Map rotation

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// Copyright 2016 Esri.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import UIKit
import ArcGIS

class MapRotationViewController: UIViewController {
    @IBOutlet private weak var mapView: AGSMapView!
    @IBOutlet private weak var slider: UISlider!
    @IBOutlet private weak var rotationLabel: UILabel!
    @IBOutlet private weak var compassButton: UIButton!

    private var map: AGSMap!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Add the source code button item to the right of navigation bar.
        (self.navigationItem.rightBarButtonItem as! SourceCodeBarButtonItem).filenames = ["MapRotationViewController"]

        // Instantiate map with topographic basemap.
        map = AGSMap(basemapStyle: .arcGISStreets)

        // Assign map to the map view.
        mapView.map = map

        // Update the slider value when the user rotates by pinching.
        mapView.viewpointChangedHandler = { [weak self] in
            DispatchQueue.main.async {
                self?.mapViewpointDidChange()
            }
        }

        // Set the map view's viewpoint.
        mapView.setViewpoint(AGSViewpoint(targetExtent: AGSEnvelope(xMin: -13044000, yMin: 3855000, xMax: -13040000, yMax: 3858000, spatialReference: .webMercator())))
    }

    func mapViewpointDidChange() {
        slider.value = Float(mapView.rotation)
        rotationLabel.text = "\(Int(slider.value))\u{00B0}"
        compassButton.transform = CGAffineTransform(rotationAngle: CGFloat(-mapView.rotation * Double.pi / 180))
    }

    // MARK: - Actions

    // Rotate the map view based on the value of the slider
    @IBAction private func sliderValueChanged(_ slider: UISlider) {
        if let viewpoint = mapView.currentViewpoint(with: AGSViewpointType.centerAndScale) {
            let rotatedViewpoint = AGSViewpoint(center: viewpoint.targetGeometry as! AGSPoint, scale: viewpoint.targetScale, rotation: Double(slider.value))
            mapView.setViewpoint(rotatedViewpoint)
        }
    }

    @IBAction private func compassAction() {
        compassButton.transform = CGAffineTransform.identity
        mapView.setViewpointRotation(0, completion: nil)
    }
}