Show extruded features

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// Copyright 2023 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
//
//   https://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 ArcGIS
import SwiftUI

struct ShowExtrudedFeaturesView: View {
    /// A scene with a topographic basemap centered on the US.
    @State private var scene: ArcGIS.Scene = makeScene()

    /// The population statistic selection of the picker.
    @State private var statisticSelection = Statistic.totalPopulation

    /// The feature layer on the scene.
    private var featureLayer: FeatureLayer {
        scene.operationalLayers.last as! FeatureLayer
    }

    var body: some View {
        VStack {
            SceneView(scene: scene)

            // Unit system picker.
            Picker("Statistic", selection: $statisticSelection) {
                ForEach(Statistic.allCases, id: \.self) { stat in
                    Text(stat.label)
                }
            }
            .pickerStyle(.segmented)
            .padding()
            .onChange(of: statisticSelection) { newValue in
                featureLayer.renderer?.sceneProperties.extrusionExpression = newValue.extrusionExpression
            }
        }
    }
}

private extension ShowExtrudedFeaturesView {
    /// Creates a scene with a feature layer.
    /// - Returns: A new `ArcGIS.Scene` object.
    private static func makeScene() -> ArcGIS.Scene {
        let scene = Scene(basemapStyle: .arcGISTopographic)

        // Set the scene view's viewpoint specified by the camera position.
        let point = Point(x: -99.659448, y: 20.513652, z: 12_940_924.0, spatialReference: .wgs84)
        let camera = Camera(lookingAt: point, distance: 0, heading: 0, pitch: 15, roll: 0)
        scene.initialViewpoint = Viewpoint(center: point, scale: .nan, camera: camera)

        // Add the extruded feature layer to the scene.
        scene.addOperationalLayer(makeFeatureLayer())
        return scene
    }

    /// Creates a feature layer from the US census feature service.
    /// - Returns: A new `FeatureLayer`
    private static func makeFeatureLayer() -> FeatureLayer {
        let featureTable = ServiceFeatureTable(url: .censusMapStates)
        let featureLayer = FeatureLayer(featureTable: featureTable)

        // Feature layer must be rendered dynamically for extrusion to work.
        featureLayer.renderingMode = .dynamic

        // Set the symbol used to display the features (US states) from the table.
        let fillSymbol = SimpleFillSymbol(
            style: .solid,
            color: .blue,
            outline: SimpleLineSymbol(color: .white.withAlphaComponent(0.5))
        )
        let renderer = SimpleRenderer(symbol: fillSymbol)

        // Set the renderer scene properties.
        renderer.sceneProperties.extrusionMode = .baseHeight
        renderer.sceneProperties.extrusionExpression = Statistic.totalPopulation.extrusionExpression

        // Set the renderer on the layer.
        featureLayer.renderer = renderer
        return featureLayer
    }
}

private extension ShowExtrudedFeaturesView {
    /// A enum for the different population statistics.
    enum Statistic: CaseIterable {
        case totalPopulation
        case populationDensity

        /// A human-readable label for the statistic.
        var label: String {
            switch self {
            case .totalPopulation:
                return "Total Population"
            case .populationDensity:
                return "Population Density"
            }
        }

        /// The extrusion expression for the statistic.
        var extrusionExpression: String {
            switch self {
            case .totalPopulation:
                return "[POP2007] / 10"
            case .populationDensity:
                // The offset makes the extrusion look better over Alaska.
                let offset = 100_000
                return "([POP07_SQMI] * 5000) + \(offset)"
            }
        }
    }
}

private extension URL {
    /// The States layer of the Census Map Service.
    static var censusMapStates: URL {
        URL(string: "https://sampleserver6.arcgisonline.com/arcgis/rest/services/Census/MapServer/3")!
    }
}

#Preview {
    ShowExtrudedFeaturesView()
}