-frame coordinates
try await accessory.selectSubject(at: CGPoint(x: 0.5, y: 0.5))

// Select specific subjects by identifier
try await accessory.selectSubjects([subjectUUID])

// Clear selection (return to automatic selection)
try await accessory.selectSubjects([])

Custom Tracking

Disable system tracking and provide your own observations when using custom ML models or the Vision framework.

Providing Observations

Construct DockAccessory.Observation values from your inference output and pass them to the accessory at 10-30 fps:

import DockKit
import AVFoundation

func processFrame(
    _ sampleBuffer: CMSampleBuffer,
    accessory: DockAccessory,
    activeDevice: AVCaptureDevice
) async throws {
    let cameraInfo = DockAccessory.CameraInformation(
        captureDevice: activeDevice.deviceType,
        cameraPosition: activeDevice.position,
        orientation: .corrected,
        cameraIntrinsics: frameIntrinsics(from: sampleBuffer),
        referenceDimensions: frameDimensions(from: sampleBuffer)
    )

    let detection = try await detector.detect(sampleBuffer)
    let observationType: DockAccessory.Observation.ObservationType = switch detection.kind {
    case .face: .humanFace
    case .body: .humanBody
    case .object: .object
    }

    let observation = DockAccessory.Observation(
        identifier: detection.id,
        type: observationType,
        rect: detection.rect,       // normalized, lower-left origin
        faceYawAngle: detection.faceYawAngle
    )

    try await accessory.track([observation], cameraInformation: cameraInfo)
}

Observation Types

When reviewing custom tracking, explicitly choose among the only supported ObservationType cases: .humanFace, .humanBody, and .object. Do not answer with only .humanFace when body or object detections are possible.

The rect uses normalized coordinates with a lower-left origin (same coordinate system as Vision framework -- no conversion needed).

Camera Information

DockAccessory.CameraInformation describes the active camera; do not hardcode placeholder device, intrinsics, or frame-size values. Set orientation to .corrected when coordinates are already relative to the bottom-left corner. In review answers, reject opaque optional cameraInfo placeholders and show construction from the active AVCaptureDevice plus the current CMSampleBuffer.

Track variants also accept [AVMetadataObject] instead of observations. Use the image: CVPixelBuffer overloads when DockKit should combine observations or metadata with the captured image buffer; the image argument is required in those overloads.

Framing and Region of Interest

Framing Modes

Control how the system frames tracked subjects:

try await accessory.setFramingMode(.automatic) // documented default
try await accessory.setFramingMode(.center)    // explicit opt-in

Default system behavior often centers the primary subject, but .center is never the default-like mode; .automatic is. Use .left or .right when graphic overlays occupy part of the frame.

Region of Interest

Constrain tracking to a specific area of the video frame:

// Normalized coordinates, origin at upper-left
let squareRegion = CGRect(x: 0.25, y: 0.0, width: 0.5, height: 1.0)
try await accessory.setRegionOfInterest(squareRegion)

Use region of interest when cropping to a non-standard aspect ratio (e.g., square video for conferencing) so subjects stay within the visible area.

Motor Control

Disable system tracking before controlling motors directly.

Angular Velocity

Set continuous rotation speed in radians per second:

import Spatial

// Pan right at 0.2 rad/s, tilt down at 0.1 rad/s
let velocity = Vector3D(x: 0.1, y: 0.2, z: 0.0)
try await accessory.setAngularVelocity(velocity)

// Stop all motion
try await accessory.setAngularVelocity(Vector3D())

Axes:

• x -- pitch (tilt). Positive tilts down on iOS.
• y -- yaw (pan). Positive pans right.
• z -- roll (if supported by hardware).

Set Orientation

Move to a specific position over a duration:

let target = Vector3D(x: 0.0, y: 0.5, z: 0.0)  // Yaw 0.5 rad
let progress = try accessory.setOrientation(
    target,
    duration: .seconds(2),
    relative: false
)

Also accepts Rotation3D for quaternion-based orientation. Set