How to avoid the True-Depth frame rate dropping when the ThermalState is serious?

iPhone12 Pro, iOS 15.0.1  * Occurs on most iPhone devices

I am using True-Depth on the Front side that I got from ARKit for my own application. (ARFrame.capturedDepthData)

        ...
    func session(_ session: ARSession, didUpdate frame: ARFrame)
    {
        // get capturedDepthData
        guard let depthData = frame.capturedDepthData else { return }
        ...

There are many other processes, so the CPU gets hot as soon as I launch the app. When the CPU is hot, the True-Depth frame rate drops from about 15 to 5 fps.

Is there a way to maintain a constant frame rate?

Is there a way to get a lower resolution? QVGA resolution is enough for my app.

A simple code is attached below.

How to use:

1. Create a new project in Xcode13.0 (select"App", "Storyboard" template)
2. Replace "ViewController.swift" in the generated code
3. Prepare a suitable UI in "Main" and attach it
4. Build the app

Please use another app to heat up the CPU.

capture:

• ThermalState.nominal

• ThermalState.serious

//  ViewController.swift
import Foundation
import UIKit
import ARKit
import RealityKit

class ViewController: UIViewController
{
    // Outlet
    @IBOutlet weak var arView: ARView!
    @IBOutlet weak var depthImageView: UIImageView!
    @IBOutlet weak var fpsLabel: UILabel!
        
    private let fpsManager: FpsManager = FpsManager()

    override func viewDidLoad()
    {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        arView.session.delegate = self
        arView.session.run(ARFaceTrackingConfiguration())
    }
}
    
extension ViewController: ARSessionDelegate
{
    func session(_ session: ARSession, didUpdate frame: ARFrame)
    {
        // get capturedDepthData
        guard let depthData = frame.capturedDepthData else { return }
        let depthMap = depthData.depthDataMap
        depthImageView.image = UIImage(ciImage: CIImage.init(cvPixelBuffer: depthMap))
        
        // update log
        guard let fps = fpsManager.Update() else { return }
        let thermalStateStr = ProcessInfo.processInfo.thermalState.toString()
        let depthWidth = CVPixelBufferGetWidth(depthMap)
        let depthHeight = CVPixelBufferGetHeight(depthMap)
        fpsLabel.text = String(format: "[%d, %d], fps: %2.2f, thermalState: \(thermalStateStr)",
                               depthWidth, depthHeight, fps)
    }
}

class FpsManager {
    private var start: Date = Date()
    private var frames: Int = 0
    private let waitTime: TimeInterval = 1.0
    
    public func Update() -> Double? {
        let now = Date()
        let secFromStart = now.timeIntervalSince(start)

        if secFromStart < waitTime {
            frames += 1
            return nil
        }
        
        let fps = Double(frames) / secFromStart as Double

        start = now
        frames = 0
        return fps
    }
}

extension ProcessInfo.ThermalState {
    func toString() -> String {
        switch self {
        case .nominal:
            return "nominal"
        case .fair:
            return "fair"
        case .serious:
            return "serious"
        case .critical:
            return "critical"
        default:
            return "[error] toString(): unknown type"
        }
    }
}